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AKARI FIS Data User Manual

1. Glitch Type 1 Glitch Type 2 Glitch Type 3 4 Glitch Type Glitch Tail For glitch detection using Median Transformation method Serjeant 22 23 24 25 26 27 mtgl_typel mtgl_type2 mtgl_type3 mtgl_type4 mtgl_tail no_peri_corr Glitch Type 1 Glitch Type 2 Glitch Type 3 Glitch Type 4 Glitch Bad No periodic noise correction available 64 AKARI FIS Data Users Manual 33 For SUSSEXtractor 28 sx_peak threshold detection 29 sx_source source detected 1 30 sx_obj anomalous detected 31 32 reserved 6 Quality bit quality 40 NDET Quality Flag for each pixel condition 33 gb_conv_to_volt 1 2 qual_cv_param conversion quality from ADU to Volts 35 gb_ramp_curve_corr 3 4 qual_rc_param accuracy of correction parameters 5 6 qual_rc_cf correction factor difference between corrected and the original data 3 gb_differentiation 7 8 qual_df_eq order of polynomials number of points used gb_dc_responsivity_corr make_DC_cal_lamp_table 9 10 qual_rp_data accuracy of the derived cal lamp intensity from data in a cal lamp on 11 12 qual_rp_param availability of cal lamp on to derive a correction factor 13 14 qual_rp_table quality of the correction table fluctuation etc 35 correction for flat fielding 15 16 qual_ff_param quality of the parameters for flat fielding 17 18 qual_ff_c
2. Jl J LPF 0 90cm LPF 0 220cm gt Y y LPF 0 70cm HPF 0 133cm N160 WIDE L WIDE S N60 180 140 m 180 110jm 110 604m 80 50um stressed Ge Ga array Ge Ga array for FTS mode dichroic BS is replaced by output polarizer Figure 2 1 2 The filter configuration of the FIS photometric bands LPF is the Low Pass Filter Occasionally the lamps are continuously turned on to provide a stable irradiation In addi tion the Cal B system is a lamp located in the middle of the FIS optical path Its light passes through the beam splitter reaching both detector arrays This Cal B system will be used as a backup for the Cal A system Both of these two sets of lamps are used solely for monitoring the relative responsivity variation of the detectors The absolute flux calibration will be made with celestial objects In addition to the calibration lamp sets there is a black body source on the inner wall It is used for calibration of the FTS Shutter There is a shutter at the entrance aperture of the FIS The instrumental dark level can be measured by closing the shutter During the All Sky Survey the shutter is closed periodically to monitor the dark level Leakage at the 1 200 at every passage of the polar regions level has been observed in the pre flight measurement No significant leakage has been observed although a detailed qua
3. Plot A FISv plot window as the one shown in Figure A 3 3 will appear FISy Plot Window FIS20060802053000_1800_lw fits gz 4 Spool 41 Crid tea ro a al el gt Print es star irr sftag FET Close _ L d Figure A 3 3 Detector 10 signal plotted against AKARI satellite time 96 AKARI FIS Data Users Manual Table A Dump of the data into a text format file is also possible with the action button Table see Figure A 3 4 FIS Data Table Figure A 3 4 Dump of data into text format file Print Print out the currently displayed graph image Button Print will give the option to print out the currently featured graph or to save it as a postscript file Print Ral a is Figure A 3 5 Printer setup dialog PS A postscript file can also be generated from the PS button A window with the configuration options will appear Version 1 3 September 14 2007 97 Configure PostScript Device Page size Le X Size 20 00 Y Sizer 45 00 Xx Offset 4 85 Y Offset 3 00 Orientation Landscape BLA Font Type Vector Hershey Fonte Units Centimeters Bold Jikel Akit Tierras Encapsulation OFF ort dBi italic Jedi J lis Directions Poesies Hodet Nore ot poe Font h r 12 ToTu o Helatint OFF a o A HIDE aon ite Color Output On page with left or right buttons Click the middle button in the wi
4. 0 50 100 150 200 250 300 Wavenumber cm Figure 3 1 7 The reflectivity and transmittance of the dichroic beam splitter The blue and green curves are the reflectivity in the SW channel side The two curves deviate around 160 and 180 cm 3 1 6 Stray Light It is found that the light from the Earth can enter the cryostat under certain configurations of the current orbit Ideally such light should be reflected back outside the telescope into space however a small amount of scattered light may in fact enter the telescope and be detected in the IRC and FIS instruments The stray light is most strongly observed over about 100 days with a maximum at the Summer solstice when the telescope is observing the northern sky The effect was most significant during observations of the NEP region in Phase 1 Most of the Mission programmes and Open Time proposals were carried out after September when the stray light should be much smaller The intensity of the stray light seems to be 20 100 of the dark sky Also it is larger at the beginning and end of a pointed observation Two methods are suggested to remove stray light effects in the standard Slow Scan data reduction tool Section 4 2 5 For point source observations median filtering methods can remove all large scale radiation components 26 AKARI FIS Data Users Manual WIDE S ch30 Sky brightness after dark subtraction 1 MJy sr lt gt 10 16 W incident power to FIS apertu
5. The default coordinate system is Equatorial J2000 LON_CENTER lon_center LAT_CENTER lon_center Centre position of the image By default centre position is estimated from the input data These options are useful when one wants to compare the images from different data sets of nearby sky Units are in degree in the corrdinate system specified LON_SIZE lon_size LAT_SIZE lat_size GRID_SW Image size in degrees By default image size is automatically determined to cover the input data Useful to make consistent set of images from different observational data sets grid_sw GRID_LW grid_lw Grid size of the resulting image map in arcsec Default values are AOT FISO1 FISO2 SW 15 arcsec 30 arcsec LW 30 arcsec 60 arcsec Smaller grid sizes for low redundancy data may result in many void pixels in the image Note that the grid size has the lower limit given by the program automatically and too small values for the parameters are truncated to the lower limits The values are defined as grid_limit beam_size 3600D n_int scan_speed 15 s where beam_size is 40 and 60 arcsec for SW and LW detectors BAD_THRSHLD bad_thrshld Responsivity of each pixel derived from the observational data is compared with the nominal value in the responsivity table and if the difference is larger than a factor specified by this option the data of that pixel is not used throughout the o
6. ss_make_map procedure makes use of the following routines ss_resp_corr returns the absolute responsivity ss_q_to_radec calculates equatorial coordinates for each pixel from the quaternion in the GADS or AOCU data ss_trans_corr improves transient effects after calibration lamp operation ss_eg_Ipf applies median boxcar smooth low pass filtering to extract DC slow components Earth shine ss_eg_slrmv extracts slow component and stray light from time series data by an easy way with median boxcar smooth filter ss_coad_image Constructs co add images of the entire array ss_make_map produces the following output files FIS_ SW LW _ _ar sav Time series processed data RA amp DEC position and parameters tt ar denotes After Reduction FIS_ SW LW _ _img sav Co add image data RA amp DEC position and parameters FIS_ SW LW _ _img_ w n fits image map of wide narrow band FIS_ SW LW _ _err_ wln fits error map statistical uncertainty of each pixel of wide narrow band image FIS_ SW LW _ _num_ w n fits density map number of data points contributed to each pixel of wide narrow band data FIS_ SW LW _ _img jpg co add image as jpeg image with CUBE_FITS option the following files are created instead of _img _err _num files FIS_ SW LW _ _cube_ w n fits Description about the image files are given in the previous section FIS_ SW LW _ _ar sav are the IDL save file that contains the following info
7. 0 a 2 2 4 Saturation Limits for FISO1 FISO2 2 2 5 FISO3 FTS Spectroscopy 000 ee ee ee 2 2 6 Performance of FISO3 e a 3 Instrumental characteristics 3 1 Imagine Quality omiso pow ek a Da A ee ee 3 1 1 Point Spread Function PSF a bo pew ee eae ed DIAS 3 1 2 Cross talk and ghosts raa ac ar sauce p aa naa a a i i a SS Leakage sit a A ra a Cet lit gee ae T a a Ss Bok a T A a Tina gide DRONO a aa ao ests anh Save 8 SP Moe a Ro Gee A S 3 1 5 Polarization 42 fee eds BAO Oa A ee OG Stray LISA st ane Roe eee ee GP te Re a a Ee Ra 3 2 Detector and instrument responsivity 2 2 e 3 2 1 _DEAd pixels iaee sos aee ek Be EGS ae a ewe es 3 2 2 Responsivity and Uniformity 04 32 37 Excess NOISE ix 4 04 ar a de do Pe ele e hae ag S gi 204 JRamp Curves tire Say genous B bh A ON eee T 3 2 5 Saturation After Effect 2 2 2 0 2 00002 2 eee 3 2 6 Transient response 0 2 02 eee ee es 3 2 7 Spectral Responsivity a 3 3 Charged Particle Hits Glitches aaa e A aes 3 4 Diffuse and Point Source Confusion o oa a e 0000002 ee ee 3 4 1 Confusion Due to Diffuse Background Emission 3 4 2 Confusion Due to Point sources 2 2 ee ee 320 ETS mode hara ale Soe Ga lee ke HE Patek ee a ee ee eas Version 1 3 September 14 2007 iii 3 5 1 Transient Effects on the FTS data o 35 3 5 2 Detector
8. CTOF R So far for the limited number of regions tested this calibration is consistent with COBE DIRBE even in very dark sky areas Bobs MJy sr 4 2 3 Point source photometry based on preliminary initial results Images generated by the standard Slow Scan data reduction tool are in brightness scale units of MJy sr Aperture photometry on these images should give the flux of the sources in Jy Results of aperture photometry often depend on the size of the aperture and the sky area This effect is significant in the FIS observations especially in the LW channels In the following we give an example photometry analysis using the calibration standard stars Preliminary conclusions are e There are systematic differences between the measured flux and the expected flux from the model e The ratio of two fluxes seems to be constant within 20 lo for the examined sources brighter than about 2 Jy The procedures are explained below Photometry following this method should in essence provide consistent results Note that this is not the definitive solution that will eventually be provided 46 AKARI FIS Data Users Manual All data were taken in FISO1 with 8 arcsec sec scan speed and 70 arcsec shift length Data taken with other scan speeds or with F1S02 need further consideration Section 5 3 1 Images are generated using a local flat field with a sigma clipping threshold of 1 5 and a grid size of 7 5 arcsec for SW and 15
9. NO_DISPLAY nodisp Input targetdir directory that contains _ar sav files produced by ss_run_ss you want to combine Output Image files in IDL save file and FITS format in the directory Options Most of the options for ss_mosaic_image are the same as ss_run_ss and already explained in the previous section An only unique option for this module is AOT_MIX Note that no lower limit is applied for GRID_SW and GRID_LW parameters AOT_MIX Use all available data in the directory See Explanation below Explanation ss_mosaic_image searches for all processed scan data _ar sav file in the target directory and constructs images using all available data It assumes that the directory contains a uniform data set i e same AOT and AOT parameters If data files of different data Version 1 3 September 14 2007 101 sampling modes are in the target directory the program takes the mode of the first found file normal OS list order AOT_MIX option forces the program to use all available data regardless of their sampling modes The internal algorithm and the results are the same as those of the standard ss_run_ss tool Note that this program attempts to make an image that covers all available data If the directory contains scan data that is spatially far from the others the program tries to allocate a huge amount of memory for the creation of the image plane which could cause many problems
10. absolute Flux Calibration are not yet implemented in the pipeline structure The input and output of each procedure are TSD object references on memory within 40 AKARI FIS Data Users Manual IDL Physical TSD files are not created by default until the end of the pipeline Parameters are provided in an appropriate calibration constants file CCF see Section 6 2 Four of these GB modules flag bad data flag anomaly after reset conversion to voltage units and ramp curve correction are also part of the Slow Scan pointed observation data reduction tools and are described in the next section 4 1 2 Green Box Modules used in the Slow Scan data reduction process These GB modules are automatically called from the Slow Scan toolkit At present there are little or no options available therefore users do not need to pay special attention to them They are described here only for information and clarity Setting the flags to bad data GB_Flag_Bad_Data This function sets flags in the data with the following conditions Frame condition blank frame in SAA near moon Each pixel condition dead pixel saturated pixel reset position These flags are applied to each frame sampling and each pixel The output is stored in the branch FIS OBS under Flags of the TSD file see Section 6 1 Besides this specific module for flagging data all the Green Box modules of the All Sky Survey pipeline set frame pixel flags in the case where the p
11. see Section 4 2 5 5 3 Photometric calibration 5 3 1 Scan speed Most observations of the flux calibration targets are carried out in FISO1 with a scan speed of 8 arcsec sec Tf your observation uses a higher scan speed 15 arcsec sec or 30 arcsec sec the observed signal would be reduced due to detector transient effects and will result in an underestimation of the source flux An investigation into these effects has recently begun The initial report implies that the measured flux from the aperture photometry for the 15 and 30 arcsec sec data are 10 20 fainter than that from the 8 arcsec sec case Reliable calibration information for all scan speeds will be given as soon as this analysis has been concluded 5 3 2 Calibrators Correction factors are derived for all detectors from the different calibrators see Section 4 2 8 The photometry uncertainty is estimated to be 20 SW and 30 LW However for the ol 52 AKARI FIS Data Users Manual N160 band special care is needed as only three objects were available for calibration measure ments 5 4 Attitude Determination During the Pointed Observations The attitude information for the FIS pointed observations is provided from two sources The on board computer AOCU Attitude and Orbit Control Unit calculates the satellite attitude and these results are downlinked to the ground as telemetry data together with the data from the on board sensors The Ground based Attitude Determina
12. 0 5 or 1 0 sec see text Resolution Full resolution SED Target position 0 1 2 see text Instrument operation The instruments are set up for the FTS mode The filter wheel is rotated to switch from the empty hole to the polarizer Detector readout mode is switched to high frequency sampling mode Only data from the WIDE detector arrays are acquired During the observation the moving mirror is driven Two path lengths i e spectral resolutions are available See Sec tion 2 1 4 The spectral resolution is 0 36 cm for the Full resolution mode and 2 4 cm for the SED mode The SED mode provides better quality spectra than the Full resolution mode spectra after being smoothed to a corresponding resolution There are four choices for the reset interval similar to the other FIS AOT s However CDS readout mode is not available Scan operation The FTS spectroscopic observation is operated in a staring pointing mode To minimize the dead time No Step Scan Micro Scan nor Slow Scan is carried out during a pointed observation User specified parameters The following inputs are given by the observer Target position is a new parameter added after launch Resolution mode Full resolution or SED See the description above Reset interval Four choices from 0 1 0 25 0 5 and 1 0 sec are available As the CDS mode for the brightest targets cannot be used for the FIS03 AOT a shorter reset interval of 0 1 sec is alterna
13. AKARI project is 2000 January 1st 00 00 00 UTC Version 1 3 September 14 2007 55 6 1 5 Status The Status Flags and Quality of TSD columns are composed of multiple elements of the TBIT type i e the TFORM definitions of FITS standard are 8X 16X etc Figure 6 1 2 shows an example of the status section of this document The left hand number shows the element index The fv displays this index when we click the expand button The first element index 1 corresponds to the MSB bit31 in the binary The next is the element name which cannot be defined in the FITS standard However we define the element name and write them to each header of the HDU For example the element names of status in FIS_LOBS extension are written in the header of its HDU as follows TELEM6 CREON SHTOP FWPOSON FWPOS_B1 FWPOS_BO MPOSON MPOS_B1 MPOS_BO The user should use the element name to access the status bits rather than element index 2 Status Status are provided in the telemetry packet Each status is copied from the corresponding bit in FIS_OBS packet All four band s status are included considering possible interference bit_status 32 FIS instrument status MSB bit3 1 1 CRE on 1 off 0 0x09 1 2k Shutter open 1 close 0 0x09 1 3 FW Position sensor on 1 off 0 Ox09 1 Al Filter Wheel Position bit 1 Ox09 1 5k Filter Wheel Position bit 0 Ox09 1 6 M
14. FIS on board software with an accuracy as good as the readouts They can alternatively be operated by commands if necessary The status of the shutter and calibration lamps are all recorded for the data processing The survey observation sequence and the AOTs Astronomical Observation Templates are designed by combining these elemental operation units Version 1 3 September 14 2007 13 2 2 The FIS Pointed Observations AOTs 2 2 1 FISO1 Slow Scan Observations for Photometry Mapping of Small Area The FISO1 AOT is designed for photometry of point sources and or mapping of small areas up to 25 x 10 arcmin Table 2 2 3 FISO1 summary Fixed parameters Observing Mode Photometry Band N60 WIDE S WIDE L N160 Scan pattern Two round trip scans with a cross scan shift User specified parameters Sampling mode Nominal or CDS Reset interval 0 5 or 1 or 2 sec for Nominal sampling mode Slow Scan speed 8 or 15 arcsec sec Shift length 70 or 240 arcsec Co add mode Instrument Operation The instrument is operated in the photometry imaging mode all four FIS photometric bands N60 WIDE S WIDE L N160 retrieve data The detector operation parameters are fixed at the recommended values provided by the instrument team Two readout modes are possible Nominal and CDS Scan Operation An observation consists of two sets of round trip scans in the in scan direction with a shift in the cross scan direction The ro
15. Figure 4 1 1 1 flagging of the bad data 2 correc tion of non linearity arising from cryogenic readout electronics CRE 3 differentiation of the signal ramps 4 detection of cosmic ray glitches 5 correction of transient and cross talk effects 6 subtraction of dark current level 7 correction of DC responsivity and 8 flux calibration Local Data Server INPUT Time Series Data TSD 1 Object Reference Used for Slow Scan data reduction Flagging bad data GB_Flag_Bad_Data GB_Flag_RstAnon Conversion from ADU to Volt GB_Conv_to_Volt CRE Ramp Curve Correction GB_Ramp_Curve_Corr 2d CCF Status lt lt CCF t CCF Differentiation GB_Differentiation 2dt CCF Glitch detection GB_Set_Glitch_Status_GP GB_Set_Glitch Status MMT CCF Making DC Cal lamp table GB_Make_DC_Cal_Lamp_Table tt CCF Transient Cross Talk correction GB_Transient_Corr CCF Responsivity Table Making Dark Table GB_Make_Dark_Table lt _ _ CCF Dark Table Dark Subtraction GB_Dark_Subtraction DC Responsivity Correction GB_DC_ResponsivityCorr Absolute flux calibration GB_Flux_Calib QUE OUTPUT Calibrated TSD Figure 4 1 1 Outline of the flow of the time series data through the Green Box pipeline modules TSD refers to Time Series Data and CCF for Calibration Constants Files The input and output of each procedure are TSD object reference Blue boxes Transient Cross talk correction
16. Response Inhomogeneity o e e 35 3 5 3 Spectrum Reproductivity o 36 30 4 ETIMSeS carro E a A AA A es 37 3 5 5 Interference from the Cryocooler o e 37 3 007 IDELect r postom 2a aa a A Ge Bo ld A 37 4 Data processing 38 4 1 AKARI All Sky Survey ASS Pipeline o o e 39 4 1 1 Out line of the data flow 0 0 0 02 e 39 4 1 2 Green Box Modules used in the Slow Scan data reduction process 40 4 2 Slow Scan processing and calibration FISO1 and FISO2 41 4 2 1 Detecting glitches of cosmic ray hits 0 o 41 4 2 2 Calculation of signal current 2 2 e Al 4 2 3 Dark signal subtraction and flat fielding 0 Al 4 2 4 Conversion to surface brightness o e e e 42 4 2 5 Background offset subtraction e 00 eee ee ee 43 4 2 6 Making images by co adding multi pixel data 44 4 2 7 Image processing for multiple pointings 45 4 2 8 Photometric calibration o e 45 4 3 FTS spectroscopy processing FISO3 48 AL OVERVIEW o a ls he oe ee E A Oa RR eae i 48 4 3 2 Brief description of each process 1 0 0 00 0 o 49 4 3 3 Further limitations in the functionality of the current version of the FTS COOKI ee A Lie ae eee tees nee Gee ed a 50 5 Caveats in the Data Processing 51 5 1 Treatment for tra
17. a bright point source See text for details A FISO1 observation of a bright point source is shown in Figure 3 1 3 the colour scale is adjusted to emphasise the faint features Points to note are e The target on the SW images does not look like a point source but shows long exten sions along the detector array dimensions It is more significant in the direction of 20 pixels cross scan These extensions are considered to be due to cross talk between the pixels Both optical cross talk and electrical cross talk possibly contribute to this The phenomenon has not yet been completely understood therefore at present users should administer special care when they discuss the detailed morphology of targets e We also see spider like features around the target that are probably due to the telescope optics Version 1 3 September 14 2007 23 e We observe ghost images in all detectors The ghost image on the N60 detector appears when the target object is passing through the WIDE S detector The same relation holds for ghosts on WIDE S as well as the WIDE L N160 pair though it is not clearly recog nized in the WIDE L band in Figure 3 1 3 The cause of these ghost images is not yet clear The strength of the ghost image is less than 1 probably 0 3 of the target in the same image for the SW and around 10 in the LW detectors Users should take special care when looking at images of bright targets Figure 3 1 4 and 3 1 5 show time p
18. add mode is referred to as the nominal mode and is generally used for both the All Sky Survey and the Slow Scan modes FISO1 FISO2 of the FIS CDS Correlated Double Sampling mode is designed to avoid saturation in very bright regions such as the inner galactic plane The detectors are reset at every two samplings and on board differentiation of these two samplings is retrieved as the signal Therefore the downlinked data is already differentiated This mode is occasionally used in the All Sky Survey and Slow Scan mode FISO1 FIS02 Bias Light for the LW detectors The Ge Ga detectors generally have a strong transient response i e the detector does not respond instantaneously to the incoming flux but rather has a delay of a few hundreds seconds time scale see Section 3 2 6 In the All Sky Survey a point source passes across a detector pixel in 1 4 1 7 seconds This is too short for the detectors to reach a steady level corresponding to the source flux Accordingly the point source sensitivity decreases This effect is particularly serious for the LW detectors stressed Ge Ga detectors and in the low flux condition dark sky weak sources In order to reduce the impact of this effect we decided to add a bias light This takes the form of a set of thin stainless wires put in front of the LW aperture During the survey a constant current will be used to give a steady photon flux into the detector array The point source sensi
19. and a Bias Light Section 2 1 3 is used for the LW array In both these cases the time constants are 10 30 sec Since AKARI FIS almost always observes the sky in scanning mode an understanding of the effect of the transient response to the observed data is essential The most extreme case is 30 AKARI FIS Data Users Manual data fis20050107_123258 dat_001 075_lw_0 999999999VC6 txt 09 1 0 0 8 Ch12 corrected 0 7 0 6 05 Y os 1 002 x 1 0 0 2779 x exel X 0 046 0 1722 x expl X 0 423 0 4 i 2 4 5 3 Time min Figure 3 2 14 An example of Saturation after effect for a LW detector pixel The differential signal for a constant irradiation is plotted against time after the saturation In this figure an attempt is made to fit the data by a two component exponential function More detailed analysis is ongoing the All Sky Survey in which a point source is scanned in only 0 2 0 4 sec much smaller than the transient time constant resulting in a lower output signal than expected by a factor of a few Figure 3 2 16 This also affects the detection limits The effect is less severe for the Slow Scan mode for the pointed observations Ideally the transient response should be understood and reproduced by modeling the charge transfer in the detector element However strong non linear physics prevent us from making a perfect model The analysis is continuing For the All Sky Survey data the point source flux is p
20. and end at ENDDEFINE Data body starts with DATA and end at ENDDATA The data definition appears before the data body The definition part contains a line starting with one of C constant A array or S structure followed by variable type and array dimension Structure definition also includes description of the structure in a similar style Detailed explanation with examples are given below Data body part contains actual value s corresponding to the data type and dimension in the definition part In case of array or structure they are read in the order of the definition Header The header contains information about the CCF file which is used to maintain it Syntax HEADER NAME CCF name SET_NO CCF set number REV_NO Revision of the data STATUS Validated or test version RANGE Applicable data range in AFTIME CREATOR Creator of the CCF CDATE Create date of the CCF FMTVER CCF Format version COMMENT Comments ENDHEADER 74 AKARI FIS Data Users Manual Example HEADER NAME C2VT_ SET_NO 001 REV_NO 001 STATUS TEST RANGE 0 00000 0 00000 CREATOR MAKIUTI CDATE 2005 07 12T14 16 58 FMTVER 001 COMMENT Threshold for conversion to Volt from ADU ENDHEADER A constant parameter The data definition contains only one line starting with C that is followed by data type Syntax DEFINE C type ENDDEFINE DATA value HENDDATA Example DEFINE C double ENDDEFIN
21. are calculated for a v v constant spectrum at the central wavelength defined in Table 2 1 1 The same information is shown for the LW detectors in Figure 3 2 11 e In flight a Pre flight La A ut 10 ane sett ate 3 ae a e e e SW Responsivity V s MJy sr f wa t ai 3 0 20 40 60 80 100 Pixel number Figure 3 2 10 In flight and pre flight responsivities of all pixels in the SW detector arrays See figure 3 2 9 for the definition of the pixel number 28 AKARI FIS Data Users Manual e In flight a Pre flight LW Responsivity V s MJy sr Pixel number Figure 3 2 11 In flight and pre flight responsivities of all pixels in the LW detector arrays See figure 3 2 9 for the definition of the pixel number 3 2 3 Excess Noise After the results of the early FM performance tests the FIS introduced two noise filters the first in the cryogenic part near the detector and the other outside the cryostat These filters successfully reduced the noise significantly The typical frequency of the excess noise is close to the data sampling rate Therefore the noise component especially affects the All Sky Survey observations which uses every data sampling A software module to reduce this noise component has been implemented into the survey data reduction pipeline and is working successfully On the other hand the Slow Scan data reduction toolkit calculates the slope of every integration ramp to deri
22. are included in the distri bution package in order to avoid compatibility problems It is highly recommended to keep and use the distributed IDL Astronomy libraries and please be sure that your IDL set up will not cause version conflict with the package The standard set up as instructed in this cookbook should not cause such a problem A 1 2 Distribution package The fisdr software package is obtained from the Observation Support web page as a tar gzipped file The file is named as fisdr_YYYYMMDD tar gz where YYYYMMDD indicates the version The package is composed of several directories containing All the Slow Scan tool programs and calibration parameter files e GreenBox modules from the All Sky Survey Pipeline including the Calibration Constant Files CCF see Chapter 4 e The IDL Astronomy Library e The FIS Data Visualizer FISv see Section A 3 The distribution package also includes the startup directory which contains the initialization files of the FIS data reduction environment They start up IDL and set up the appropriate environment variables MDL is a product of IIT Corporation http www ittvis com id1 77 78 AKARI FIS Data Users Manual A 1 3 Setting and Starting up fisdr under Unix environment The setup procedure described here is for Unix including Linux MacOS File extraction Extracting the FIS reduction package file will create a directory reduction _YYYYMMDD and will put all files in it It is
23. for the first scan in the SED mode The average spectrum is then taken Spectral correction factor and flux calibration The spectral correction factors are primarily made from the spectra of the internal calibration source These include the correction for the wavenumber dependent response and the relative sensitivity of the pixels At present celestial calibration sources have not been taken into account thus the difference between the spectra of the internal sources and external sources is not taken into account and thus absolute flux calibration is not applied Removal of fringes In the present toolkit only fringes in the SW full resolution mode are reduced using model calculations of an airy pattern with a period of 2 53 cm Since the spectral correction factors are made using data from the internal calibration source which are in the SED mode fringes in SED mode observations should be removed when the spectral correction factors have been applied For Full Resolution mode observations the fringes are removed from both the observed data and the spectral correction factor using an airly pattern of the corresponding wavenumber resolution Residual fringes and LW fringes are not reduced in the present version of the toolkit 50 AKARI FIS Data Users Manual 4 3 3 Further limitations in the functionality of the current version of the FTS toolkit e Transient correction e Wavenumber calibration Apodization Wavenumber depende
24. ii Normalized responsivity o a 0 0 1 11 21 31 41 51 1 11 21 Channel Channel 31 41 Figure 3 5 20 The relative responsivity variation of the detector pixels in the FTS mode inte grated over effective wave numbers of 85 160 cm for the SW array left and 65 85 cm for the LW array right These data are obtained from the internal calibration source 3 5 3 Spectrum Reproductivity In order to evaluate the stability of the spectroscopic data three spectra were taken during the laboratory tests The first two were taken with a one hour interval then the third one was obtained after three hours The derived three spectra are almost equivalent to each other within about 10 0 04 0 03 0 02 Normalized output 0 01 0 00 E ey 50 60 70 80 90 100 Wavenumber cm Figure 3 5 21 The internal calibration source spectra of LW pixel 7 obtained over the first year of the AKARI mission They are normalized by the integration over the effective wavenumber of 65 85 cm In orbit the reproductivity of spectra from the internal calibration lamp was examined Figure 3 5 21 shows the spectra over the first year of the mission The spectra are consistent with each other within 10 after scaling with the integration over the effective wavenumber For most LW pixels it has been confirmed that the spectra can be reproduced to within 10 Although the spectra of the SW channel show large amplitude fring
25. of the calibration lamps are indicated Filters and Photometric bands Figure 2 1 2 describes the filter configuration of the FIS photometric bands The LW narrow band filter was replaced in 2004 with a new filter with a cut off at 70 cm 143 um This extended the band profile shortward and results in a better effective responsivity Following this change we now denote the longest FIS band as N160 instead of the previous name N170 Calibration Lamps Two sets of calibration lamps are installed in the FIS The Cal A system consists of two lamps placed in front of the SW and LW detector arrays They can be operated individually so that the optimal calibration procedure for each detector array can be realized An important role of the Cal A lamp is to produce a pulse flash to simulate the passage of a real point source The pulse flashes were planned periodically e g every minute to monitor and correct the time variation of the detector responsivity However analysis of the PV phase observations showed strong after effects due to slow transient response see Section 3 2 6 thus the periodically pulse flashes every minute are now omitted for the pointed observations ln the current calibration sequence the duration of pulse is 0 47 sec for the LW array and 0 24 sec for the SW array Version 1 3 September 14 2007 T Incident photons Blocking Filter o 430cm amp 300cm y Dichroic Beam Splitter o 91cm
26. the detector responsivity time variation caused by the calibration lamp by iterpolating the signal level at before and well after the lamp Default is OFF MEDIAN_FILTER Apply a median filter to the time series data for removing remaining background offsets between the pixels as well as excess by stray light from the Earth shine This median filtering is only applicable for point sources Diffuse sources with a spatial scale comparable to the WIDTH _FILTER used see below would be also filtered out by this process The default filter width is 40 seconds SMOOTH_FILTER Similar to MEDIAN_FILTER but use boxcar smoothing to evaluate the background offsets instead of the median The default filter width is 40 seconds WIDTH_FILTER previously known as WIDTH_MEDIAN The width of the MEDIAN_FILTER SMOOTH_FILTER in units of seconds The default is 40 seconds SIGMA sigma Sigma clipping threshold for the map making Default is 2 0 Smaller values e g 1 5 may improve the output quality with a risk of less data points used to make the maps T_START t_start T_END t_end 86 AKARI FIS Data Users Manual Specify start and end of the data used to make the images Given in units of seconds counted from the beginning of the TSD data The defaults are T_START T_END PV data 750 sec 1350 sec Phase 1 amp 2 630 sec 1350 sec GALACTIC ECLIPTIC Specify the coordinate system of the output images
27. the resent results of careful analysis of the FIS in orbit performance the sensitivity of the FIS has been further updated from the previous IDUM In summary the SW bands N60 WIDE S detection limits are worse than the pre launch predicteions i e as documented in the Observer s manual by factor of 2 3 For the LW bands N160 WIDE L various factors have brought the sensitivity to a level a factor of four 0 5 sec integration to eight 2 sec integration worse with respect to the pre launch values published in the Observers Manual It should be mentioned that these numbers are not the results of source extraction and number counting Further technical charanges are needed to draw the maximum performance of the FIS instrument Table 2 2 5 The 50 detection limits for the FIS AOTs FISO1 amp FISO2 See Tables 2 2 3 2 2 4 for relevant scan speeds for the two AOTs Numbers are per scan see text for details Point Source mJy Scan speed __Sarcsecjsec 15 aresec se 3D aroseo se Reset 05s 10s 20s CDS 05s 10s 20s CDS 055 105 208 0D5 N 260 180 130 400 280 200 420 420 84 60 42 92 92 130 95 67 200 140 100 270 230 670 470 330 1000 710 500 1400 1100 21000 Diffuse Source MJy sr Scan speed 8 arcseo se 15 arcsec sec 30arcsec se R 05s 10s 20s 005 055 105 205 CDS 05s 10s 20s CDS N60 5 6 4 5 2 8 97 8 4 5 6 4 3 120 11 8 4 28 3 0 12 2 0 57 9 7 The performance of t
28. which the detector is sensitive varies from one pixel to another probably because of inhomogeneous stress among the pixels Figure 3 2 18 demonstrates the pixel by pixel variation of the spectral responsivity of the LW channel It is seen that the cut off wavelength ranges from 165 185 wm The N160 band extends longer than the WIDE L band as the detectors are under even higher pressure The plots in Figure 3 2 17 are regarded as the typical profiles Revision of the overall RSRF with the in flight data has not yet been completed CH46 GH47 CH49 GH50 CH51 CHS2 CHS3 CHS4 CH55 GHS6 CHS9 CH60 Normalized at Peak o a 40 50 60 10 80 90 100 40 50 60 10 80 90 100 Wavenumber cnr Wavenumber cm Figure 3 2 18 Pixel by pixel variation of the spectral response of the LW detector The difference in wavelength profile directly influences the photometric accuracy especially for cool targets such as molecular clouds The error in photometry is less than a few per cent for sources warmer than 100 K but is more than 10 for a target of 30 K Version 1 3 September 14 2007 33 3 3 Charged Particle Hits Glitches The preliminary in orbit measured average glitch rate on the FIS detectors is 1 pixel min for both the SW and LW arrays There are also observed after effects of the glitches The LW detectors show the strongest effects with after effects of time scales of 1 sec At present su
29. 100 200 MB Ihttp fits gsfc nasa gov 53 54 AKARI FIS Data Users Manual TSD Tine Status Telemetry Detector Data Flags Branch boolean analog analog boolean Quality Counter Editable frame flags FIS_OBS pixel flags Figure 6 1 1 An overview of Time Series Data TSD structure 6 1 3 Nomenclature of Data Type Data type are expressed in C like notation in the following descriptions bit 1 bit O or 1 byte 1 byte unsigned byte gt 0 short 2 bytes integer long 4 bytes integer longlong 8 bytes integer float 4 bytes single precision floating point double 8 bytes double precision floating point We express the elements of status column n where n is the element index defined in the FITS 6 1 4 Time stamp e The main purpose of time stamp in the data reduction system is to synchronize the infor mation taken with different instruments and other information sources e g for pointing reconstruction e For this purpose time information maintained in TSD is that already corrected various delays It is the time when the data is sampled by the instruments e Time in the on board clock is 36 bits with LSB of 1 512 sec Practically 32 bits data either with 1 32 sec or 1 512 sec are stored in the packet depending on the instruments Internally we use a 64 bits integer long64 in IDL for time field e The original point of the time for the
30. 60 WIDE S WIDE L N160 Slow Scan speed 15 or 30 arcsec sec Scan pattern One round trip scan Sampling mode Nominal or CDS Reset interval 0 5 or 1 0 or 2 0 sec Slow Scan speed 15 or 30 arcsec sec Co add mode Instrument operation The operation of the instrument with this AOT is the same as FISO1 except that FIS02 carries out a single round trip only and that the choice of scan speed is 15 or 30 arcsec sec Scan operation The difference of this AOT from FISO1 is that an observation consists of only a single round trip scan The scan speed is chosen from 15 or 30 arcsec sec The scan length is approximately 1 and 2 deg depending on the scan speed User specified parameters The following inputs are given by the observer Detector readout mode Nominal CDS Same as FISO1 Reset interval Same as FISO1 Target position The satellite is operated such that the target position is located at the center of the scanned area 16 AKARI FIS Data Users Manual Pre cal sequence 630 Scan_p15 Post cal sequence Settling time AR Shut_opn 420 3 Shut_cls 1351 Scan area length f r 19 On target On target 802 5 1177 5 0 77 deg for 8 s A area center or source Each scan 345s v Shut_cls MA Y 1005 Shut_opn Turn 30s wits 997 6 Cal_off sequence 990 Scan_m15 Cal_on Figure 2 2 9 The scan sequence of the AOT FIS02 Version 1 3 September 14 2007 17 2 2 3 Performance o
31. 81641_1770_cube_ w n fits Compare the jpeg files with those attached in the package If they look identical the toolkit works as it is supposed to Note that the results may be different if the version of the toolkit is different A file called VERSION included in the data distribution package contains the version of the toolkit used to generate the jpeg files Looking at Images Several image data files are created by ss_run_ss pro _img jpg jpeg format image files _img sav image data in IDL save set files _img_ w n fits image map of wide narrow band data _err_ w n fits error map of wide narrow band data _num_ w n fits density map of wide narrow band data _cube_ w n fits image error density maps are in a cube fits file The _img sav files contain the following data IDL gt restore AKARI_FIS_1234567_001 FIS_SW_20061225081641_1770_img sav IDL gt help COAD_DET DOUBLE Array 2 144 170 Image of WIDE coad_det 0 and NARROW coad_det 1 detectors in MJy sr COAD_STDERR DOUBLE Array 2 144 170 Error map of the WIDE NARROW detectors RMS of the data points per pixel COAD_NUM DOUBLE Array 2 144 170 Density map of the WIDE NARROW detectors IM_LAT_COORD DOUBLE Array 144 170 IM_LON_COORD DOUBLE Array 144 170 Position of all pixels of the image array in degrees DATA_TYPE STRING FIS_SW type of input data Either FIS_SW or FIS_LW V
32. 8x101 150 10 Semele rumba Figure 4 2 2 Glitch example Glitch events are detected by taking the 1st and 2nd differential of the data and comparing the differential signal with the RMS noise Then a glitch event is flagged for each pixel There are more complex glitch detection algorithms prepared for the All Sky Survey data However for Slow Scan data this algorithm is sufficient and faster 4 2 2 Calculation of signal current The slope of an integration ramp or signal in V s is proportional to the photo current which in turn is a measure of the number of photons falling on the detector per unit time The signal current is calculated by a linear fit to the ramps In the case that glitches are detected in a single ramp the ramp is divided into number of glitches 1 and a linear fit is made for each segment of the divided ramp The weighted average flux of each segment is calculated as the mean flux for the ramp concerned The uncertainty or fluctuation of the slope is the RMS of the fit residuals The RMS noise of the LW detectors is very similar between shutter close dark signal and shutter open sky signal For the SW detectors the shutter open noise is slightly higher than that with shutter close see Fig 4 2 3 The noise spectrum is under investigation Preliminary results shows no clear difference in the noise spectra between shutter open close signals as shown in Fig 4 2 4 4 2 3 Dark signal subtraction and flat fielding
33. 9 6 151 3 162 9 174 6 186 2 Chapter 3 Instrumental characteristics In this chapter the different effects due to the properties of the detector instrumental effects caused by the electronics and optics and other external influences to be corrected during the processing of the FIS observations are described 3 1 Imaging Quality 3 1 1 Point Spread Function PSF It was impossible for the AKARI team to carry out a ground based end to end performance test for the telescope and instruments in the cryogenic environment After the launch the telescope focus was adjusted using the IRC data During the PV phase and the calibration time in Phase 1 amp 2 various measurements of the PSF were carried out As expected the actual image from the FIS observations is influenced by many complicated instrumental characteristics Investigation of the most reliable PSF information is still ongoing Only preliminary data is shown at the moment Figure 3 1 1 and Figure 3 1 2 compare the measured PSF with a Gaussian and theoreti cal PSF model Airy function of the telescope FIS instrument optics The central part 2 arcmin for SW 3 arcmin for LW of the observed PSFs can be well fitted by a Gaussian function of FWHM 37 1 39 1 5843 amp 614 arcsec for N60 WIDE S WIDE L and N160 respectively The measured PSFs are based on the observations of asteroids Theoretically the PSF of broad band imaging observations depends on the colour of the ta
34. AKARI FIS Data User Manual Version 1 3 Eva Verdugo Issei Yamamura and Chris Pearson with contributions from Mai Shirahata Shuji Matsuura Yoko Okada Sin itirou Makiuti Noriko Murakami and Mitsunobu Kawada IEuropean Space Astronomy Centre ESAC ESA Institute of Space and Astronautical Science ISAS JAXA 3Nagoya University Japan September 14 2007 Version 1 3 September 14 2007 Revision Record Date Revision Comments Mar 2007 Release of version 1 0 Mar 2007 Updated toolkit setup instructions in Appendix A Jun 2007 Updated processing options explanation Sep 2007 FTS sections updated FIS 01 02 sensitivity numbers updated i Additional information about ghost added CA ppendix A updated according to the new pipeline version Contents 1 Introduction 1 1 Purpose of this document e 1 2 Relevant information 2 Instrument and AOT Overview 2 1 Hardware Specification e Zi Overview wie at o a A tt a Eba 2 1 2 Optics and Filters e e 21 3 Detector System ii e Peo A a es 2 1 4 The Fourier Transform Spectrometer FTS 2 1 5 Instrument Operation 0 200 eee ee ee ee 2 2 The FIS Pointed Observations AOTs 2 o 2 2 1 FISO1 Slow Scan Observations for Photometry Mapping of Small Area 2 2 2 FIS02 Slow Scan Observations for Mapping of Large reas 2 2 3 Performance of FISO1 amp FISO2
35. DR_ROOT for sh etc FISDR_USER_SETUP Some users have their own IDL setup for example the display colour mode etc They are often given in idlrc An IDL batch script file specified in this environ ment variable is executed during the startup process and will set appropriate parameters Note that the fisdr standard setup may over ride the user s setup setenv FISDR_USER_SETUP idlrc for csh tsch etc and FISDR_USER_SETUP idlrc export FISDR_USER_SETUP for sh etc Details of the startup procedure When the fisdr command is executed it checks the FISDR_ROOT environment variable If the environment variable is not set it assumes the default location ASTRO F reduction Then it sets the IDL_STARTUP environment variable to the standard fisdr setup script FISDR_ROOT startup pro startupfisdr startup_fisdr is a simple IDL batch file that calls fisdr pro which actually sets the fisdr internal environment variables The startup script fisdr over rides the IDL_STARTUP variable originally set by the user If users want to apply their own IDL setting the FISDR_USER_SETUP should be used to specify a setup script The file is actually executed in fisdr pro Note that the calling the script given by FISDR_USER_SETUP is before the main setup in fisdr pro and the users setup may be overrode Also it is not guaranteed that the fisdr system will work properly with the user s setup IDL 6 2 and later versions run the startup script ever
36. E DATA 2 55837499234 this is an example of a constant ENDDATA An array parameter The data definition part starts with an A to indicate that the data is an array Data type and array dimensions follow Up to 8 dimensions IDL limit can be specified Note that the left most index changes first IDL standard in the multi dimensional arrays an array of dim1 dim2 is created in the example below The array values are given in the data body part Any blank space tabs or new lines are recognized as a delimiter i e the values can be split over multiple lines Version 1 3 September 14 2007 75 Syntax define A double dimi dim2 enddefine data valuei value2 value3 value dimixdim2x enddata Example define A double 2 3 enddefine data 12 3 commenti 5 5 3E 10 comment2 6 5 enddata A structure parameter The definition part of the structure CCF begins with a S and the dimension size of the structure Components of the structure Tag are specified in the following lines A tag definition starts with a T and a structure tag name then data definition constant or array see below The data body is included for each tag Therefore there are the same number of pairs of FDATA and ENDDATA as the number of tags in the definition In order to identify each data body with the data tag the data body starts with a I and the tag_name before the values A data
37. ID but is different for parallel mode observations TARGETID 1234567 Target ID SUBID 1 Sub ID Unique number to specify the observation OBJECT target Object name Object name SURVEY for survey mode observations OBJ RA 320 5533 degree Target position OBJ DEC 23 3325 degree Target position Target position recorded in observation database Only for pointed observations Values are in double precision AOT FISO 1 Observation AOT AOT Used for the information FISO1 FISO2 IRCO4 IRCi1 SURVEY Version 1 3 September 14 2007 59 AOTPARAM 8 0 5 70 AOT Parameter Parameters for each AOT INSTMODE Instrument operation mode Detailed instrument setup not described in AOT AOTPAR FIS readout mode Telemetry name PACKETID TIMESYS UTC Explicit time scale specification Time system used in this file DATE OBS YYYY MM DDTHH MM SS DATE END YYYY MM DDTHH MM SS DATE REF YYYY MM DDTHH MM SS AFTM OBS double AFTM END double AFTM REF double PIMTIOBS OXXXXXX PIMTIEND OxXXXXX PIMTIREF OxXXXXX Observation start date time Observation end date time Reference time in the Observation DATE OBS in ASTRO F Time DATE END in ASTRO F Time DATE REF in ASTRO F Time DATE OBS in PIM TI 40 bits DATE END in PIM TI 40 bits DATE REF in PIM TI 40 bits Y OM gt Y YY oo FIS 7777_0BS Time stamp PI
38. MTI of the first frame in the file 7 _END Time stamp PIMTI of the last frame in the file 7777_REF On target observation start 690 sec from the observation start file top Note PIMTI is the primary information directly from telemetry AFTI and DATE are from the timing correction based on PIMTI HE HH HH H HH HF OH OF OF H HH Attitude Information at DATE OBS EQUINOX 2000 0000 Epoch of Coordinate RA 320 5533 degree Target position at DATE OBS DEC 23 3325 degree Target position at DATE OBS ROLL 30 553 degree Roll Angle at DATE OBS AA SOL 90 0021 degree Solar avoidance Angle at DATE REF AA EAR 180 2083 degree Earth avoidance Angle at DATE REF AA LUN 210 6821 degree Lunar avoidance Angle at DATE REF TM SAA 1829 sec Duration since last SAA at DATE REF Definition of SAA is different for different detectors SAA region is defined by the glitch rate map observed by the Star Tracker with arbitrary threshold level IRC follows this threshold Shifts of 30 and 60 seconds are applied to FIS SW and LW respectively 60 AKARI FIS Data Users Manual SAT POSX 2903 5528 km Satellite position at DATE OBS SAT POSY 1704 3092 km Satellite position at DATE OBS SAT POSZ 1968 4286 km Satellite position at DATE OBS DAYNIGHT DAY 4 Day night status at DATE REF These files are updated as pointing analysis goes on from On board AOCS gt G ADS gt Pointing reconstru
39. Shutter close data is used for dark current subtraction Currently the Slow Scan tool uses an average value of the data before the calibration lamp CalA see Section 2 1 2 is turned on for 2 minutes during shutter close For the responsivity correction and flat fielding the Slow Scan tool uses by default a flat field built from the PV observations of zodiacal light and cirrus emission The average flux of the 2 42 AKARI FIS Data Users Manual Output V s Output V s Figure 4 2 3 Comparison of the RMS noise for LW and SW detectors when the shutter is open flat and closed dark FFT noise spectrum PFT noise apectrum Frequency Ha Frequency Ha Figure 4 2 4 FFT noise spectra for a 2s integration data of shutter open left and shutter close right minutes calibration lamp in that observations are used In Figure 4 2 5 the data intervals used for the dark subtraction and flat fielding are shown Examples of dark and flat field tables are shown in Figure 4 2 6 Flat fielding with the observation sky data is attempted in the Slow Scan tool option LOCAL_FLAT and often works successfully for flat quiet skies An average responsivity for each wavelength band is corrected with the 2 minutes calibration lamp and the flat field is built from the observed sky 4 2 4 Conversion to surface brightness The conversion from the slope of the integration ramp V s to surface brightness MJy sr is made by using the respons
40. Turn 30s Nei on w cal sequence 802 5 1177 5 Turn 30s Scan_m15 Scan m15 w cal sequence cal_on cal_on Figure 2 2 7 The scan sequence of the AOT FIS01 numbers are in seconds Scan parameters Two numbers are given to define the scan pattern A scan speed and a cross scan shift length A scan speed of 8 arcsec sec balances depth and sensitivity with scan area for data redundancy and is used for photometry of small numbers of sources A higher scan speed of 15 arcsec sec is used to observe larger areas to a slightly shallower sensitivity A cross scan shift length of 70 arcsec is used for point source photometry and 240 arcsec for small area mapping Target position The satellite is operated such that the target position is located at the center of the scanned area Fri Nov 3 16 07 14 2006 Detector ch 10 2 5x105 1 5x10 207812000 000 55781 2500 00 0 813000 000 207813500 000 AF mue Signal ay FIS200608020 Figure 2 2 8 Example of FISO1 in flight data from the PV phase Time series raw signal with pre and post calibration sequences and the three w cal sequences can be seen Version 1 3 September 14 2007 15 2 2 2 FIS02 Slow Scan Observations for Mapping of Large Areas The FISO2 AOT is designed for the mapping of relatively large areas An observation covers a long strip of 1 degree Table 2 2 4 FISO2 summary Fixed parameters Observing Mode Photometry Band N
41. actor K for a black body Temperature K Band N60 WIDE S WIDE L N160 10 3 38 1 84 1 55 1 10 30 1 05 0 89 0 96 0 99 100 0 99 1 15 0 93 0 99 300 1 03 1 32 0 94 0 99 1000 1 04 1 38 0 94 0 99 3000 1 05 1 40 0 94 0 99 10000 1 05 1 40 0 94 0 99 48 AKARI FIS Data Users Manual 4 3 FTS spectroscopy processing FISO3 FTS analysis toolkit is expected to be available very soon Reduction of the FTS mode observa tions will consist of many iterative procedures and trial processing There are various instrument anomalies that have to be settled and corrected for example distortion of the interferogram due to the transient response of detectors Fabry Perot like fringes in the SW spectra due to interferences in the detector etc The current version of the FTS analysis toolkit can not yet be applied to all the FTS observations There remain instrument anomalies which are not considered in the current toolkit and the present calibration is only applicable to a limited subset of the observations In addition the absolute flux is also yet to be calibrated Therefore users are urged to contact the FTS team in Japan via the Helpdesk in order to use the FTS analysis tools Note that without following this route the output of the toolkit may result in incorrect scientific results Joining the FTS team for establishing the analysis toolkit is highly welcomed 4 3 1 Overview The FTS analysis toolkit consis
42. ails 4 2 7 Image processing for multiple pointings A tool is provided within the Slow Scan data reduction toolkit to co add mosaic multiple point ings together The tool may be used for both the co addition of multiple pointings to improve redundancy or to make small maps from multiple FIS AOTs See Cookbook Appendix A for details 4 2 8 Photometric calibration Calibration of scan data The absolute calibration of the FIS Slow Scan data is based on the measurements of the diffuse sky emission from zodiacal light and interstellar cirrus averaged over areas of several Slow Scan observations The absolute brightness is derived from COBE DIRBE measurements The conversion factor from the detector signal I V s to the sky brightness B MJy sr for each pixel is derived as the ratio between the averaged sky brightness level and the averaged detector signal while the calibration lamp is continuously turned on in the calibration sequence data at the beginning and end of each pointed observation The conversion factor is given for different signal levels of the calibration lamp corresponding to selected reset interval R V s My sr Goss etat 421 In the data reduction observation data is first flat fielded by the signal of the calibration lamp assuming that the variation of the detector responsivity is slower than the duration of the observation then the conversion factor is adopted Lea I CTOF 2 ak 4 2 2 I sky we Idark
43. arcsec for LW Note that the grid size is half of the nominal value used by the Slow Scan tool for AOT FISO1 see Appendix A Such a small grid size produces many void pixels and therefore it is not recommended for general purposes Following aperture and sky region are adopted Channel Signal arcmin Sky arcmin SW 2 25 2 25 3 25 LW 3 0 3 0 4 0 Sky level is determined by taking the average of all the available pixels For faint sources these aperture sizes are too large and may introduce contamination from the background Smaller aperture sizes improve the S N of the photometry The aperture correction factor is derived from the curve of growth analysis of the objects as follows Band Aperture arcmin Correction factor N60 0 625 1 58 WIDE S 0 625 1 74 WIDE L 0 750 1 71 N160 0 750 2 03 The measured flux is compared with the expected flux of the sources Asteroids and a star a Boo is used as the primary calibrators Expected fluxes are derived from the TPM model Miller and Lagerros 2002 A amp A 381 324 or stellar SED templates by M Cohen for the Spectral Response of the FIS instrument A colour correction is adopted to convert them to a flat spectrum vF const In addition several infrared luminous galaxies are included in the sample Their fluxes are estimated from ISO observations or their IRAS flux The ratio of the measured flux to the expected flux is fairly constant among the samples and is tabula
44. ark sav FISDR gt help FLUX_DARK DOUBLE Array 4 100 8 Signal level of dark data shutter close signal data pixel dark_data An FISO1 observaton data file contains eight dark measurements and an FISO2 data file has six The meaning of the first dimension is the same as FLUX_CAL FISDR gt restore FIS_SW_20070705213613_1770_flat sav FISDR gt help FLUX_FLAT DOUBLE Array 4 100 Signal level of the flat field data data pixel The meaning of the first dimension is the same as FLUX_CAL MK_TXT_FILE option additionally creates the following text format files The contents of the files are almost the same as those in the sav files They are only left for compatibility and are not recommended to use by the observers FIS_ SW LW _20061225081641_1770_dark_ 0 1 2 txt FIS_ SW LW _20061225081641_1770_cal_ 0 1 2 txt FIS_ SW LW _20061225081641_1770_cal_dark txt FIS_ SW LW _20061225081641_1770_flat txt FIS_ SW LW _20061225081641_1770_flat_dark txt FIS_ SW LW _20061225081641_1770_fit_pr txt FIS_ SW LW _20061225081641_1770_fit_ar txt FIS_ SW LW _20061225081641_1770_ctof txt Co add image processing ss_make_map pro ss_make_map reads the output files of ss_init_proc applies calibration and creates the co add image in various formats The procedure ss_init_proc is called from ss_run_ss with all options Therefore users are not required to use this routine directly 92 AKARI FIS Data Users Manual
45. articular module fails to process data properly or when any data have an anomaly In addition the BAD flag is an OR operation of the other flags see Section 6 1 Therefore the BAD flag can be used for a quick check of data quality For more detailed analysis the individual flags should be inspected Digits to Volt conversion GB_Conv_to_Volt This procedure converts from ADU to a signal in Voltage units The output is stored in the branch FIS_OBS under Detector data Flux of the TSD file see Section 6 1 CRE non linearity correction GB_Ramp_Curve_Corr The output of the cryogenic readout electronics CRE has non linearity characteristics depend ing on the output voltage This function corrects this non linearity assuming that the degree of deviation from an ideal integration ramp curve is a function of output voltage Version 1 3 September 14 2007 41 4 2 Slow Scan processing and calibration FISO1 and FISO2 4 2 1 Detecting glitches of cosmic ray hits Glitches are caused by the effects of cosmic ray particles on the detectors A radiation hit or glitch shows up in the Slow Scan data as an abrupt change of signal 0 1s while celestial sources exhibit a slower time profile 1s Thus in principle it is straight forward to discriminate glitches from a source signal in the time domain SW Detector ch 10 glitch j 1 301 0 A A Sigral ADU A EA MANE EA El Er A EL 1 140x101 142x101 144x101 146x101 14
46. ary mirror temperature K IRC float irc_subref_tmp Secondary mirror temperature K IRC float irc_fpip_tmp1 FPI plate K IRC Version 1 3 September 14 2007 69 Attitude and Orbit Control Unit AOCU extension Outputs of APID AOCU Attitude and Orbit Control Unit is stored in this extension 1 Time double aftime longlong pimtiorg 2 AOCU Status bit status 8 1 2 3 4 blank ao_rom_ram ads_mode_bi ads_mode_b0 5 8 reserved 3 Analog telemetry double aocu_ads_q 4 double aocu_body_rate 3 byte byte byte byte aocu_saab_mode aocu_sbab_mode aocu_saab_win_num aocu_sbab_win_num double ra double dec double roll double d_ra double d_dec double d_roll double crs_off 4 Quality bit quality 8 3 ASTRO F Satellite Time calibrated which is the time since 2000 January 1 00 00 UTC PIMTI counter from original packet AOCS operation status blank 1 ROM mode 1 RAM mode 0 i e the blank bit for the ads_mode_b1 ads_mode_b0 and aodu_ads_q Attitude determination mode AOCU_ADS_MODE bit 1 Attitude determination mode AOCU_ADS_MODE bit 0 Quaternion at boresight Body rate Angular velocity deg s at boresight STT A operation mode STT B operation mode Number of stars in STT A Number of stars in STT B J2000 R A deg at boresight J2000 Dec deg at boresight Roll angle at boresight deg Scan rat
47. b0 Mirror Position bit 0 Ox09 1 9 rstwidelon Reset Wide L on 1 off 0 OXOC 1 10 rstwideson Reset Wide S on 1 off 0 OXOC 1 11 rstn170o0n Reset N160 on 1 off 0 OXOC 1 12 rstn60on Reset N60 on 1 off 0 OXOC 1 13 lwbooston LW BIAS Boost on 1 off 0 OXOE 1 14 swbooston SW BIAS Boost on 1 off 0 OXOE 1 15 lwbiason LW BIAS on 1 off 0 OXOE 1 16 swbiason SW BIAS on 1 off 0 OXOE 1 17 calalon CAL AL LW on 1 off 0 OXOF 1 18 calason CAL AS SW on 1 off 0 OxOF 1 19 calbon CALB BG on 1 off 0 OXOF 1 20 sinalon CAL sin conv AL on 1 off 0 OXOF 1 21 sinason CAL sin conv AS on 1 off 0 OxOF 1 FIS instrument status 22 32 reserved The rstn170on should be renamed to rstn160on historical reasons However we do not change it for 3 Analog Telemetry byte packetid PacketID FIS obsmode 0x00 8 62 AKARI FIS Data Users Manual byte rstcntwidel Reset counter Wide L Ox0A 4 byte rstcntwides Reset counter Wide S Ox0A 4 byte rstcntni70 Reset counter N160 Ox0B 4 byte rstcntn60 Reset counter N60 Ox0B 4 byte calplscntal CAL pulse counter AL Ox0C 4 byte calplscntas CAL pulse counter AS Ox0D 4 byte calplscntb CAL pulse counter B Ox0D 4 byte aderrcntsw SW A D error counter 0x19 4 byte aderrcntlw LW A D error counter 0x19 4 long mposcnt Assigned mirror position Ox1A 0x2F Assigned interpolated frame counte
48. body is present for each data tag In case of an array of structures the corresponding number of values are in the data body For example if the parameter is a 100 element array of structures and one of the tags in the structure is an array of 3 elements the data body will have 300 values first the tag array for the Ist element of the structure then for the 2nd structure see example Syntax define S dims T tagname C A datatype dimension enddefine data T tagname value enddata 76 AKARI FIS Data Users Manual Example define S 2 T tag_cst C uint T tag_arr A double 2 3 enddefine data T tag_cst 100 for the ist structure element 200 for the 2nd structure element enddata data T tag_arr 0 10 2 they are for the 1st structure element 3 5 5 3E 10 6 5 followings are for the 2nd structure element 1e2 1le2 1e2 2e3 2e3 2e3 enddata 6 2 2 List of CCFs Detector properties BADPL Bad Pixel for the LW band BADPS Bad Pixel for the SW band DEADL Dead Pixel for the LW band DEADS Dead Pixel for the SW band CRNRL Detector corners for the LW band wide resp narrow CRNRS Detector corners for the SW band wide resp narrow OFSTL Detector offsets for the LW band wide resp narrow OFSTS Detector offsets for the SW band wide resp narrow RSTAL Reset anomaly for the LW band RSTAS Reset anomaly for the SW band SATUL Saturation level in Volt for the LW band SATUS Saturat
49. bservation The cause of responsivity change could be glitch after effects The default is 10 practically no flagging SCUT Produce individual images per one way scan i e four images are produced for FISO1 observations two roundtrips and two Version 1 3 September 14 2007 87 images for FISO2 observations one roundtrip This option is useful to confirm source detections by comparing independent scans Normal coadded image from all scans is also created Output image files are labeled as _img 1 2 sav amp _img_ 1 2 _ wln fits SL_RMV When this keyword is set the stray light caused by the Earth shine reflected at the telescope baffle is subtracted The stray light component is evaluated by a boxcar filter of 90 seconds width then subtracted from the data MASK_OFF Normally data in the state of Shutter close and CAL ON are masked and do not appear in the output data If this keyword is set the masked data appears in the output data file and the output image For experts and debugging RESP_COR_OFF If this keyword is set the responsivity correction is not performed and the output is the slope of the ramp in units of V s For experts Image plot style options The following options are passed to ss_make_map pro COORD_GRID_ON Display coordinate grid on a JPEG image OUTLINE Produce jpeg image with outline contour CONTOUR_NUM contour_num Number of contou
50. c Duration since last SAA passage at DATE REF km Satellite position at DATE REF km Satellite position at DATE REF km Satellite position at DATE REF day night status at DATE REF number of stars in STT A at DATE REF number of stars in STT B at DATE REF STT A Mode status at DATE REF STT B Mode status at DATE REF Processing History Any length text Version 1 3 September 14 2007 57 Description H FITS basic information data size information SIMPLE T Standard FITS format Fixed BITPIX 16 number of bits per data pixel FIS Binary table 8 Fixed NAXIS O Number of axes FIS O Fixed EXTEND T Extension may be present T Fixed Data type Data creation processing program information FMTTYPE ASTRO F TSD FIS_SW Type of File Format in FITS file Unique name of the data format Keep ASTRO F by historical reason One of FIS_SW TSD FIS_LW TSD FTYPEVER 4 Version of FMTTYPE Version of the file format described in FMTTYPE CNTTYPE FIS_SW Type of data content Data content One of FIS_SW FIS_LW DATE 2006 09 25T09 45 24 File Creation Date File Creation Date CREATOR tsd_bin2dat Data generator program name CRTRVER 1 0 Version of CREATOR Name and version of the program that creates this file FIS tsd_bin2dat PIPELINE fispl ver 1 0 Data Processing Pipeline name name and version
51. ch data are recommended to be discarded in the data reduction process Observations carried out immediately after SAA passage have also been carefully checked but seem to show little difference in quality compared to the data taken in more quiet regions Some observations that were carried out while the spacecraft passes through the polar cap region where many electrons hit the detectors show significant enhancement of glitches although the effect differs from observation to observation and carefully inspection of the data may be required in these circumstances 3 4 Diffuse and Point Source Confusion For a realistic evaluation of the FIS sensitivity external sources of noise in addition to the intrinsic Instrumental noise have to be considered The sky confusion noise is observational dependent and can arise from both the superposition of sources in crowded fields and from extended structures which vary in surface brightness on scales of the telescope and instrument resolution For the FIS instrument the major components are the sky confusion due to the dust emission from irregular interstellar clouds at high galactic latitudes known as the infrared galactic cirrus and the confusion due to the fluctuation of the extragalactic background built up by the superposition of individual faint sources below the resolution of the telescope beam Confusion can cause centroid position shifts and flux uncertainties leading to positional errors and spurio
52. ction for Survey mode STTA NUM 4 number of tracked stars in STT A at DATE REF STTB NUM 4 number of tracked stars in STT B at DATE REF number of tracked stars in the two STT field at DATE OBS STTA MOD TRK STT A Mode status at DATE REF STTB MOD TRK STT B Mode status at DATE REF Status of the STT one of TRK ACQ STB INI_R INI_N COMMENT Any strings HISTORY Any strings END Version 1 3 September 14 2007 61 FIS_OBS extension Here we show the data structure for FIS data 1 Time double aftime ASTRO F AKARI Satellite Time calibrated which is the seconds since 2000 January 1 00 00 UTC longlong pimtiorg PIMTI counter from original packet longlong fistiorg FISTI counter from original packet longlong pimti PIMTI counter interpolated longlong fisti FISTI counter interpolated 2 Status Status information is provided in the telemetry packet Each status is copied from the cor responding bit in FIS_OBS packet All four band s status are included considering possible interference bit status 32 1 creon CRE on 1 off 0 0x09 1 2 shtop Shutter open 1 close 0 0x09 1 3 fwposon FW Position sensor on 1 off 0 0x09 1 4 fwpos_b1 Filter Wheel Position bit 1 0x09 1 5 fwpos_b0 Filter Wheel Position bit 0 0x09 1 6 mposon Mirror Position sensor on 1 off 0 0x09 1 7 mpos_bl Mirror Position bit 1 0x09 1 8 mpos_
53. d cross scan directions respectively SW positions and LW positions are consistent to within 11 arcsec in scan and 23 arcsec cross scan respectively for bright sources 5 5 Pixel position table The current pixel position table is based on simulations Corrections based on in flight data are being analysed 5 6 Projection Currently the FIS images in FITS format have a known problem with projection and the coordinates of the image may deviate from the real position from the image center to the edge This deviation is typically a few arcmin at the corner It is recommended to use the data in the IDL sav file for further analysis of the image data Chapter 6 Instrument Related Data Products In this Chapter we describe the internal structure of the AKARI FIS observation data A set of IDL data interface routines is provided as a part of the data reduction toolkit Those who are interested in modifying or developing data reduction tools are welcome to contact the data reduction team in Japan via Helpdesk for more detailed information 6 1 Time Series Data TSD Overview and structure H Baba I Yamamura A Kawamura S Makiuti H Kaneda T Nakagawa and C Yamauchi 2006 ASTRO F FIS Survey Data Structure 6 1 1 Overview The data consists of header parts and arrays of data record A record corresponds to a sampling of the detector consists of the instrument data and necessary information from other house keeping HK
54. de the fringe pattern is resolved out and an Airy pattern of the Fabry Perot interference is clearly seen The blue lines in the bottom panel are the rms noise level The three lines in the right panel are different measurements and match each other well indicating that the fringe pattern is reproducible 3 5 5 Interference from the Cryocooler It is known that the vibration from the cryocooler interferes with the FTS mirror drive The vibration appears as a change of the mirror scan speed of up to 30 periodically with a frequency of 15 Hz As the detector readout is at a constant frequency this means that the sampling of the interferogram is at inhomogeneous intervals of the optical path As a result the FFT technique cannot be applied The frequency of 15 Hz corresponds to 196 cm 51 um which is outside the wavelength coverage of the FTS Therefore it is expected that the effects of interference will not appear in the observed spectra No clear influence on the resultant spectra has been observed at this stage of the data analysis 3 5 6 Detector position In flight measurements of the relative positions of the SW and LW detectors indicate that the two detectors are not aligned as expected from the pre flight design Three reference positions are newly introduced as an AOT parameter See section 2 2 5 and Figure 2 1 6 Note that the positions for the SW detector Position 1 is not centered on a SW pixel for historical reasons alt
55. e in J2000 R A Scan rate in J2000 Dec Scan rate in roll angle Offset in cross scan direction from Nominal scan path Quality Flag for condition 70 AKARI FIS Data Users Manual Ground based Attitude Determination System GADS extension Results of ground based attitude determination are stored in this extension 1 Time double aftime longlong pimtiorg 2 Status bit status 8 T blank 2 8 reserved 3 Analog telemetry double double double double double double double double double double double double double double attitude 4 attitude_er 3 angl_vel 3 ra dec roll d_ra d_dec d_roll el_sol aa_sol aa_ear aa_lun crs_off 4 Quality bit quality 8 ASTRO F AKARI Satellite Time calibrated which is the time since 2000 January 1 00 00 UTC PIMTI counter from original packet Satellite attitude status blank 1 Quaternion at boresight Estimated error of position Body rate Angular velocity at boresight J2000 R A deg at boresight J2000 Dec deg at boresight Roll angle at boresight deg Scan rate in J2000 R A Scan rate in J2000 Dec Scan rate in roll angle Solar elongation Solar Avoidance Angle Earth Avoidance Angle Lunar Avoidance Angle Offset in cross scan direction from Nominal scan path Quality Flag for condition Version 1 3 September 14 2007 71 Pointing Reconstruction PR exten
56. el data Co add images are created from the scan data The positions of every pixel at every data point in the scan data are calculated from the boresight position given in the data file and the offset between the boresight and the detector pixels Optical distortion of the detector arrays from the pre flight simulation is taking into account in the pixel position table Fine tuning of the alignment between the boresight to the arrays are carried out from the observation data An image plane of appropriate grid size is prepared and signals from the data points are summed up and then averaged over the number of data points per pixel By default a pixel size of 15 arcsec and 30 arcsec are adopted for the SW and LW data in the FISO1 mode The pixel size is doubled for the FISO2 mode The image grid positions are of simple equal pitch in local sky Currently no projection to the world coordinate system WCS is considered Therefore the FITS format output of the resultant image has a deviation from the real position towards the periphery of the images It is recommended to use the image and coordinate information packed into the provided IDL sav file for further analysis Proper projection will be considered in a near future version of the toolkit By default all available data are accumulated on the image plane An option SCUT produces Version 1 3 September 14 2007 45 images per individual one way scan See the Cookbook Appendix A for more det
57. ened lL Figure A 3 1 TSD file opened with FISv In the two windows labeled X axis and Y axis appear all the extensions contained in the TSD file that can be visualized using the Header View button and the items under the extension FIS_OBS Any of these items can be plotted against one another by selecting the appropriate entry in the corresponding X and Y axis windows A Preview graph appears as is shown in Figure A 3 2 Version 1 3 September 14 2007 95 x FIS Data Visualizer File Main Tools Pipeline Help o al al home2 everdugo FIS_data_reduction data FIS20060802053000_1800_1w fits gz LW Detector ch 10 Samples Gy FIS_OBS Peon Gy Time 3 FISTIORG f E PINTI E how SY FISTI J Status J Analg Telemetry a Q Analg Telemetry Detector Data noxo 0 2 078113x10 Header View Plot All i Image of det Masked Plot 4 Detector Data ey Flags Quality 3 1 Counter Y __ Plot Table Print GB Cnv2 GB Diff GB Batch GB FlagBad c ISAS JAXA AKARI FIS Data Visualizer Ver 3 13 for TSD4 fhome2 everdugo F 1S_data_reduct ion data F1520060802053000_1800_lw fits gz has been opened MSAFTINE Y VDET10 Figure A 3 2 Detector 10 signal plotted against AKARI satellite time Output options include Plot The currently displayed graph image can be plotted by clicking on the action button
58. ersion 1 3 September 14 2007 83 GRID_SIZE DOUBLE 0 0041666667 grid size of the image MAP_MEAN DOUBLE Array 2 4 Information of the image data MAP_MEAN O WIDE band MAP_MEAN 1 NARROW band MAP_MEAN 0 Average sky level 3 sigma clipped MAP_MEAN 1 Standard deviation of sky level MAP_MEAN 2 Number of sky data points HDR STRING Array 27 FITS header strings A 2 2 Available options for ss_run_ss ss_run_ss has many options for selecting the data reduction calibration methods as well as to control its functions Process flow control INIT Stop after ss_init_proc completed MAP Run only ss_make_map module Data should have been processed by ss_init_proc with INIT option This allows different options of ss_make_map to be tested without running ss_init_proc every time SW LW Process only SW LW data Input Output file names TAG_NAME tag_name Add a specified string to the output file names For example tag_name _new will make the output file names as FIS_ SW LW _20061225081641_1770_new_img_ w n fits FILE_INPUT The first argument of ss_run_ss is a file name instead of directory name CUBE_FITS Generate image cube fits containing image error and density maps in a FITS file instead of three independent files The output file names are _cube_ w n fits Selection of positional information 84 AKARI FIS Data User
59. es the spectra of most pixels can also be reproduced to within 10 in wavenumber for those pixels less affected by fringes Version 1 3 September 14 2007 37 3 5 4 Fringes The SW channel suffers from strong fringes in the spectra Figure 3 5 22 shows an enlargement of the fringe patterns in the Full Resolution mode and the SED mode respectively The cause of the fringes is thought to be a reflection within the detector element by the parallel surface of the chip therefore it should also present in the photometric mode Throughout the laboratory measurements the fringe pattern remains at the same position implying that it can be easily removed The fringe pattern looks quite similar for different in flight observations The largest fringe component can be significantly reduced by applying a predefined model pattern Further investigation is ongoing to remove the residual fringes However observations of sharp lines on the fringe shoulders will require special care 0 0015 E 0 001 0 001 T T T T 0 001 J 0 0008 0 0008 0 0008 0 001 E L 0 0006 0 0006 0 0006 lt u19 998 A V sec em W19 99S A 4 0 0004 gt 0 0004 4 0 0004 V sec cm 0 0005 J 0 0002 0 0002 0 0002 90 92 94 96 98 100 110 112 114 116 118 120 Wavenumber cm Wavenumber cm Figure 3 5 22 Fringe pattern of the FTS spectra in Full Resolution mode left and SED mode right In Full Resolution mo
60. etween 50 and 180 um two broad bands and two narrow bands Individual detector systems are implemented for the two short and two long wavelength bands respectively The FTS covers the entire FIS wavelength range with a resolution of 0 36 cm R 450 150 or 2 4 cm R 75 23 Table 2 1 1 Hardware Specifications of the Far Infrared Surveyor FIS Photometric mode Band N60 WIDE S WIDE L N160 Wavelength Range um 50 80 60 110 110 180 140 180 Central Wavelength um 65 140 160 Band Width um 21 7 7 9 52 4 34 1 Detector Monolithic Ge Ga Stressed Ge Ga 0x2 5x3 15 x 2 2 0K 2 0K 26 8 44 2 es Array size Operational Temperature Array size 20x2 Pixel size arcsec Pixel pitch arcsec NO o a Aa Ne E Readout Capacitive Trans Impedance Amplifier CTIA Spectroscopic mode Martin Puplett type Fourier transform spectrometer 50 110 The detector responsivity is higher than 20 of the peak 2 As defined by the bandwidth equation below 3 The SW detector was manufactured by NICT 4 The values may change as more accurate telescope parameters become available The Central Wavelength is given to be a representative number of the band near the weight center of the band profile The band width is then defined by the following equation for a flat spectrum vF const Ape fruT 1 E v dv 2 fr P dv v 2 1 1 r v T Ve Fy ve r ve T Ve Ve Together the responsivity r and optical trans
61. f correction factor difference between corrected and the original data 33 gb_set_glitch_status_gp gb_set_glitch_status_gp 33 gt correction after glitch detection 19 20 qual_gpgl_corr correction of glitch tails for Gaussian processing method 21 22 qual_mtgl_corr correction of glitch tails for Median transformation method 3 gb_transient_corr 23 24 qugl_tr_hist history information availability 25 26 qual_tr_param correction parameter availability gb_dark_subtraction make_dark_table 27 28 qual_dk_data quality of the dark data in one shutter close 29 30 qual_dk_param availability of the data of a shutter close to derive a dark value 31 32 qual_dk_table quality of the dark values of the correction Version 1 3 September 14 2007 65 table fluctuation etc 33 gb_flux_calib 33 34 qual_fx_corr availability of calibration parameters 35 36 qual_fx_param error in calibration factors 37 40 reserved 7 Counter short cnt_saa NDET time in seconds since the last SAA passage tm_saa is used in SE extension duration since the last corresponding glitch GP short cnt_glitch_gp NDET duration since the last corresponding glitch MMT short cnt_glitch_mt NDET 66 FIS_HK extension AKARI FIS Data Users Manual Outputs of APID FIS_HK which contains some minor status of FIS are stored in this ex tension 1 Time double aftime lon
62. f FISO1 amp FISO2 Photometry imaging observations by the FIS in pointed observation mode is always carried out with the Slow Scan operation At the moment the performance of Slow Scan mode has not been systematically evaluated because of various technical problem on the calibration and data reduction Therefore the performance given in this section are estimated by scaling the All Sky Survey detection limits by factors which are functions of the scan speed and the reset interval However because of the nonlinear responsivity transient effects and other complicated characteristics of the instruments the scaling law is not always straightforward Table 2 2 5 lists the sensitivities for the three scan speeds incorporated into these 2 FIS AOTs Note that confusion is not included in these estimates The numbers in the table are 50 noise levels for a single scan In principle the sensitivity should increase as the inverse square root of the number of scans such that four scans in FISO1 should improve the detection limit by factor of 2 On the other hand this redundancy can alternatively be used to increase the reliability of the results In such a case the detection limit remain unchanged We leave this at the discretion of the user As the standard rule of thumb we propose to apply the numbers per one round trip scan So for FISO1 which carries out two round trips a sensitivity of 1 2 of the value in the table can be assumed Following
63. glong pimtiorg 2 Status bit status 8 1 2 blank_subcom_data blank 3 8 reserved gt E El gt 2 ASTRO F AKARI Satellite Time calibrated which is the time since 2000 January 1 00 00 UTC PIMTI counter from original packet Satellite attitude status blank 1 blank bit for subcom data for sw_heater_tmp Note that some FIS status are stored in the HK_2 extension 3 Analog data byte byte byte byte byte byte long byte fis_fw_f_pul fis_fw_r_pul fis_lw_wire_light fis_run_mode fis_obs_mode fis_asq_pattern fis_asq_step sw_heater_tmp Filter wheel pulse counter Forward Filter wheel pulse counter Rewind LW wire light DAC set value RUN mode Observation mode ASQ pattern ASQ step SW heater temperature Version 1 3 September 14 2007 IRC_HK extension 67 Outputs of APID TRC_HK which contains status of temperature of the focal plane instru ments are stored in this extension 1 Time double aftime longlong pimtiorg 2 IRC status bit status 8 1 blank 2 8 reserved 3 Analog data TBD we we we ASTRO F AKARI Satellite Time calibrated which is the time since 2000 January 1 00 00 UTC PIMTI counter from original packet Status of IRC functions which may cause interference Data blank Details TBD with IRC team 68 AKARI FIS Data Users Manual HK_2 extension Outputs of APID HK_2 which contains bas
64. he FIS detectors is influenced by cosmic ray hits The induced glitches in the detector signal at a frequency of about of approximately one per minute contributes to the final noise figure After such hits the noise increases by a factor of a few for around ten seconds This degrades the S N ratio worse than the values listed in Table 2 2 5 Therefore 18 AKARI FIS Data Users Manual we recommend for observers to repeat scans several times in order to obtain good sensitivity close to the limits in Table 2 2 5 The performance of the LW bands Stressed Ge Ga detector array is particularly worse than pre launch prediction This is attributed to two factors Before launch we expected that the responsivity should increase at least by a factor of two in space as observed in the case of IRAS ISO IRTS and Spitzer However after launch the bias voltage had to be reduced in order to avoid unstable behavior As the result of this the responsivity is now nearly equal to that on the ground and the detection limit has correspondingly been degraded compared to the pre launch expectations In addition to this it was assumed before launch that the noise of the LW channels would depend on the integration time as the power of t71 that is S N tt based on the ground test results However after launch the observed noise of LW arrays instead was found to follow a dependence of on the time as t 2 that is S N 171 2 As the result of these two factor
65. hough the absolute pointing accuracy may be is as large as the pixel size Chapter 4 Data processing FIS observations taken in All Sky Survey Mode are processed by means of the AKARI FIS Survey Data Reduction Pipeline For the Pointed Observations Slow Scan mode a dedicated toolkit is provided to the users The toolkit is still evolving and users are recommended to check the updates Currently the distributed files contain the raw data and example reduction results jpeg image to give users a first impression of the data Although they are fully reduced data it must be emphasised that the processing is done in an automatic way using the default options of the Slow Scan tools which does not involve any scientific judgment Instructions of how to use the FIS Slow Scan tool Cookbook are given in Appendix A 38 Version 1 3 September 14 2007 39 4 1 AKARI All Sky Survey ASS Pipeline The AKARI All Sky Survey Pipeline can be divided into three steps 1 construction of FITS datasets from telemetry data 2 the scan processing and calibration Green Box and 3 con firmation source extraction and catalog production ASTRO F FIS Data Reduction Team 2001 Sept 4 The ASTRO F FIS survey data reduction The Pipeline Design and the Calibration Strategy 4 1 1 Out line of the data flow The pipeline Green Box modules process and calibrate the time series data TSD see Sec tion 6 1 The procedures included are see
66. iation and FFT e A subset can be made from the TSD interactively The current TSD will then be replaced by the subset e Plots can also be masked by some of the defined flags e Signal processing can be carried out by calling the GB pipeline modules see Chapter 4 However FISv is not intended to be at the moment a data reduction tool It should be noted that using GB pipeline functions will override the original processing of the data A history of the GB modules used is kept in the primary header of the TSD file 100 AKARI FIS Data Users Manual A 4 Contribution tools Contribution tools are extra tools which provide additional functions to the standard processing package or tools for data reduction analysis beyond the scope of the standard tool A 4 1 Making mosaic images from multiple observations Program Name SS_mosaic_image pro Developers M Shirahata and S Matsuura ISAS Purpose This tool is prepared to make mosaic images map using multiple scan data It is useful for observations of wide area covered by multiple pointings and deep imaging by repeating the pointed observations Calling Sequence ss_mosaic_image targetdir SIGMA sigma T_START t_start T_END t_end GRID_SW grid_sw GRID_LW grid_lw LON_CENTER lon_center LAT_CENTER lat_center LON_SIZE lon_size LAT_SIZE lat_size ECLIPTIC ecliptic GALACTIC galactic CUBE_FITS cube_fits TAG_NAME tag_name aot_mix aot_mix
67. ic data of Cryostat FIS and IRC should be stored in this extension 1 Time double aftime ASTRO F AKARI Satellite Time calibrated which is the time since 2000 January 1 00 00 UTC longlong pimtiorg PIMTI counter from original packet 2 Cryostat FIS IRC status bit status 16 CRYO FIS status 1 blank blank 1 2 blank_cryo_temp_data blank bit for Cryo temperature data 3 4 reserved 5 cryo_temp_data_en_ds Cryo temperature data enabled disabled 6 reserved 7 fis_cpu_run_rst FIS CPU run reset 8 fis_fis_on_off FIS on off 9 fis_tmp_pol_pos_neg Thermometer polarity 10 fis_obs_seq Observation sequence start stop 11 fis_rsw_auto_cmnd Auto periodic reset mode on off 12 fis_fcal_frq_b1 CAL overlay sine wave frequency Bi bit 1 13 fis_fcal_frq_bO CAL overlay sine wave frequency B1 bit 0 14 reserved 15 irc_cpu_ru_rs IRC CPU run reset 16 irc_irc_on_of IRC on off 3 Cryostat temperature float cryo_he_tank_1 He tank 1 temperature K one close to heat strap float cryo_baffle_1 Baffle 1 temperature K one close to the tel float cryo_baffle_2 Baffle 2 temperature K 4 Cryostat current float cryo_cold_hd_a_dr_i Cold head A driving current A float cryo_cold_hd_b_dr_i Cold head B driving current A float cryo_comp_a_dr_i Compressor A driving current A float cryo_comp_b_dr_i Compressor B driving current A 5 IRC Analog data float irc_mainref_tmp1 Prim
68. instruments as well as positional information given by the ground station Usually the sampling rate of HK data is much slower than that of instrument data These information are regridded by a suitable method e g interpolation to synchronize with the clock of the target instrument The data for individual instruments or source of information are each maintained in a separate unit known as a branch TSD data are examples of these branches In the TSD data structure all data are related to each other by a time stamp The reference time stamp throughout the data is called the Key Time and is given by the main instrument FIS detector readout timing The Key Time is copied to other branches and data from the instruments are regridded to it All information from the main instrument is included in the TSD dataset while only the subset of any information that is needed for the data reduction is provided from other instru ments 6 1 2 Physical file format of TSD The physical file format of the TSD to exchange the data is the FITS Binary Table Extension In the table each row corresponds to a sampling which is identified by PIM TI the clock counter provided by the DHU Data Handling Unit of the spacecraft For the detailed information about FITS Binary Table Extension see section 8 3 Binary Table Extension in Definition of Current FITS Standard NOST 100 2 0 1 Size of one TSD file for a single pointed observation is
69. ints with shutter close DRV_MASK_TOT INT Array 3542 Number of data points with calibration lamp is ON or shutter is closed per ramp If not zero the ramp does not contain sky observation data Q_MEAN DOUBLE Array 4 3542 Quarternion averaged over each ramp AA_MEAN DOUBLE Array 3542 Earth Avoidance Angle EAA averaged over each ramp AOT STRING P12_FIS01 AOTPARAM STRING 0 5 8 70 DATA_TYPE STRING FIS_SW Information about the observation N_INT INT 1 Value given by N_RAMP_DIV option 1 default data point corresponds to each ramp RST STRING 05N Internal status to identify the reset mode RST_INT DOUBLE 0 47468354 The actual reset interval in seconds AOCU_ADS INT 0 Version 1 3 September 14 2007 91 GLITCH_RMV_OFF INT 0 RAMP_COR_OFF INT Options for ss_init_proc pro 1 ON _cal sav _dark sav _flat sav contains calibration information FISDR gt restore F1S_SW_20070705213613_1770_cal sav FISDR gt help FLUX_CAL DOUBLE Array 4 100 7 Signal level of calibration lamp data data pixel cal lamp_data An FISO1 observaton data file contains seven calibration lamp data and an FISO2 data file has five 0 Pixel index 1 Average calibration lamp strength V s 2 Uncertainty of the averaged value rms sqrt N 1 3 Number of data samples N FISDR gt restore FIS_SW_20070705213613_1770_d
70. ion level in Volt for the SW band Calibration C2VT Threshold for conversion to Volt from ADU FLATL Ratio of A Cal flat source and error for the LW band FLATS Ratio of A Cal flat source and error for the SW band RCTBL Ramp curve correction table flight preliminary for the LW band RCTBS Ramp curve correction table flight preliminary for the SW band SIGJL sigma_j estimated from fis20050219_031354_04_lw SIGJS sigma_j estimated from fis20050219_031354_04_sw V2FL Scaling factor from Volt to Flux Constants GLGP Parameters for various Glitch Processing modules Appendix A FIS Slow Scan Toolkit Cookbook In this section we describe how to use the FIS Slow Scan data reduction toolkit provided from the project team This software tools are often globally referred to as the fisdr system A 1 Installation A 1 1 Prerequisites The toolkit is currently developed under IDL version 6 3 6 4 It may work with IDL versions as early as 6 0 but it is not guaranteed The toolkit does not support earlier versions of IDL It has been reported that the software works under the Linux Redhat Fedora CentOS Vine MacOS 10 4 and Windows XP environments At least 512 MB of free memory space is required to process the Slow Scan data A computer with 1 GB or more memory is recommended The toolkit uses the IDL Astronomy Library http idlastro gsfc nasa gov The routines contained in this library are often updated Therefore they
71. irror Position sensor on 1 off 0 0x09 1 7k Mirror Position bit 1 0x09 1 mermada Mirror Position bit 0 0x09 1 element name 9l Reset Wide L on 1 off 0 Ox0C 1 10 Reset Wide S on 1 off 0 Ox0C 1 11t rstni70o0n Reset N170 on 1 off 0 Ox0C 1 121 rstn60on Reset N60 on 1 off 0 Ox0C 1 13 lwbooston LW BIAS Boost on 1 off 0 OXOE 1 14t swbooston SW BIAS Boost on 1 off 0 Ox0E 1 15t lwbiason LW BIAS on 1 off 0 OxXOE 1 16t swbiason SW BIAS on 1 off 0 OxXOE 1 17t calalon CAL AL LW on 1 off 0 OXOF 1 18t calason CAL AS SW on 1 off 0 OXOF 1 19t calbon CALB BG on 1 off 0 OXOF 1 20t sinalon CAL sin conv AL on 1 off 0 OxOF 1 21t sinason CAL sin conv AS on 1 off 0 OxOF 1 22 32 reserved Figure 6 1 2 An example of status section 6 1 6 TSD detailed description Primary Header string FMTTYPE Type of Format in FITS file integer FTYPEVER Version of FMTTYPE string CNTTYPE Type of data content string DATE File Creation Date string CREATOR Data generator program name 56 string string string string string string string string string string integer integer integer string double double string string string string string string string double double double string string string double double double double double double double double double double double string integer integer string string st
72. its gz FIS_LW_20061225081641_1770 jpg FIS_SW_20061225081641_1770 jpg README WARNING You may want to preserve the jpeg files as they are overwritten during the pro cessing Start up fisdr and run ss_run_ss with the default setup fisdr IDL gt ss_run_ss AKARI_FIS_1234567_001 AOCU The program will search for all the FIS data FIS_ SW LW _ fits gz in the specified directory and will attempt to process them The option AOQCU is needed if you want to compare your results with the sample jpeg files see Section 5 4 See below for more details on the different running options You will see some plots and images in different plot windows If the processing completes without error the program will produce several output files in the directory Input data FIS_ SW LW __20061225081641_1770 fits gz Intermediate files FIS_ SW LW _20061225081641_1770_ar sav FIS_ SW LW _20061225081641_1770_pr sav FIS_ SW LW _20061225081641_1770_cal sav FIS_ SW LW _20061225081641_1770_dark sav FIS_ SW LW _20061225081641_1770_flat sav 82 AKARI FIS Data Users Manual Output result files FIS_ SW LW _20061225081641_1770_img jpg FIS_ SW LW _20061225081641_1770_img sav FIS_ SW LW _20061225081641_1770_img_ wln fits FIS_ SW LW _20061225081641_1770_err_ wln fits FIS_ SW LW _20061225081641_1770_num_ wln fits with CUBE_FITS option the following files are created instead of _img _err _num files FIS_ SW LW _200612250
73. ivity correction table The responsivity correction table is calculated as the ratio between the calibration lamp signal and the signal of celestial flat sources comprised of the zodiacal light and cirrus emission observed during the PV phase see Section 4 2 8 for details Version 1 3 September 14 2007 43 Detector signal Detector signal meno 1 5x10 Dark Status ColASOn 0 1x10 2x10 3x10 4x10 o 1x10 2x10 3x10 4x10 Figure 4 2 5 Sequence of FISO1 and FIS02 observations with the corresponding flags for shutter close red and CalA on blue In bold red numbers the average value during shutter close used as the dark measurement is shown In bold blue numbers the average value used for responsivity correction when the calibration lamp is on CAL Note that CalASOn status turned on every minute pulses but there is no signal on the detectors as the current of the calibration lamp is set to 0 AS CAL signal V s AL CAL signal V s 0001 Figure 4 2 6 Examples of dark and responsivity tables 4 2 5 Background offset subtraction Only the instrumental thermal background inside the FIS entrance shutter is subtracted during the default processing Stray light due to Earth shine reflected at the telescope baffle is then the major internal contribution to the observational background see Section 3 1 6 For point sources the background subtraction can be performed by median filte
74. lanned to be corrected empirically by tables comparing the signals for the instantaneous and continuous flux levels 0 003 i 0 006 y r SW 17ch LW 11ch 0 0025 0 005 S S 0 002 L 0 004 L l m il iil i 2 2 5 5 20 0015 20 003 x amp S S 2 0 001 E 0 002 funeral ne jo 0 0005 L 0 001 o 20 400 600800 1000 1200 00o 200 300 400500 600 700 800 sampling 24Hz sampling 16Hz Figure 3 2 15 Examples of transient response for the FIS detectors for a step wise change of the incident flux Version 1 3 September 14 2007 31 1 SW ch 2 5 sec e LW ch 5 5 sec cal yt 0 0026 4 f 0 002 ilse cal oo Pulse cal a Pulse cal 0 0015 t tiro Aferertial output V diferential output V E a i Xe ne ro na mx o A 0 0005 0 0005 0 4 o 1 4 4 23800 2000 24200 24400 24600 24800 25000 25700 25400 25600 16000 16200 16400 10600 16800 17000 sampling 24 H sampling 16Hz Figure 3 2 16 Transient response to pulse irradiation On the left side of the each figure the calibration lamps are flashed at very short periods simulating the passage of a point source in the All Sky Survey While on the right the lamps are turned on continuously for 5 sec The intensity of the calibration lamps was the same for both cases Although 5 sec is not enough time for the detectors to reach a constant output level it is obvious that the output signal for flashes is smaller than that
75. layout of the FIS detectors Detector Readout Modes The readout circuit of the FIS is a Capacitive Trans Impedance Amplifier CTIA The signal from each pixel is accumulated in the capacitor as the detector observes far infrared photons The voltage at the capacitor is then read out at appropriate intervals The charge level in the capacitor is periodically reset in order to avoid saturation The accumulated signal between two resets is called a Ramp Differentiation of the Ramps provides the data that should be proportional to the flux of the incoming radiation The reset operation of the FIS detectors 2The SW detector was manufactured by NICT Version 1 3 September 14 2007 9 is synchronous i e resets are inserted with a set time interval regardless of the signal level of each pixel Although the reset interval is carefully optimized to maximize the instrument performance bright objects passing through the FIS FoV will possibly cause saturation of the detector signal Three different detector readout modes are considered Simple sampling mode is the basic operation sequence Each sampled signal is downlinked to the ground after A D conversion This mode is used for the FTS observations Co add Nominal mode samples the ramps at a higher rate then the sums of every n sam plings are transfered to the ground This can reduce the noise by a factor of yn while preserving the data size n is fixed as 6 in the current design The Co
76. le sat_posx double sat_posy double sat_posz ASTRO F AKARI Satellite Time calibrated which is the time since 2000 January 1 00 00 UTC PIMTI counter from original packet Satellite attitude status blank 1 Data type Prediction Determinated Day Night in SAA region in Polar region seconds since last SAA passage lt 0 during the passage Clock start at end of Bias Boost Satellite position in Earth reference frame Satellite position in Earth reference frame Satellite position in Earth reference frame Version 1 3 September 14 2007 73 6 2 Calibration Constant Files CCF Calibration Constant Files CCF contain either correction factors or instrumental parameters necessary to e steer the processing e to remove or to correct for instrumental effects in the data and e to carry out the flux calibration In this section detailed descriptions are given of the structure and contents of the CCF files Note that users do not have to deal with the CCF files directly unless they explicitly wish to change the calibration 6 2 1 CCF Structure A CCF file contains one set of parameter s i e a constant an array or a structure variable Multiple values are packed in IDL type structures A CCF file consist of a header part a data definition part and one or more data body part s Header starts with 4HEADER and end at FENDHEADER Data type definition starts with DEFINE
77. m and gt 120 cm respectively SW33 The sensitivity for the line emission is estimated from diffuse bright regions towards the Galactic center For C II 158 um and O III 88 um in LW30 and SW15 respectively the 50 detection limit is estimated to be 7 3 x 1078 and 8 0 x 10 7 Wm sr respectively Considering the relative sensitivity among different pixels Fig 3 5 20 and the estimate that the PSF in spectroscopic mode is larger by 20 than that in photometry mode section 3 1 these correspond to 50 detection limits of 3 x 10715 W m and 5 x 10714 W m for C II 158 ym and O III 88 um respectively with the AOT position parameter 0 If the reset anomaly is not correctly interpolated it produces artificial features at the corre sponding wavenumber Table 2 2 8 lists the possible wave numbers which are affected by these artificial features Table 2 2 8 The list of the possible wave numbers affected by artificial features caused by reset anomaly Reset interval sec Wave number affected by the reset structure em SED mode 96 9 193 8 48 4 96 9 145 4 193 8 24 2 48 4 72 7 96 9 121 1 145 4 169 6 193 8 12 1 24 2 36 3 48 4 60 6 72 7 84 8 96 9 109 0 121 1 133 2 145 4 157 5 169 9 181 7 193 8 Full Resolution mode 93 1 186 2 46 5 93 1 139 6 186 2 23 3 46 5 69 8 93 1 116 4 139 6 162 9 186 2 11 6 23 3 34 9 46 5 58 2 69 8 81 5 93 1 104 7 116 4 128 0 13
78. m before the beam becomes confused 34 AKARI FIS Data Users Manual Table 3 4 2 Estimated confusion limits due to galactic cirrus in AKARI FIS bands assuming the model of Helou amp Beichman 1990 The tabulated FIS sensitivity is the 50 limit for a single Slow Scan with a 2 second integration and scan speed of 15 arcsec s Band Sensitivity Confusion Limit 50 mJy for lt B gt 50 mJy 0 5 MJy sr 3 MJy sr 10 MJy sr N60 78 0 37 5 49 33 WIDE S 16 0 77 11 68 WIDE L 85 3 6 54 330 N160 198 4 3 63 388 of 1 20 sources per beam 20 beams per source Table 3 4 3 tabulates the source confusion limit assuming the above criteria for the FIS bands From the table it can be seen that source confusion will only become problematical in the WIDE FIS bands Table 3 4 3 Estimated confusion limits in mJy due to point sources for AKARI FIS bands The tabulated FIS sensitivity is the 50 limit for a single Slow Scan with a 2 second integration and scan speed of 15 arcsec s 5 o Sensitivity mJy Source Confusion Limit mJy Band Slow Scan Mode 20 beam source N60 78 3 WIDE S 16 7 WIDE L 85 45 N160 198 50 Version 1 3 September 14 2007 35 3 5 ETS mode 3 5 1 Transient Effects on the FTS data In the FTS mode the detectors have to observe a rapidly changing signal from the interferogram Naturally strong transient effects appear in the output signal Figure 3 5 19 plots the interfer ograms corresponding to the forward and backward motio
79. mittance T define the system responsivity R the relative spectral response function RSRF 6 AKARI FIS Data Users Manual 2 1 2 Optics and Filters The FIS Optics Figure 2 1 1 shows the bottom view looking out of the telescope telescope and the sky are into the page from the FIS instrument The light path is indicated by the dash dotted arrows Optical elements are labeled There are three moving parts a shutter at the light entrance a filter wheel and the moving mirror of the FTS The filter wheel can be rotated to switch between photometric and spectroscopic FTS modes The shutter will be closed occasionally to obtain instrumental dark levels Blocking Filters 0 300cm amp 430cm 1 Collimator Mirror Bending Mirror 100mm yf Yf Input Aperture with shutter Black Body Source Y Y gt HO Movable Roof Top Mirror gt UK P Hole or Input Polarizer i DS J gt Calibration Sources Beam Splitter Polarizer Dichroic Beam Splitter 6 91cm Fixed Roof Top Mirror A A OW SPECTROMETER EN Low Pass Filter o 90cm Low Pass Filter o 70cm or Output Polarizer Camera Mir mera Mirror Low Pass Filter o 220cm High Pass Filter o 133cm Short Wavelength Detector Weight 5 5kg Long Wavelength Detector Ge Ga 2 2K stressed Ge Ga lt 1 8K Figure 2 1 1 The optical paths within the FIS Locations
80. ms of the signal in the time domain FFT Other display functions allow the display of all the pixels see Fig A 3 9 and the display of a 2D and 3D image of the detector array Fig A 3 10 VDET LIST FIS20060802053000_1800_lw fits gz LW Detectar ch 3 ils LW Detectar ch 1 LW Detectar ch 2 Close Data DET w FLUX Ymin ara A 182x104 152x101 1 52x10 Irex Irex Iridex LW Datactor ch 17 LW Detector ch 1B LW Detector ch 19 J Ymax J Xmin J Knax 30010 1 aaa naia Irex Irex Iridex LW Detector ch 31 LW Detactor ch 32 LW Detactor ch 33 LW Detactor ch 34 ReDraw J 3 ly 3 D4x10 1 52 10 152x104 x Irrdex a I Irex LW Datactor ch 49 LW Datactor ch 46 LW Detactor ch 47 Figure A 3 9 Signal plot of all pixels Version 1 3 September 14 2007 7 FIS Detector Image la Color range Hax l 7550 Mins I 4319 Speed sec frm i 0 1 2 DET y FLUX 3D Color range Hax 7550 ih H 4319 Speed sec frm 041 gt g w FLUX To stop playing drag the slide bar to the right end Close Play To stop playing drag the slide bar to the right end Close Figure A 3 10 2D and 3D images of the detector array A 3 3 Main functions Processing 99 FISv also allows some simple calculations and processing besides the mentioned statistics dif ferent
81. n of the mirror Large deviations are seen Correction of transient effects in the FTS data is being investigated forward backward V sec 0 1 0 05 0 0 05 0 1 Optical Path Difference cm forward backward V sec A cae ame ae A EE SR Om COE NT OR Me ee Veter se cee 0 15 0 1 0 05 0 0 05 0 1 0 15 Optical Path Difference cm Figure 3 5 19 Comparison of forward blue and backward red interferograms The difference between the two interferograms is thought to be due to detector transients 3 5 2 Detector Response Inhomogeneity As described above pixels in the detector arrays do not have a uniform responsivity Fig ure 3 5 20 indicates the relative responsivity variation of the detector pixels in the FTS mode integrated over an effective wave number range of 85 160 cm for the SW array and 65 85 cm for the LW array The relative responsivity of most of the pixels are within 40 for the SW array however the pixels of the LW array have larger variation There are several pixels with extremely high responsivity e g SW pixel 23 and LW pixel 31 The wavenumber dependence of the responsivity also differs from pixel to pixel which should be calibrated as the spectral correction factor in the analysis tools see section 4 3 In the LW detectors there is also a variation in the wavelength profile long wavelength cut off 36 AKARI FIS Data Users Manual Normalized responsivity o a T T ii
82. ndow to center plot on the page Bits Per Image Pixel 8 Directory home2 everdugo FIS_data_reduction reduction Setups None pa Filename idl ps F European Style Browse Figure A 3 6 Postscript output setup dialog Processed data can also be saved into another TSD file FITS binary A 3 2 Main Functions Display As shown in the previous section it is possible to display detector signals for each pixel and the status Shutter open closed calibration lamp on off etc More than one value can be plotted at once by selecting multiple items using the Ctrl or Shift key on your computer keyboard They will be plotted in the same graph as shown in Figure A 3 7 where the detector signal and Shutter Open status ShtOp are selected E Fisv Plot Window F1520000802053000_1800 Iw fits gz EIEE 3 Symbol Grid Double Y uo al al Print es star irr sFlea Fr Close Figure A 3 7 Detector signal and Shutter Open plot The button SFlag on the plot window allows both keywords to be displayed separately on a Double Y axis as shown in Figure A 3 8 98 AKARI FIS Data Users Manual 4 Symbol Grid aa a a Print PS STAT DIFF FFT Close Figure A 3 8 Detector signal and Shutter Open plotted separately using the SFlag option The plot window also allows one to perform simple statistics STAT differentiation DIFF and Fast Fourier Transfor
83. nsient effects o 51 5 2 Straylight correction s a soe ess aoe dani aa e a aa ee 51 5 3 Photometric calibration sanes ea aoe ee i a a A T 51 bdck Scan speed 2 roos neuian a Be wank A A a A 51 Dd Zo Calibrators 2 205 aio Sah AR o Eh A EA E 51 5 4 Attitude Determination During the Pointed Observations 52 5 5 Pixel position table e s soes 43 ee ke a a a ee eS 52 oO Projections rar bce td alas a Ge A me een She bbe 4 52 6 Instrument Related Data Products 53 6 1 Time Series Data TSD Overview and structure 53 Gl Overview a ici rr A A ep ee A a ee 53 6 1 2 Physical file format of TSD o e 53 6 1 3 Nomenclature of Data Type o e e 54 6 1 4 Lime stamp ajo se be ee a A pa la 54 OD ESTATUS Da A th tok ea st A AI Are a A 55 6 1 6 TSD detailed description e 55 6 2 Calibration Constant Files CCF aoaaa a A 73 612 1 COR Structures 2d ai e a doa eee o Gk ee ek Ra ea he ans 73 022 Astor CRS oil es See ta ee He a ia ry a aa Pell Blan ih AE 76 AKARI FIS Data Users Manual lv A FIS Slow Scan Toolkit Cookbook 77 Azl Installation a ee ee hk ek Bee ce a 77 A LA Prerequisites cor sosa arca Pe ee eee ae Rad eee eS 77 A 1 2 Distribution package o 77 A 1 3 Setting and Starting up fisdr under Unix environment 78 A 1 4 Setting and Starting up fisdr under the Windows environment 80 A2 The Sl
84. nt phase correction e Difference between the internal source and the external source Absolute flux calibration Chapter 5 Caveats in the Data Processing The reduction software and calibration for the FIS Slow Scan observation is still at a rather preliminary stage As the analysis is progressing new complicated problems of the data will inevitably become apparent We try to describe the current limitation of the calibration to avoid user over interpretation of the data Up to date information about the calibration and data reduction will be included in this document and displayed on the observer support web page You are also welcome to contact the Helpdesk for any queries regarding the data reduction 5 1 Treatment for transient effects At present there is no formal treatment of transients in the Slow Scan data reduction tool Only after effects induced by calibration light pulses are considered and this only affects observations taken during the PV phase as the periodic pulse flashes were stopped for pointed observations in Phase 1 see Section 2 1 2 5 2 Straylight correction For point sources the stray light caused by the Earth shine reflected at the telescope baffle can be removed by the median filtering used for the background subtraction However diffuse sources with a size comparable to the median filter width are also filtered out by this median filtering The modelling and correction by stray light is still being analysed
85. ntitative evaluation is yet to be made The internal calibration sequence calibration lamps and shutter operation for pointed observations are described in the AOTs Astronomical Observation Templates 8 AKARI FIS Data Users Manual 2 1 3 Detector System Arrays The FIS has two kinds of detector arrays a set of two monolithic Ge Ga arrays for the SW channel 50 110 um and a stressed Ge Ga array for the LW channel 110 180 ym They are operated at 2 0 K Both the SW and LW channels consist of two photometric bands i e the FIS will have four bands in total which are operated simultaneously in scan mode In the spectroscopy mode only WIDE S and WIDE L are operated Figure 2 1 3 shows the FIS detector arrays in detail on the Focal Plane The upper detectors with three rows are the WIDE S and WIDE L bands and the lower ones with two rows are the N60 and N160 bands The FIS detector arrays are tilted with respect to the scan direction by 26 5 deg such that the interval between the neighbouring scan paths of the detector pixels is one half of the physical pitch of the pixels As noted above the SW and the LW detector arrays observe almost the same area on the sky The slight difference in the sky coverage is due to the difference of the projected array size Scan direction 8 arcmin Long Wavelength Pixel 44 2 x 44 2 Short Wavelength Pixel 26 8 x 26 8 FIS Pixel Format details Figure 2 1 3 Focal Plane
86. of the 5 sec case This ratio will be used for the flux calibration of point sources 3 2 7 Spectral Responsivity The relative spectral responsivity of the FIS system is presented in Figure 3 2 17 The responses are normalized at their central wavelengths The filter transmittance as well as the efficiency of the optical elements and the detector spectral responsivity are taken into account The filters and optics were measured in the end to end system configuration at room temperature The narrow band filters for N60 and N160 were measured individually at the cryogenic temperature since it was known that these filters showed a temperature dependent variation Relative Response Wavelength wm Figure 3 2 17 The spectral response curves of the four FIS photometric bands normalized at the central wavelength of each band These profiles should be regarded as typical for the bands 32 AKARI FIS Data Users Manual The detector spectral responsivity was evaluated using the FTS of the FIS itself with a blackbody source at different temperatures Each pixel of the detector shows a different spectral response This difference is larger in the LW detector which is stressed Ge Ga type The difference arises from the non uniform effective stress on the detector tips The stronger the stress pressure on the detector element the longer the wavelength limit can be extended It is observed that the cut off wavelength the longest wavelength at
87. of the pipeline program DATASTAT G00D Data status Describes data status mainly from completeness of telemetry data This does not tell detailed scientific quality of the data All appropriate error status are listed otherwise GOOD is given GOOD No problem INCOMPLETE Scientific data incomplete due to telemetry loss etc NOHK HK Status not available NOADS Attitude information not available STTINI STT did not work properly More status may be added as analysis progresses Data other than GOOD may not be in the archive at the first stage 58 AKARI FIS Data Users Manual Instrument information ORIGIN ISAS JAXA Organization creating FITS file Fixed TELESCOP AKARI 2 AKARI mission Satellite Name Fixed INSTRUME FIS 2 Identifier of the instrument One of FIS IRC FSTS G ADS DETECTOR SW Detector name Detector name One of SW LW Observation details following information is taken from Observation Database OBSERVER PI Name PI Name Observer s ID PROPOSAL PRPID 4 Proposal ID information about observation programme e g LSNEP LSLMC AGBGA OBS CAT MP 4 Observation Category Observation category One of LS MP OT DT CAL ENG PNTNG ID 1234567 Pointing ID Identification of the pointing observation Usually it is identical with the Target
88. om the PV observations of zodiacal light and cirrus emission The usage of LOCAL_FLAT may provide better flat fielding results for flat quiet skies T_FLA T_FLA T_START t_flat_start T_END t_flat_end They are only valid with the LOCAL_FLAT option and specify the data range used for local flat fielding They are in seconds from the beginning of the TSD data The defaults are T_FLAT_START T_FLAT_END PV data 540 sec 750 sec Phase 1 amp 2 540 sec 630 sec PLOT_ PIXEL plot_pixel gt ss_init_proc procedure displays several plots of data as a function of time index during the process This option specifies the detector pixel number s to be plotted The default setting is plot_pix 5 RAMP _COR_OFF Version 1 3 September 14 2007 85 Ramp curve correction non linearity correction is not applied before the linear fitting process Usually ramp curve correction is needed for all data sets GLITCH_RMV_OFF Do not detect mask glitches Options for calibration and map making The following options are passed to ss_make_map pro PIX_MAPPING By default ss_make_map pro creates so called foot print map each data point in the input time series data is placed on an image pixel closest to the data position With this option convolution by a disk of a radius corresponds to the beamsize is applied This fills void pixels often seen in some data TRANS_COR A simple correction of
89. oot C Documents and Settings astrof ASTRO F reduction gt for example fisdr_root C Documents and Settings myhomedir ASTRO F reduction Start win_fisdr vbs Click the icon of win_fisdr vbs If the set up is correct and IDL is properly installed in the system you will see that IDL starts and says FISDR Environment setup done In case of trouble check the above setup or contact to Helpdesk Version 1 3 September 14 2007 81 A 2 The Slow Scan tool The Slow Scan data reduction tools consist of a series of IDL procedures which are under the directory reduction slowscan In principle all processes can be controlled from the main routine ss_run_ss pro The processing of the FIS Slow Scan data consists basically of two steps which are executed by ss_run_ss making use of two main routines e ss_init_proc pro Flagging bad data measurement of sky signal and production of dark and responsivity correction tables e ss_make_map pro Calibration flat fielding and construction of co added images The following people mainly contribute to the development of the Slow Scan tool S Mat suura M Shirahata S Makiuti Yamamura T Suzuki ISAS A 2 1 Running ss_run_ss First Look Processing Consider an example set of pointed observation data in the directory ASTRO F fisdata AKARI_FIS_1234567_001 cd ASTRO F fisdata 1s AKARI_FIS_1234567_001 FIS_LW_20061225081641_1770 fits gz FIS_SW_20061225081641_1770 f
90. ow Scan tool ici eee ee ace ee oP aol Sec ee 81 A21 Running SS runes ates etn a a Pn be a oe a E 81 A 2 2 Available options for ss_run_ss 2 2 0 00 2 ee eee 83 A 2 3 Tips and suggestions for Slow Scan data reduction 88 As A Behind ss run8S jo 50 akg ee a ee ee Pe ce EE A A a 89 AS The FIS Data Visualizer FISv wee a Se ee AS 93 A 3 1 Main Functions Input Output a 93 A 3 2 Main Functions Display 0 0 0 a 97 A 3 3 Main functions Processing 2 20 ee 99 AA Contribution tools oe osea ap a p e a a as a Ee Ta a 100 A 4 1 Making mosaic images from multiple observations 100 Chapter 1 Introduction 1 1 Purpose of this document This manual is intended to give the FIS observer all necessary information to produce their data products The FIS IDUM should make the observer familiar with the FIS instrument its operations the output data the calibration and the processing To achieve this the following subjects are addressed e The FIS instrument and its operations e Some characteristics of the instrument that have implications for the data e An overview of the data processing e The calibration of the data and the accuracy A guide to the data products e How to start with the data e A cookbook for the usage of the processing tools Since this manual is intended to give the observer up to date information on the processing and the calibration of the FIS ins
91. port team welcomes the users participation FIS_ SW LW _20061225081641_1770_pr sav Time series calibrated detector signal and related information tt pr denotes Pre Reduction FIS_ SW LWwW _20061225081641_1770_cal sav Information of calibration lamp signal strength FIS_ SW LW __20061225081641_1770_dark sav Information of dark measurement signal strength FIS_ SW LW __20061225081641_1770_flat sav Information of flat fielding measurements FIS_ SW LW _ _pr sav contains the following information The data are time sequential 3542 data points of the SW 100 pixels detector _cal sav _dark sav and _flat sav files are also explained FISDR gt restore FIS_SW_20070705213613_1770_pr sav FISDR gt help RCOUNT LONG 3542 Number of data points number of ramps used 90 AKARI FIS Data Users Manual X_AVE DOUBLE Array 3542 Data sampling index averaged over each ramp COEFF DOUBLE Array 100 3542 2 Results of the linear line fit of each ramp pixels ramps coeff x 0 offset 1 tilt ERROR DOUBLE Array 100 3542 2 Uncertainty of the linear fit EG_GL_CNT INT Array 100 3542 Number of glitches detected in each ramp CAL_FLG_TOT INT Array 3542 Number of data points with calibration lamp is ON in each ramp If not zero the ramp contains calibration lamp signal SHT_FLG_TOT INT Array 3542 Number of data points with shutter open number of data po
92. pt in the case of a few pixels that require further investigation in addition the ramp curve correction for observations in extremely dark or bright sky conditions can be further improved Figure 3 2 13 Comparison of integration ramps under constant irradiation levels The LW detector right shows an almost linear response while the SW signal left deviates from linearity as the integration progresses 3 2 5 Saturation After Effect It is found that the saturation of the detector is followed by a decrease in the signal level Figure 3 2 14 This effect is more obvious in the LW channel The effect appears more significantly when the saturation is heavier It seems that the effect is already present when the integrated signal has reached about half of the full saturation level The recovery time scale is of the order of a minute This effect is still under quantitative analysis and is not yet implemented in the data reduction software 3 2 6 Transient response It is known that the Ge Ga type detectors show a strong transient response the detector output signal does not respond instantaneously to a change of incoming flux but rather has a delay of a few hundreds seconds time scale Figure 3 2 15 demonstrates how the transient response of the FIS detectors changes with a step change of incoming flux In order to simulate the real flight conditions a calibration lamp is turned on weakly to provide a background level for the SW detector
93. ptember 14 2007 89 A 2 4 Behind ss_run_ss In the following section we describe the two major steps in the Slow Scan processing They correspond to two separate programs ss_init_proc and ss_make_map These programs are ex ecuted from ss_run_ss Note that the contents of the following sections are subject to continuous update without notification Dark and responsivity correction tables ss_init_proc pro ss_init_proc generates dark and responsivity correction tables in V s which are used by ss_make_map for further calibration and map making This routine is called from the main program ss_run_ss with all available options Therefore users are not required to apply this routine directly ss_init_proc procedure makes use of the following routines ss_flux_ave pro calculates mean flux of line_fit data in a given time range ss_aftcal_ave pro makes a template of CAL after effect signal and output data table only for PV phase observations ss_q_to_radec calculates equatorial coordinates of each pixel from quaternion in GADS or AOCU data ss_init_proc produces several intermediate data files in the IDL save file format These files will be used at the following steps in the processing Users can ignore these files but those interested in the details and who would like to participate in the data reduction activity to improve the results are advised to contact the data reduction team in Japan via the Helpdesk The AKARI data reduction sup
94. r in the survey mode byte dacbiaswides DAC BIAS Wide S level 0x10 8 byte dacbiasn60 DAC BIAS N60 level 0x11 8 byte dacbiaswidel DAC BIAS Wide L level 0x12 8 byte dacbiasni70 DAC BIAS N160 level 0x13 8 byte daccalas DAC CAL AS level 0x14 8 byte daccalal DAC CAL AL level 0x15 8 byte daccalb DAC CAL B level 0x16 8 byte dacsinas DAC CAL sin conv AS level 0x17 8 byte dacsinal DAC CAL sin conv AL level 0x18 8 short tpbody FIS body temperature Ox3E 3F short tpsw SW Detector temperature 0x40 41 short tplw LW Detector temperature 0x42 43 short tpcalft CAL FT temperature 0x44 45 The rstcntn170 and dacbiasn170 should be renamed to rstcntn160 and dacbiasn160 respectively For historical reasons we keep the original name of the narrow LW band N160 as rstcntni70 and dacbiasn170 in the data structure 4 Detector data Either SW NDET 100 or LW NDET 75 data are included in one data set long det NDET Detector signal ADU float flux NDET Detector data in physical unit float ferr NDET Flux uncertaintity 5 Flags Flags are those set in the reduction software These flags are set for each frame sampling bit flag 8 Flag for detector condition 1 bad_frame set at all the unrecoverable frames Version 1 3 September 14 2007 aN 6 untrusted_frame 7 undef_anom_frame blank in_saa near_moon 8 reserved 63 de
95. r lines drawn in the JPEG image map Batch mode process control These options are prepared for batch processing at ISAS and are not relevant for the users NO_DISPLAY Running in batch process mode and do not display any plots on the screen MK_TXT_FILE Create text file format intermediate files This option remains for compatibility with the older versions It is not recommended for the observers 88 AKARI FIS Data Users Manual DEL_FILES Delete output files txt sav fits other than image jpeg files VERSION_COPY Copy the version file into the processed directory A 2 3 Tips and suggestions for Slow Scan data reduction Here we note some useful recipes for the Slow Scan tools for several typical cases we have experienced The Slow Scan toolkit has been used with a relatively limited number of data sets by the developers Comments and contributions from the users are welcome and will improve future versions of the pipeline AOCU option As of September 2007 the default positional information from G ADS is yet to be confirmed to be reliable Therefore we recommend to use this option to apply AOCU position and compare the results Improving flat fielding It is reported that the LOCAL_FLAT option often improves the flat fielding of the image It is most effective if the background sky is relatively smooth MEDIAN_FILTER is another option to correct any remaining offset between the scans pixels Very da
96. r sampling rate than in the photometric mode in order to properly sample the interferogram The narrow band detectors N60 and N160 are not used Table 2 1 2 Specifications of the FIS Fourier Transform Spectrometer FTS mode Wavelength wm 60 110 WIDE S 110 180 WIDE L m Full Resolution The actual position of the fields of view FOV of the detectors for the FTS mode are offset from one another compared to the originally designed position and is shown in Figure 2 1 6 Initial WIDE S Da eens 53 4 6 1 30 Scan Base E DO Base Current WIDE S post flight FIS03_P3 0 Moderate mode Initial WIDE L pre flight 6 6 FIS03_P3 1 Scan Base SW mode 102 62 105 Current WIDE L post flight Az a FIS03_P3 2 Scan Direction LW mode Figure 2 1 6 Actual schematic view of the FOV of the FIS detectors in FTS mode 12 AKARI FIS Data Users Manual 2 1 5 Instrument Operation The data acquisition process of the FIS is programmed into the hardware sequencer When the instrument begins an observation a preset specified sequence pattern is repeatedly carried out and the data are edited into telemetry packets and sent to the satellite s main computer Data Handling Unit DHU The data sampling timing is as accurate as the FIS internal clock and is quite stable The FIS data acquisition is continuous and reset of detector charge and calibration lamps and the shutter are controlled by the
97. re explio 8 7 20 stray_light Surface brightness MJy sr py CO AA ad fitting result lyy 4 16 0 04 MJy sr Lay tight 0 72 0 03 MJy sr 1104 1 5 104 210 2 5 104 310 3 5 10 Time of samples Figure 3 1 8 Time profile of a WIDE S detector signal during a Slow Scan observation over about 15 minutes the stray light component is seen as a global variation of the background level Brightness scale is based on an old calibration and may not be accurate Version 1 3 September 14 2007 27 3 2 Detector and instrument responsivity 3 2 1 Dead pixels The SW and LW arrays are known to have 4 and 7 dead pixels respectively In addition one SW pixel has a large noise level and an unstable signal output Figure 3 2 9 shows the positions of the dead and more badly performing pixels In addition one SW pixel 98 is very noisy and one LW pixel 42 shows strong non linearity in the integration ramps They are masked by the data reduction toolkit and not used in the data reduction a Lor COLEOL E O LA Ry WIDE L E Bog Eee ofe y ISLA Qe ly STA Sym Noo Lo el nN 2 Ze 7 SC N160 Figure 3 2 9 The positions of dead blue cross and badly performing green cross pixels in the FIS detector arrays Definitions of the pixel numbering indices are also presented 3 2 2 Responsivity and Uniformity Figure 3 2 10 shows the in flight and pre flight responsivities of all the SW detector pixels The values
98. recommended to put this directory under the default location your_home_directory ASTRO F cd mkdir ASTRO F cd ASTRO F tar xzvf fisdr_YYYYMMDD tar gz or gunzip c fisdr_YYYYMMDD tar gz tar xvf Change the directory name The system assumes that the files are under the ASTRO F reduction directory You may want to do one of the following under ASTRO F e Make a symbolic link We recommend this method ln s reduction_YYYYMMDD reduction e Change the directory name mv reduction_YYYYMMDD reduction Start up fisdr ASTRO F reduction startup bin fisdr This will startup IDL and set up several internal variables constants used in the system You may want to add the above path to your default setup or define an alias to the command in your cshrc or bashrc etc set path ASTRO F reduction startup bin path alias fisdr ASTRO F reduction startup bin fisdr If you prefer idlde environment you can call it with the de option fisdr de Environment variables Two environment variables are defined for stating up the Slow Scan tool FISDR_ROOT specifies the fisdr ROOT directory where all the package files are stored The de fault the value applied when this environment variable is not set is ASTRO F reduction Version 1 3 September 14 2007 79 setenv FISDR_ROOT my reduction directory reduction for csh tsch etc and FISDR_ROOT my reduction directory reduction export FIS
99. rect in this case Determination of the position of the center burst Since the value of the position sensor is correct only relatively the center of the optical path must be determined In fact the center depends on the wave number so a wavenumber dependent phase correction is needed However the present toolkit determines the position of the center that minimizes the imaginary part integrated over the effective wavenumber The determination is a two step process First the deviation of the center position between different scans is estimated For this purpose the most sensitive pixel SW pixel 23 and LW pixel 31 see Fig 3 5 20 is used or alternatively a pixel detecting a point source It is then assumed that the relative deviation of the center position between different scans is the same for all pixels Next the deviation of the center position between different pixels is estimated Interpolation of bad data We replace any bad data by the median of other scans Since the first scan in the SED mode is affected by an irregular drive pattern at the starting point we ignore the first scan when calculating the median in the SED mode Fourier Transform After applying Fourier transforms to the interferogram of each and every scan a correction for the slight variation of the responsivity within one pointed observation is made by scaling with the integration of the effective wavenumber 85 160 cm for SW and 65 85 cm for LW except
100. rget However we have not detected any significant difference between the PSF measured from the observations of asteroids and luminous infrared galaxies The evaluation is continuing TE 4 1 gt N60 Model D 0 8 L Gaussian Y 0 8 Data 5 g 2 0 6 0 6 3 E N04 N04 5 0 2 5 0 2 zZ Z 0 0 180 120 60 0 60 120 180 180 120 60 0 60 120 180 Distance arcsec Distance arcsec Figure 3 1 1 Comparison of the measured and modeled PSF for the SW detector 21 22 AKARI FIS Data Users Manual 1t 4 1 Wide L Model Pa 3 0 8 L Gaussian Y 0 8 5 Data 5 0 6 0 6 3 E A 0 4 N 0 4 3 5 0 2 6 0 2 2 Z Ok O ta 180 120 60 0 60 120 180 180 120 60 0 60 120 180 Distance arcsec Distance arcsec Figure 3 1 2 Comparison of the measured and modeled PSF for the LW detectors There are large deviation in the skirt part of the measured PSF from the model The reason for this deviation has not yet been well understood 3 1 2 Cross talk and ghosts Cross talk between the detector pixels will broaden the effective FWHM of a point source image Moreover it will increase the effective number of glitches and complicate the transient response This effect is more serious in the SW detector since it is a monolithic structure Figure 3 1 3 Cross talk and ghost effects as seen in a FISO1 observation of
101. ring CRTRVER PIPELINE DATASTAT ORIGIN TELESCOP INSTRUME DETECTOR OBSERVER PROPOSAL OBS CAT PNTNG ID TARGETID SUBID OBJECT OBJ RA OBJ DEC AOT AOTPARAM INSTMODE TIMESYS DATE OBS DATE END DATE REF AFTM OBS AFTM END AFTM REF PIMTIOBS PIMTIEND PIMTIREF EQUINOX RA DEC ROLL AA SOL AA EAR AA LUN TM SAA SAT POSX SAT POSY SAT POSZ DAYNIGHT STTA NUM STTB NUM STTA MOD STTB MOD HISTORY Lo vs ve ve ve ve ve ee vs vs ve vs vs ve we we we we AKARI FIS Data Users Manual Version of CREATOR Data Processing Pipeline name Data status Organization creating FITS file AKARI mission Identifier of the instrument Detector name PI Name Observer s ID Proposal ID Observation Category Pointing ID Target ID Sub ID Object name degree Target position degree Target position Observation AOT AOT Parameter Instrument operation mode Explicit time scale specification Observation start date time Observation end date time Reference time in the Observation DATE OBS in ASTRO F Time DATE END in ASTRO F Time DATE REF in ASTRO F Time DATE OBS in PIM TI 36bits DHUTI DATE END in PIM TI 36bits DHUTI DATE REF in PIM TI 36bits DHUTI Epoch of Coordinate degree Target position at DATE REF degree Target position at DATE REF degree Roll Angle at DATE REF degree Solar avoidance angle at DATE REF degree Earth avoidance angle at DATE REF degree Lunar avoidance angle at DATE REF se
102. ring option MEDIAN_FILTER in the time domain with a default window size of 10 data points 10 ramps The stray light is also removed by this DC rejection filter see Figure 4 2 7 However diffuse sources with a size comparable to the median filter width will be also filtered out by this procedure For this case a different routine to model and subtract the stray light SL_RMV is under construction see Figure 4 2 8 In the model the baffle function is assumed to follow an exponential law I B A x exp 9 C where J is the signal B is the sky background A is a fitting constant O is the Earth avoidance angle and C is a scale angle 0 4 rad In addition the option SKY_SUB is also provided in the Slow scan toolkit to subtract the mean sky level determined from the data before the Slow Scan during the stabilization 44 AKARI FIS Data Users Manual Median filterin A A Nha recorta LHEX2_sw_subset_fit dat u 1 211 LHEX2_sw_subset_fit_median dat u 1 211 fittin 15 g la gt 10 2 Point source E gt a f D 5000 10000 15000 20000 25000 Time index Figure 4 2 7 Background subtraction for point sources and small scale structures T T T T Before subtraction S After subtraction Brightness MJy sr L L o 5000 10000 15000 20000 25000 Time index Figure 4 2 8 Baseline fitting with a stray light model 4 2 6 Making images by co adding multi pix
103. ritten in IDL To begin the FISv tool you simply start a fisdr session as explained at the beginning of this chapter and type fisv or FISV Then you will see a window similar to that shown in Figure A 3 1 A 3 1 Main Functions Input Output There are four action buttons to open and save TSD files and to close the FISv application When a TSD file is opened all the different options and functions become active as shown in Figure A 3 1 The option Open TSD file from LDS is not applicable to the users as it is for accessing the Local Data Server at ISAS Japan 94 AKARI FIS Data Users Manual lv FIS Data Visualizer File Main Tools Pipeline Help Ea al al home2 everdugo FIS_data_reduction data FIS20060802053000_1800_lw fits gz Y axis Ey FIS_OBS E G Time D Status 3 AFTIME Analg Telemetry E PINTIORG Ey letector Data FISTIORG i SOE PINTI Dj FLUX i E FISTI _ FERR Header View Plot All E Status Flags a fnalg Telemetry B G uality Image of det Masked Plot Le L B Detector Data E Counter o Flags FISH TSD Editor eG Quality y IRC_HK eee antics 4 a 1HK_2 4 GB Batch GB FlagBad Plot Table Print Ps GB Cnyay BLAA L Good day everybody c ISAS JAXA AKARI FIS Data Visualizer Ver 3 13 for TSD4 fhome2 everdugo F1S_data_reduct ion data F1520060802053000_1800_luw fits gz has been op
104. rk sky Give T_FLAT_START and T_FLAT_END to cover the entire observing region together with LOCAL_FLAT If the sources in the region give only minor contribution to the total flux from the region this could even further improve the flat fielding The data range in seconds from the beginning of the file can be obtained with FISv See Section A 3 by selecting aftime in X axis Measuring the sky brightness If absolute sky brightness of the diffuse radiation is important try SL_RMV and TRANS options together Point sources Small extended sources Try SL_RMV TRANS MEDIAN or TRANS MEDIAN FILTER Applying MEDIAN_FILTER option improves the RMS noise of the image and is useful to detect faint point sources MEDIAN_FILTER and SMOOTH_FILTER For the bright sources SMOOTH_FILTER results in smaller holes next to the sources SIGMA option Try SIGMA 1 5 which may remove more outlier data points resulting in better images Comparison between scans in an observation SCUT option will produce separate images for each one way scan in the observations You can compare them for cross checking of detections and consistency of the positions etc Removing glitch effects Tf bright lines stripes are observed try using a BAD_THRSHLD lower than the default 10 Often such stripes are responsivity jumps due to glitches By giving a lower BAD_THRSHLD pixels with a responsivity level higher than nominal can be discarded Version 1 3 Se
105. rmation The following example data are time sequential 879 data points of the SW 100 pixels detector IDL gt restore FIS_ SW LW _ _ar sav IDL gt help RA DOUBLE Array 100 879 DEC DOUBLE Array 100 879 Position information of every pixels at every sampling points Version 1 3 September 14 2007 93 DET DOUBLE Array 100 879 Calibrated detector signal ERR DOUBLE Array 100 879 Uncertainty of the detector signal EG_GL_CNT INT Array 100 879 Number of glitches detected in each ramp BAD_FLG INT Array 100 1 for band pixels not used in the processing X DOUBLE Array 879 Data sampling index averaged over each ramp AOT STRING P12_FISO1 DATA_TYPE STRING FIS_SW Information about the observation N_INT INT 1 Value given by N_RAMP_DIV option 1 default data point corresponds to each ramp RST STRING 210N RST_INT DOUBLE 0 94936709 The actual reset interval in seconds AOCU_ADS INT 1 GLITCH_RMV_OFF INT 0 RAMP_COR_OFF INT 0 Options for ss_init_proc pro 1 ON A 3 The FIS Data Visualizer FISv The FIS Data Visualizer FISv is a Graphical User Interface GUI tool that has been created in order to provide a method of easy access to the FIS data Time Series Data TSD and to easily display time series data such as the detector signal Instrument status flags etc FISv is distributed as part of the Slow Scan toolkit and is w
106. rofiles of the detector signals from wide and narrow band detectors These plots clearly demonstrate that the ghost signal appears in one detector when the other detector observes a bright object Output Siganl V s Calibration Calibration Sequence Sequence ae gees T 7 f r y a 0 012 SW peo Chamnel 49 Wide S aerae dd Channel 69 N60 N60 0 008 E l Pa i F IN i E HA pa 0 004 L PA HA y H ji ae SD J j a el 0 000 Ghost Ghos 4 E Wide S N60 E 1 1 1 I 1 1 1 1 600 700 800 900 1000 Time s Figure 3 1 4 Time profile of signals from two SW detector pixels during one round trip scan of a Slow Scan observation of a very bright source The target passes from N60 to WIDE S then back again after the calibration sequence in the middle of the operation A ghost signal is observed when the other detector was looking at the target Output Siganl V s 0 030 0 025 0 020 E 0 015 A MOT 0 010 E 600 Cal ibration Calibration LW ON Source ENt60 ON Source Wide L Sequence m r Sequence a Channel Channel 38 Wide L 53 N160 A a danada Jl AGA er i 800 Time s 1000 Figure 3 1 5 Same as Figure 3 1 4 but for the LW detectors Only the ghost in the N160 is shown Ghos
107. s The shape without optical distortion is also plotted for comparison blue This distortion data is provided as part of the data reduction pipeline package The distortion will be further evaluated with the in flight data and the information will be correspondingly updated in the future FIS SW Distortion Pattern 2005 June FIS LW Distortion Pattern 2005 June T T T T T CORNER F sl 25H Y k T 20 LNOCAn arcuun AHOAN ATC hu un T CrossScan arcmin CrossScan arcmin Figure 3 1 6 The FIS detectors projected onto the sky with red and without blue optical distortion Version 1 3 September 14 2007 25 3 1 5 Polarization The dichroic beam splitter used in the FIS is known to have polarization In Figure 3 1 7 the transmittance and reflectivity of the filter is given The reflection was measured at two different angles perpendicular to each other A difference in performance at a few specific wavelengths at approximately 160 and 180 cm corresponding to 63 and 55 um respectively was observed Unfortunately the angle of the filter in the flight module instruments is not accurately known and this difference will result in an uncertainty in the measurement of the polarized light Optical performance of Dichroic Filiter non FM 90cm edge 30deg transmission 90cm edge 30deg reflection 90cm E 30deg reflection pol retated 90deg 08 0 6 0 4 Transmission
108. s the LW sensitivities are degraded by a factor of 8 2 x 4 in 2 second integration and by a factor of 4 2 x 2 in the 0 5 second integration case 2 2 4 Saturation Limits for FISO1 amp FISO2 The saturation limits are functions of the reset interval only These limits are defined such that the integration ramps of the high sensitivity pixels reach a level where the reproductivity of the ramp shape becomes bad Beyond this level we still obtain data from the lower sensitivity pixels but photometric accuracy and quality of reconstructed image map may be significantly degraded The in flight measurements of the saturation limits are yet to be assessed although may be similar to those quoted in the Observer Manual Table 2 2 6 gives the Observers Manual saturation levels for these FIS AOTs Table 2 2 6 The saturation limits for FISO1 and FISO2 AOTs Note that at present these saturation numbers have not been confirmed in the flight configuration Point Source Jy 03 20 280 140 70 60 30 15 120 50 15 300 130 60 Diffuse Source GJy sr 4 0 2 0 1 0 50 Version 1 3 September 14 2007 19 2 2 5 FISO3 FTS Spectroscopy The FISO3 AOT is designed for spectroscopic observations with the FTS Table 2 2 7 FISO3 summary Fixed parameters Observing Mode Spectroscopy Band WIDE S WIDE L Scan pattern Staring no Step Scan User specified parameters Sampling mode Nominal fixed Reset interval 0 1 0 25
109. s Manual AOCU_ADS Use the AOCU determined boresight position instead of default G ADS position data Options for signal measurements The following options are passed to ss_init_proc pro N_RAM P_DIV n_ramp_div By default a linear fit is applied to each integration ramp to derive the signal level If N_RAMP_DIV greater than 1 is given A ramp is divided into n_ramp_div s and linear fitting is made for each segment of the divided ramp Taking n_ramp_div greater than 1 provides higher spatial resolution in the in scan direction at the cost of noise level as well as increased calibration uncertainty due to any remaining non linearity of the ramps after the correction USE_ BAD In addition to automatic detection and flagging of the bad data by the program this option force the program to refer to PIXEL_BAD flag in the input TSD and discard flagged data This option is used to reflect the results of manual flagging of data prior to use of the Slow Scan tool with the FISv data browser Default is that PIXEL_BAD is not checked LOCA L_FLAT To use the blank sky data in the observation for flat fielding If T_FLAT_START and T_FLAT_END as specified below are not provided the data during attitude settling approximately 420 630 sec from the beginning of the data are used for the correction Without this option flat fielding is applied using the nominal flat built fr
110. scribed by the other flags 1 unusable data but the anomaly cannot be described by the existing flags blank 1 in SAA 1 near moon 1 aa_lun is used for lunar avoidance angle in GADS extension incomplete restitution of higher order bits of DET These flags are set for each frame sampling and each pixel bit Lis 2 NO fF 00 9 10 11 12 13 14 15 16 pix_flag 32 NDET bad undef_anom arith_err dead saturate reset rstanom no_diff no_rp_corr no_dk_corr no_dccal_corr no_tr_corr no_flat_field no_gpgl no_mtgl no_abscal ti Flag for each pixel condition bad pixel 1 unusable data but the anomaly is not described by any other flags special values for undefined results NaN and INFINITY dead pixel 1 saturated pixel 1 data taken just after reset 1 anomaly seen in a few certain samplings just after reset No differentiation enable 1 impossible to carry out ramp curve correction dark has not been subtracted successfully DC responsivity correction has not been corrected successfully transient effect has not been corrected successfully flat fielding has not been carried out successfully unable to search correct for glitch unable to search correct for glitch abs flux calibration has not been done successfully For glitch detection using Gaussian Processing method Kester 17 18 19 20 21 gpgl_typel gpgl_type2 gpgl_type3 gpgl_type4 gpgl_tail
111. sion Results of pointing reconstruction is stored in this extension 1 Time double aftime ASTRO F AKARI Satellite Time calibrated which is the time since 2000 January 1 00 00 UTC longlong pimtiorg PIMTI counter from original packet 2 Status bit status 8 Satellite attitude status 1 blank blank 1 2 8 reserved Details will be discussed with ESA 3 Analog telemetry double quaternion 4 Quaternion at boresight double pos_err 3 Estimated error of position double body_rate 3 Body rate Angular velocity at boresight double ra J2000 R A deg at boresight double dec J2000 Dec deg at boresight double roll Roll angle at boresight deg double d_ra Scan rate in J2000 R A double d_dec Scan rate in J2000 Dec double d_roll Scan rate in roll angle double el_sol Solar elongation double aa_sol Solar Avoidance Angle double aa_ear Earth Avoidance Angle double aa_lun Lunar Avoidance Angle double crs_off Offset in cross scan direction from Nominal scan path 4 Quality bit quality 8 Quality Flag for condition 72 AKARI FIS Data Users Manual Satellite Ephemeris SE extension The following information is calculated from the satellite orbital parameters provided three times a week 1 Time double aftime longlong pimtiorg 2 Status bit status 8 blank type daynight in_saa in_polar 6 8 reserved oP WN 3 Analog value double tm_saa doub
112. t of two pipelines named fts_partl pro and fts_part2 pro The former reduces the Time Series Data TSD and provides raw spectra and the latter applies flux amp spectral calibrations and reduces the fringes The processes contained within these two pipelines are listed below raw data TSD 1 Flag bad data gb_flag_bad_data gb_set_flag_rstanom 2 Convert to voltage units gb_conv_to_volt Ramp curve correction gb_ramp curve_corr gt w Differentiate data gb_differentiation Interferogram DC component Separate into individual scans Remove reset anomaly and glitches Subtract DC component Interpolate bad data O OG N Q A Determine the position of the center burst 10 Discrete Fourier transform 11 Average the spectra Raw spectra end of fts_part1 12 Apply spectral correction factor and flux calibration 13 Remove fringes Spectra end of fts_part2 Version 1 3 September 14 2007 49 4 3 2 Brief description of each process Ramp curve correction The standard Green Box module is used to correct for any non linearity of the ramp curve see section 4 1 2 The correction table is made from the interferogram far from the center burst using observations of targets of various brightnesses N B For very bright targets whose brightness exceeds the range of the correction table you have to make a correction table from your data itself In the present toolkit the calibration will be incor
113. ted below These numbers are regarded as correction factor from the measured flux to the real flux of the sources Band Factor N60 1 7 WIDE S 1 7 WIDE L 1 9 N160 3 8 For the moment there is no clear explanation of the discrepancy between the expected flux and measured flux The uncertainty of the photometry using the above method is crudely estimated as 20 in SW and 30 in LW Especially the number for the N160 band needs special care to use as only three objects were available for the analysis Colour correction Based on internal report by Y Hibi 2006 Dec 25 The FIS photometric flux is defined for a flat spectrum vF const at the defined Central Wavelength Frequency of each band Table 2 1 1 Colour correction factor K is given by pa a E Ray 4 2 4 Version 1 3 September 14 2007 47 where Fyops is the flux of the object Fygat is the flux of the flat spectrum R v is the Relative Spectral Responsivity Function RSRF Figure 3 2 17 normalized at the Central Frequency Colour correction is applied as F real F obs K 4 2 5 Correction factors for typical cases are tabulated in Table 4 2 1 and 4 2 2 Table 4 2 1 Colour correction factor K for a spectrum F v x v Band N60 WIDE S WIDE L N160 4 1 08 0 97 1 23 1 06 2 1 01 0 96 1 05 1 01 a 0 1 00 1 08 0 96 0 99 2 1 05 1 41 0 94 0 99 1 17 2 20 0 97 1 01 Q Table 4 2 2 Colour correction f
114. tion System G ADS re calculates the attitude with a greater degree of care Both data are recorded in the observation data file Both systems use the same input data from the on board Attitude Control System sensors and there should only be minor differences in the absolute positional accuracy Nevertheless the G ADS is expected to provide more reliable information than the AOCU since this data includes fine tuning of the algorithm and software system to the input data The Slow Scan data reduction tool uses G ADS information by default However as of February 2007 the tuning of the G ADS system has not been completed and the results are not accurate enough under some conditions Such inaccuracies may appear in the reduced images as an unexpected elongation of the images It is recommended to run the software with the AOCU_ADS option and to compare the results with the default G ADS processing The G ADS is expected to be improved in around a months time Note that the Pointing Reconstruction processing is carried out with the data from the Focal Plane sensors for the All Sky Survey by ESAC ESA which will provide better than a few arcsec accuracy Positional error has been crudely evaluated using around 40 SW and 20 LW point like sources reduced by the Slow Scan tool in the standard manner The deviation of the centroid position on the image maps from the catalogued positions scatters with a lo dispersion of 6 and 11 arcsec in the in scan an
115. tively provided This shortest reset interval is available thanks to the 5 7 times faster detector sampling rate in this operation mode Target position New Due to the misalignment of the detectors see Section 2 1 3 and Fig ure 2 1 6 three different positions are defined Position 0 Target at the overlapping region of the two detectors pixel 7 for WIDE L and pixel 33 for WIDE S 3The actual reset interval is 0 14 sec 20 AKARI FIS Data Users Manual Position 1 Target is located on the 2nd column of the WIDE S detector array near pixel 28 29 Position 2 Target is at the center of the WIDE L array pixel LW 23 2 2 6 Performance of FISO3 The flight sensitivity of the FIS03 FTS mode is known to be worse than the pre flight values given in the Observers Manual Although a quantitative evaluation of the flight performance is given below users of FISO3 are still urged to contact the FTS team in Japan via Helpdesk The flight sensitivity of the FIS03 FTS mode has been estimated from the signal to noise ratio of bright sources for a portion of the observation modes and specific pixels Noise is defined as the dispersion between different scans in one pointed observation The sensitivity for the continuum emission is estimated from Neptune observed with the AOT position parameter 0 i e it is derived only for the SW33 and LWO7 pixels The 50 detection limit is roughly 20Jy for 65 85 cm LWO07 and 50Jy and 100Jy for 90 120 c
116. tivity for the All Sky Survey is expected to recover by a factor of a few with this bias light The SW detectors do not require such a mechanism 2 1 4 The Fourier Transform Spectrometer FTS The FIS provides the opportunity for imaging spectroscopy over its full wavelength range 60 180 um using the two wide band arrays WIDE S and WIDE L The Fourier transform spectrom eter of the FIS is of the Martin Puplett type Figure 2 1 4 This polarizing type Michelson interferometer uses input and output polarizers to create a linearly polarized beam and another polarizer to split the beams to a fixed and moving mirror to make the interferogram The in put and output polarizers are mounted on the filter wheel These polarizers reduce the optical efficiency of the instruments by 1 4 ideal case compared to the photometric mode The total optical efficiency is thus 10 20 The moving mirror driven by an electromagnet can shift 9 2 mm from its physical center The optical center zero path position is displaced by 4 6 mm from the physical center and the optical path length is asymmetric to the center Two preset operation modes are provided for observers Full resolution mode and SED mode Figure 2 1 5 They are in principle different only in the mirror scan path length and accord ingly in the resultant spectral resolution The Full resolution mode uses the full physical path AKARI FIS Data Users Manual Fixed Roof top Mirror y 4 Mo
117. trument it will be updated regularly Every change in the FIS data reduction software the calibration procedures or the file descriptions will be reflected in this manual 2 AKARI FIS Data Users Manual 1 2 Relevant information AKARI Observer s Web The ISAS Web page contains the most up to date information URL http www ir isas jaxa jp AKARI Observation The ESAC page also includes up to date information URL http akari esac esa int observers Helpdesk Any questions and comments on AKARI observations and user support are addressed to the AKARI Helpdesks iris_help ir isas jaxa jp http akari esac esa int esupport Version 1 3 September 14 2007 Chapter 2 Instrument and AOT Overview The Far Infrared Surveyor FIS Instrument is designed primarily to perform the All Sky Survey in four wavelength bands The instruments are operated such that data acquisition is contin uously made as the telescope scans the sky resulting in sets of strip data of sky brightness This operation can also be used for pointed observations in a Slow Scan mode The FIS is also equipped with a Fourier Transform Spectrometer FTS that enables imaging spectroscopy over the full FIS wavelength range FTS observations are only made as pointed observations Version 1 3 September 14 2007 5 2 1 Hardware Specification 2 1 1 Overview The specifications of the FIS instrument are summarized in Table 2 1 1 It provides four pho tometric bands b
118. ts in the WIDE L band appear in different detector pairs and are not shown in this plot The relative displacement of the ghost from the source object are approximately evaluated 24 AKARI FIS Data Users Manual and summarized in Table 3 1 1 The direction of the ghost is most easily understood when the NARROW and WIDE images are aligned in time domain such that the edges in the in scan direction of the two images are overlaid to each other The ghost appears where the source is observed in the other bands See Figure 3 1 3 Table 3 1 1 Relative displacement of the ghost from the source object The uncertainty of the values is about 0 2 arcmin Detector SW LW In scan arcmin 5 4 3 6 Cross scan arcmin 0 2 2 0 Distance arcmin 54 4 1 3 1 3 Leakage A combination of two blocking filters at the entrance aperture are expected to reduce the short wavelength light leakage to factors of 1075 at 10 um and 107 at 0 5 um optimally However no end to end measurement has been made and the leakage could be as worse as 107 107 at 0 5 um Note that we have not detected any signature of blue light leakage from the blocking filter so far 3 1 4 Distortion Figure 3 1 6 shows the detector shape projected onto the sky Due to the fact that the FIS aperture entrance is about 20 arcmin away from the center of the focal plane boresight and that the FIS optics are an off axis design significant distortion of the detector shape is observed red line
119. und trip scan is mandatory to ensure data redundancy The cross scan shift is used to increase the redundancy or to observe a wider area of the sky The scan speed is either 8 or 15 arcsec sec These speeds are selected to maximize the performance sensitivity while enabling observations of a certain size area of sky User specified parameters The following inputs are given by the observer Detector readout mode Nominal CDS CDS mode should only be used for the bright est targets that would normally saturate the detector in Nominal mode See Section 2 1 3 for the details of the readout methods Reset interval This parameter is only relevant for the Nominal readout mode and is chosen based on the brightness of the targets Generally a longer reset interval improves sensi tivity in the amplifier but at the same time increases the risk of saturation On the other hand a shorter reset looses more data points at the resets 14 Manual Step_scan Scan_p15 Pre cal sequence Shut_cls Shut_opn aE 975 1005 Post cal sequence Settling time Step 30s f Shut_opn 420 3 _p15 Shut_cls 1351 630 A gt A gt Calon Cal off 990 997 6 Scan area length 0 66 deg for 15 s or On target On target 0 35 deg for 8 s 708 75 896 25 083 75 1271 25 area center or source Each scan 157 5s Each scan 157 5s v Shut_cls zrs W 817 5 snu W LJ Shut_opn 1192 5 Shut_opn 1162 5 Us Cal_off 810 1 2X Cal_off 1185 1
120. us sources therefore careful consideration must be given to the treatment of confusion noise and the confusion limit as in reality the confusion noise is a convolution of the observational phenomenon and the observing instrument At present there are no in flight measurements for the confusion noise for AKARI observa tions therefore users are directed to the pre launch estimates of confusion for the mission 3 4 1 Confusion Due to Diffuse Background Emission The galactic cirrus is a function of galactic latitude and is serious for wavelengths longer than 60 um The formalisation of Helou amp Beichman 1990 can be used to provide an estimate of the confusion noise mJy due to infrared Cirrus as a function of Cirrus brightness lt B gt for the AKARI telescope ao 0 732 ImJy Com D 0 7m 2 5 Mayer yee 3 4 1 Table 3 4 2 shows the estimated confusion limit over a range of average Cirrus brightnesses lt B gt 3 4 2 Confusion Due to Point sources The point source galaxy confusion limit is defined as the threshold of the fluctuations in the background sky brightness below which sources cannot be discretely detected in the telescope beam A D Point source confusion will affect AKARI observations in the faint flux regime and in crowded fields As a benchmark for observations a useful practical benchmark for the confusion limit is adopted by assuming a limiting the number sources per bea
121. vable Roof top Mirror 10 Collimeter Mirror Long Wavelength ey Detector WIDE L 7 Bending Mirror Short Wavelength Detector WIDE Bending Mirror Camera Mirror Figure 2 1 4 The optical diagram of the FIS Fourier Transform Spectrometer FTS length while the SED mode scans 4 6 mm with respect to the optical center The mirror moving speed is always a constant 0 367 mm sec for SED mode and 0 382 mm sec for Full Resolution mode Taking an interferogram scanning one way takes 48 sec in Full Resolution mode and 12 sec in SED mode Full Resolution mode Av 1 2 76cm 0 36 em 9 2mm Omm Optical PL Mechanical PL 27 6mm Drive Speed 0 367 mm sec SED mode Av 1 0 425 cm 2 4 cm 48 sec 96 sec Drive Speed 0 382 mm sec Optical PL Mechanical PL Figure 2 1 5 The mirror driving patterns of the FIS FTS There are two modes Full Resolution mode and SED mode The spectral resolution defined as 1 L L is the optical path length is about 0 36 cm for the Full Resolution mode and 2 4 cm for the SED mode respectively Note that these values Version 1 3 September 14 2007 11 assume apodization at the spectrum reconstruction Better spectral resolution may be obtained by optimizing the data reduction procedure The specification of the FTS mode is summarized in Table 2 1 2 In FTS mode the WIDE S and WIDE L are operated simultaneously with a highe
122. ve the sky signal and is relatively robust to the high frequency noise SW ch001 Frequency He o ME 1730 1740 1750 1800 1810 1820 1830 Time 2200500 14173000 00E0 08 001 100 sw_0 999899989 06 txt Figure 3 2 12 Noise spectral profile of a SW detector pixel Time variation of the noise spectra taken during the laboratory test under dark conditions White stripes are excess noise compo nents We observe a number of components at specific frequencies Some of them move with time Version 1 3 September 14 2007 29 3 2 4 Ramp curve Ideally the output signal of the FIS detector should be proportional to the number of incoming photons but this is not the case in reality The actual ramp curves show deviations from the optimal linear line even when the data is taken under constant incoming radiation The SW detector shows this effect more prominently Figure 3 2 13 As the slope of the ramp curve gives the instantaneous flux any deviation from linearity means that the responsivity changes along a ramp Currently the SW ramp curve becomes flatter as an integration progresses The non linearity of the LW detector is 5 10 If the shape of the ramp curve is reproducible and if the curve is monotonic with incoming flux it will be possible to correct this effect Analysis of the flight data has shown that the ramp shape is relatively stable over a period of several months The ramp curve correction module works effectively exce
123. y time the session is reset by the reset_session command so that users can maintain the proper environment In the earlier version you may be able to recover the environment with IDL gt fisdr command though earlier versions are not officially supported 80 AKARI FIS Data Users Manual A 1 4 Setting and Starting up fisdr under the Windows environment The fisdr system should also work properly under the Windows environment although it is not thoroughly tested Contributions from users are welcome File extraction User should prepare file extraction tools for tar gz file The usage of such tools is dependent on the specific software so it is not explained here The file can be located anywhere in the PC but may be somewhere like ASTRO F reduction under the users home directory Change the directory name Similarly to the Unix system change the directory name from reduction_YYMMDD to reduction Creating a shortcut is also possible Setting the startup script We provide a Visual Basic Script for starting up the fisdr system on Windows You need to edit the script for your personal environments The script file is HOME ASTRO F reduction startup bin win_fisdr vbs You can copy the file to Desktop or anywhere you like Open the file with editor and set the fisdr_root variable to point the directory where you have the system Please edit the following line to point the directory where you locate the toolkit fisdr_r

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