POLDER Level-1 Product Data Format and User Manual
Contents
1. Appendix F POLDER radiometric model The POLDER CCD pixels are numbered 1 j as seen in Figure 1 For the polarized bands analysor 2 is parallel to axis j matrix smaller axis and analysors 1 and 3 are turned by about 60 from analysor 2 Analysor gua directions General direction of ADEOS motion POLDER Matrix IM Approximative crosstrack direction Figure 1 The matrix pixel i j images the incident radiance corresponding to zenith viewing angle 0 and azimuth viewing angle such that Ji 0 Arcila dej oF LP tel HEL d i ig where j correspond to the central pixel f is the instrument focal length and dq dc are the CCD pixel sizes a CCD pixel is not square Note that these angles are defined in the instrument reference frame not in the target Earth fixed frame Meridian plane po direction AX Matrix pixel Electric field direction Analysor a direction Figure 2 The incident light is assumed to be linearly polarized and its Stokes parameters Q U are defined with respect to axes 1 1 respectively parallel and perpendicular to the meridian plane For a perfect instrument the numerical count CN H corresponding to pixel i j in wavelength filter k k 1 2 9 and polarizer number a a 1 2 3 writes POLDER level 1 Standard Product User manual page 29 CN A 1 cos 2a Q sin 2a U 1 where A is the calibration coefficient and2. stands for the angle between the meridian plane and the analysor a directions The instrument is not perfect however and we write the radiometric model in a generalized form CN t Argh OyT BRL PSQ Pu CNP 2 where 0 e CN is the darkness current e t is the integration time ms p accounts for the low frequency variation of the optics transmission it is normalized to p B 0 1 ge is the matrix pixel equalization coefficient which takes into account high frequency variations in the optics transmission and in the CCD sensitivities For each filter gi a 1 for the central pixel i 121 jo 137 e T accounts for differences in the transmission of the 3 analysors of one given spectral band It is normalized according to T 1 for the central analysor In a first order correction of the lens and filters optical effects the coefficients PI PQ and PU can be writen as PF 1 9 e 9 cos 2a Ph n e 0 cos 2a EMsin 2ap 3 Pit sin 2ork E cos 2a 2a 2a 120 2a with 26 o E 0 4 2a 2a 120 2a8 E The physical interpretation of the correction terms used in eq 3 and 4 are given below n which is on the order of 1 accounts for the imperfect extinction of the polaroids It varies with wavelength and with the integration time because of the polarizer rotations during the acquisition e 0 lt lt 1 accounts for the linear polariza
3. POLDER level 1 Standard Product User manual page 2 Introduction The purpose of this document is to describe the POLDER level 1 data format and to provide some information on how the data were derived from the measurements The document first gives some information on the POLDER instrument its observation principle and the level 1 data processing It then describes in details the level 1 data format The appendices provide some tools and equations for an in depth use of the POLDER level 1 data The POLDER instrument on ADEOS The POLDER radiometer design consists of three principal components a CCD matrix detector a rotating wheel carrying the polarizers and spectral filters and a wide field of view FOV telecentric optics Deschamps et al 1994 The optics have a focal length of 3 57 mm opening to f 4 5 with a maximum FOV of 114 The CCD sensor array is composed of 242 x 274 independent sensitive areas The total array detection unit size is 6 5 x 8 8 mm which according to the lens focal ratio corresponds to along track and cross track FOVs of 43 and 51 respectively and to a diagonal FOV of 57 The CCD array is equipped with an antiblooming device which prevents image degradation when the incident radiance is above the sensor s dynamic range The spectral sensitivity of the CCD array extends between 400 and 1050 nm The rotating wheel which has a steady period of 4 9 s supports the interference filters and polariz
4. 765 865 thresholds are defined by the ocean color mission requirements 443P 670 763 Stray light correction type 2 greater than a threshold The 765 865 910 thresholds are defined by the other mission requirements EA NN ES EA 12 13 14 15 16 443NP 490 565 Stray light correction type 1 greater than a threshold The 70 763 765 865 thresholds are defined by the ocean color mission requirements 443P 670 763 Stray light correction type 1 greater than a threshold The 765 865 910 thresholds are defined by the other mission requirements POLDER level 1 Standard Product User manual page 32 Appendix H How to locate a particular pixel in the data file The pixels of the POLDER reference grid are arranged in the data file line by line and column by column The last record of the leader file includes an array Npix 3240 which gives the number of pixels in the data file for each of the 3240 lines of the POLDER grid This array can be used for a fast location of a particular pixel in the data file Let il and ico be the line and column coordinates of the pixel in the POLDER reference grid The POLDER measurements for this pixel are located in the data file in record number reco The following relation apply ih 1 ilo 2 gt Npix il lt recog lt s 1 5 Npix il il 1 il 1 One method to retrieve the pixel is to read all records which satisfy the relation above and to read the correspondi
5. temperature of the lens are given for each up to 130 acquisition sequence The two temperatures are for the internal lens L5 to L10 and the external lens L1 and 12 The record also contains the position speed vector and attitude parameters of the POLDER instrument for each up to 130 acquisition sequences and 9 images per sequence The 9 images correspond to the spectral bands 443P 443NP 490NP 565NP 670P 763NP 765NP 910NP 865P For each of the 3 polarized bands only the values corresponding to the central filter are given 5 12 characters are used because POLDER electronics allows the programing of a succession of 12 sequences which is then repeated POLDER level 1 Standard Product User manual page 13 The position and speed vectors are given in a referential fixed to the Earth with the Earth centre as the origin The Z vector is from the Earth centre to the North Pole X is from the Earth centre to intersection of the equator and the Greenwich line and Y ZAX The attitude parameters yaw roll and pitch are given as right handed rotation around respectively the X Y and Z axis of the orbital reference frame The Z vector is from the satellite to the Earth centre X is perpendicular to Z in the plan containing X and the satellite speed vector along the speed vector Y ZAX The default value no data for the date temperature position speed vector and attitude is 0 Position Type amp Content length Reco
6. 0 lat 0 5 POLDER level 1 Standard Product User manual page 24 N NINT 3240 y col NINT 3240 5 a 180 This POLDER reference grid is centered on the Greenwich meridian For the extraction and visualisation of POLDER data close to the 180 longitude line it may be easier to work with a similar grid centered on this meridian A simple formula allows to switch from one lin col coordinate system to the other lin col lin lin N NINT 3240 ny col 3241 N MOD col 2N 3241 where MODn returns the remainder of the integer division by 2Nj POLDER level 1 Standard Product User manual page 25 Appendix C Method for deriving the viewing geometry for each channel With the POLDER imaging concept the 15 spectral polarized measurements are acquired sequentially Therefore a given surface target is observed for the various spectral bands with slightly different viewing angles The differences are very small but can be significant for some applications which need a very high angular accuracy such as the atmospheric correction over the ocean The view zenith angle 99 VZA and relative azimuth y9 RelAzim which are given in the level 1 product are for the central filter i e 670P2 The two parameters DVZC A 8 cos and DVzS A 0y sin which are given for each viewing direction in the data file are necessary to derive these angles for other spectral bands 6j and qj The formulae are as f
7. 0 CY POLDER Level 1 Product Data Format and User Manual Ed 3 Rev 0 October 30th 2003 Prepared by F M Br on CEA LSCE with the collaboration of CNES Project Team Introduction rss st ee te Ce En Te UE 2 The POLDER instrument on ADEOS asc ah ERA ce NC 2 Spectral bande ressens an E 2 Polarization measurements 3 Spatial resolu OM ars 4 Data ACUISTA A a 4 Eevelol Processing ia Ai ios 5 Calibracion AAA ti tel es 5 Radiometric processing enrgia nn E A enterrer asset 5 Geometrie processing 6 Detinttions RSA a ana denim etes tn Oued 7 POEDER product identification ss 7 GOMA ad did 7 StOKeS parameters aaa rain en ee it a is tas 7 CAM A A e E 8 Leader Elle Formats defies RS a ad A a a edd A Te obs Wow Basa 9 General Struct re sl to tsa Sas at nes Unease atone nt es de 9 Feader file descriptor deta dis cnt cl ii Dotes dd 9 Header rai Met nie de 10 Spatio Temporal Characteristics ii LA ane fn AE 10 Instrument setting parameters 12 Technological paramet ts ee Monks Sa es a e nu ne 12 Data processing parameters 14 SCAM PSACLOTS tilda trente Miel 15 Annotations 53 16 E 15 Data File Format res A T nt a 17 Data file descriptor rss rs Re niet Aia 17 Data SNS RSR MS te oa 17 A ar Ar e Re Re AI 21 Acron yes RS ER Ce aexuatens creas aenccetsauueniashenectetss seseasnenetha 21 Appendix A Product identification 22 Appendix B POLDER Full resolution reference grid 23 Appendix C Method for derivi
8. D In the table above the last column indicates the resolution of the grid used for the corresponding product POLDER level 1 Standard Product User manual page 23 Appendix B POLDER Full resolution reference grid The POLDER Full resolution grid is used for level 1 products as well as surface parameters of the level 2 and 3 products The POLDER reference grid is based on the sinusoidal equal area projection Sanson Flamsted The step is constant along a meridian with a resolution of 1 18 degrees Thus there are 180x18 3240 lines from pole to pole Along a parallel the step is chosen in order to have a resolution as constant as possible The number of pixels from 180 W to 180 E is chosen equal to 2 x NINT 3240 cos latitude where NINT stands for nearest in teger linis 1 to 3240 from top to bottom col is 1 to 6480 from left to right Note that in the real world the coordinates of the neighbours of a given pixel lin col are not necessarily given by lin 1 col 1 It is necessary to account for the deformation of the projection with the longitude The following equations yield the latitude and longitude of a pixel given by its lin col coordinates in the POLDER reference grid lin 0 5 18 N NINT 3240 cos lat lon col 3240 5 1 lat 90 The following equations yield the lin col coordinates in the POLDER reference grid for a pixel of given latitude and longitude lin NINT 18 9
9. Mixed 50 indicator 14 41 ss E Pixel Quality Index See Appendix G Rough Cloud Indicator Clear 0 Cloudy 100 or Undetermined 50 ss ns om ge 0 Number of available viewing directions Ndir Ea 3 SOMA HE A REE EA In the following 1 id lt Ndir 45 46 SR Sequence Arrangement Indicator 4 43 id 4 EE Sequence Number in the orbit 5 sn 1 lt sn lt 130 4 This two bytes indicator describes for the 14 directions wether the acquisition sequence is type A or type B see the Instrument Setting record in the leader file bit 0 is for direction 1 bit 13 is for direction 14 bit 14 and bit 15 are not used The bit is set to 0 resp 1 for sequence acquisition type A resp B 15 This sequence number is needed to identify measurements which have been acquired simultaneously i e during one acquisition or to retrieve some information about the instrument position attitude and state during the acquisition information found in the Technological parameters record of the leader file 43 id 6 observed the pixel for filter 670P2 has observed the pixel for filter 670P2 0 43 id 8 43 id 9 43 id 10 43 id 43 id 43 id 43 id POLDER level 1 Standard Product User manual page 19 1 5103 View Zenith Angle for filter 8 670P2 16 6 103 Relative Azimuth Angle for filter 8 670P2 16103 A ycos Relative variation of viewing geometry between the filters See Appen
10. UT time of creation of the radiometric calibration input file yyyymmddhhmmssss Date and UT time of the beginning of applicability of the radiometric calibration yyyymmddhhmmss 313 320 Version of the data used for geometric processing ee rr Date and UT time of creation of the geometric data input file yyyymmddhhmms s Date and UT time of the beginning of applicability of the geometric data yyyymmddhhmmss NO m m mD POLDER level 1 Standard Product User manual page 15 353 356 B4 Product Confidence Data This field contains several indicators on the product quality 357 720 asa Scaling factors This record describes the coding of the parameters in the data file Most parameters are given using integer binary coding with either 1 or 2 bytes The physical values PV can be computed from the Binary Values BV through PV Slope x BV Offset The Slope and the Offset are given for each parameter in this record Position Type amp Content Length Record Number in the file 7 Length of this record 13140 9 16 Interleaving indicator BIP BIGS SENDIANSSSSSS as on IBM mainframes 33 36 37 44 2 26 ip 20 26 ip 32 ts sssssEtbb 26 ip 44 o 00000Etcc 8547 13140 Aus Annotations This record gives some statistical information on the results of the level 1 processing The percentages of land water and mixed pixels in the viewing segment are given A r
11. applied demultiplexing i e separation of the data from the different instruments The POLDER level 0 data are then sent to CNES where they are systematically processed up to level 3 The present document is only concerned with level 1 Calibration The POLDER instrument does not include any onboard calibration device The instrument calibration is achieved in flight using geophysical targets of known spectral and angular reflectance properties The calibration coefficients are monitored and updated during the satellite life Hagolle et al 1999 The calibration coefficients used for the level 1 processing are identified in the leader file Data processing parameters record by their version number The level 1 measurements are given in units of normalized radiance the radiance W m2 srl has been multiplied by x Ex where Ex is the extraterrestrial solar radiance accounting for the variations of sun Earth distance This choice rather than expressing the measurements in units of W m 2 sr 1 was made because the POLDER instrument is calibrated in flight against known reflectances rather than known radiances The normalized radiances data can be converted to reflectances by a simple division by the cosine of the solar zenith angle Radiometric processing The radiometric processing is based in part on the POLDER radiometric model described in Appendix F Radiometric processing includes Stray light correction e Sub
12. cord 180 1See Annexe A for the POLDER standard for filenames POLDER level 1 Standard Product User manual page 10 89 92 ET Length of the Data processing parameters record 720 4 4 4 i 4 I I 101 104 Number of Annotation records in the file 1 105 108 Length of the Annotation record 13320 109 180 Header The header record gives general information on the product and the models used for data registration Position Type amp Content Length Record Number in the file 2 Length of this record 360 9 24 Information Point Phone Number 25 40 41 48 49 56 Instrument identificator x 1 or 2 POLDER x Product identification PwWL1TBGl1ccecooov Satellite identificator x 1 or 2 ADEOSSxS 57 72 Spatial Coverage VIEWING SEGMENTS 73 80 81 110 Pixel size of the POLDER reference grid km 006 180 Name of the ellipsoid used for the data registration GEODETICSREFERENCESSYSTEM 1980 111 122 F12 4 Length of the ellipsoid minor axis meter 6356752 3141 123 134 F12 4 Length of the ellipsoid major axis meter 6378137 0000 135 164 Name of the Digital Elevation Model DEM used for the data registration TERRAIN BASE NOAA SSSSSSSSSSSS 165 172 Spatial resolution of the DEM along the latitudes in degrees aaa aaa 173 180 Spatial resolution of the DEM along the longitudes in degrees aaa aaa 181 360 A180 Spatio Temporal Cha
13. dard for product identification A standard POLDER product identificator 15 characters takes the form PwLxTyGzcccooov Browse level 1 or level 2 PwLxTyGzaammddv level 3 where Wis the instrument number 1 for POLDER 1 on ADEOS 1 2 for POLDER 2 on ADEOS 2 X indicates the product level 1 2 3 or 1 for the Browse product Y indicates the product thematic B as Basic for level 1 and Browse products R as Radiation and clouds L as Land surfaces or O as Ocean Color for Level 2 and 3 products Z is a code for product type see table below CCC is the ADEOS cycle number 1 lt ccc 999 OOO is the orbit number in the cycle 1 lt ooo lt 585 for POLDER 1 057 for POLDER 2 aammdd is the reference date for the temporal synthesis year month day V indicates the reprocessing number from A to Z Browse Tt st EAN E Peg fe TS Clouds amp Rad Budget 2 B medium Directional parameters surface Lzalolal run 2 Ocean amp Atm Non Directional param surface Lzalol B run LL Aerosols parameters 2 o c Medium Land amp Atm Clouds amp Rad Budget_ Synthesis 3 R B Medium Ocean amp Atm Marine parameters 3 of 8 rm 3 Aerosol parameters 5 O C Medium ai is Load A product consists of two files A leader file and a data file The leader file filename takes the form aaaL where aaa is the product identificator 15 characters Similarly the data file filename is aaa
14. dix C 1 6103 A 8ysin Relative variation of viewing geometry between the filters See Appendix C 10 4 Normalised Radiance for channel 443NP 43 id 43 id 4 43 id 43 id 4 43 id 43 id 21 43 id 22 43 id 23 43 id 24 43 id 25 43 id 43 id 43 id N N N Normalised Radiance for channel 670P Normalised Radiance for channel 763NP 43id 29 23id 3 43 id 30 Normalised Radiance for channel 765NP Normalised Radiance for channel 865P Normalised Radiance for channel 910NP Second component of Stokes Vector Q for channel 43 id 32 43 id 34 43 id 36 16 Due to the satellite velocity and the fact that the 15 measurements are not strictly coincident in time there is a small variation of view angle between the spectral filters See Annexe C for details POLDER level 1 Standard Product User manual page 20 43id 37 23 id 1 S12 104 43 id 38 43 id 41 43 id 42 43 id 43 43 id 44 43 id 45 43 id 46 43id 39 23id 2 SI2 10 4 43 id 40 SI2 104 23 id 3 i k 43 Ndir 47 Spare 648 Second component of Stokes Vector Q for channel 670P Second component of Stokes Vector Q for channel 865P Third component of Stokes Vector U for channel 443P Third component of Stokes Vector U for channel 670P Third component of Stokes Vector U for channel 865P POLDER level 1 Standard Product User manual page 21 Referenc
15. ers that select the spectral bands and polarization directions It carries 16 slots one of which is an opaque filter to estimate the CCD detector dark current The remaining 15 slots carry 6 unpolarized and 9 polarized filters 3 polarization directions for 3 different wavelengths Thus POLDER acquires measurements in 9 bands 3 of which are polarized Spectral bands Table 1 provides the spectral band characteristics for the POLDER instrument aboard the ADEOS 1 satellite The 9 bands are defined by their central wavelength spectral width dynamic range and polarization capabilities The saturation levels are given for two values of the acquisition integration time in unit of normalised radiance i e the maximum spectral radiance divided by the solar spectral ves No Yes Saturation level 105 1 ms saturation level 238 ms 097 ozs oss 10 ra 19 ni f 110 Table 1 Characteristics of the 9 POLDER bands The central Wavelength Ac is derived from the fy AS A T A aA POLDER spectral transmission T A and the solar spectrum S A A e f sA T A 02 POLDER level 1 Standard Product User manual page 3 irradiance at nadir and multiplied by x The dynamic reflectance range is subsequently obtained by dividing the range given in Table 1 by cos 0s where Os is the solar zenith angle Owing to the signal to noise requirements for ocean color measurements the 443 nm channel had to be split into a polarized band 3 fil
16. es Hagolle O Goloub P Deschamps PY et al Results of POLDER in flight calibration JEEE Trans Geosci Rem Sens 37 3 1550 1566 1999 Deschamps P Y F M Br on M Leroy A Podaire A Bricaud J C Buriez and G Seze 1994 The POLDER Mission Instrument Characteristics and Scientific Objectives JEEE Trans Geosc Rem Sens 32 598 615 ADEOS CCD CNES DEM ECMWF ERBE ISCCP LERTS LIA LOA LSCE LMD LPCM NDVI NRE NWM NASDA POLDER SIA TOA TOMS UT Acronymes Advanced Earth Observing Satellite Charge Coupled Device Centre National d Etudes Spatiales Digital Elevation Model European Center for Medium Range Weather Forecast Earth Radiation Budget Experiment International Satellite Cloud Climatology Project Laboratoire d Etudes et de Recherche en T l d tection Spatiale Long Integration Acquisition Laboratoire d Optique Atmosph rique Laboratoire des Sciences du Climat et de l Environnement Laboratoire de M t orologie Dynamique Laboratoire de Physique et Chimie Marines Normalized Difference Vegetation Index Normalized Radiant Exitence Numerical Weather Model National Space Development Agency of Japan Polarization and Directionality of the Earth Reflectances Short Integration Acquisition Top of the Atmosphere Total Ozone Mapping Spectrometer Universal Time POLDER level 1 Standard Product User manual page 22 Appendix A Product identification This Appendix describes the POLDER stan
17. g center this field and the next one are automatically updated in agreement with the area selection 4 is is the sequence number 1 is lt 130 POLDER level 1 Standard Product User manual page 12 Instrument setting parameters This record describes the integration time sequencing Short Integration Acquisition versus Long Integration Acquisition used for this viewing segment as well as the gain Position Type amp Content Length Record Number in the file 4 Length of this record 180 eel Short Integration Acquisition SIA duration ms mmm mmm 17 24 aes Long Integration Acquisition LIA duration ms mmm mmm 25 40 A16 Integration Time definition for sequence type A tttttttttttttttt with t S SIA duration or t L LIA duration The 16 characters correspond to the 16 POLDER filters in the following order Dark 443P1 443P2 443P3 443NP 490NP 565NP 670P1 670P2 670P3 763NP 765NP 910NP 865P1 865P2 865P3 41 56 Integration Time definition for sequence type B tttttttttttttttt with t S SIA duration or t L LIA duration Same as above Typical arrangement of sequence types A and B cecccccccccc ssS with c 1 Sequence type A or c 2 Sequence type B Examples 111111111111 All sequence acquisitions are type A 121212121212 Sequence acquisitions are alternatively type A and type B 73 74 Analogic gain number 159 7 75 180 ao Technological parameters In this record the
18. iance Ip and polarization direction x can be derived from Q and U through Ip Q2 U2 1 2 Ip sin 2x U POLDER level 1 Standard Product User manual page 8 Ip cos 2x 0 In the equations above the polarization angle x is defined with respect to the plane defined by the local zenith and the viewing direction Appendix D provides some equations to get the polarization direction with respect to the scattering plane Coding Most parameters of the leader file are written as formatted ASCII characters whereas the data file has a binary structure In what follows we make use of the following coding types Ax indicates an ASCII field of length x bytes Fx y indicates a real written on x characters with y digits after the floating point as in FORTRAN Ex F10 4 for 1234 5678 Ex y indicates a real written in exponential form on x characters with y digits after the floating point as in FORTRAN Ex E14 4 for 1234 5678E 08 Bx indicates a succession of bits for quality flags x is the number of bytes used I4 indicates a four bytes unsigned Integer from 0 to 232 1 SI2 indicates a two bytes signed integer from 32768 to 32767 12 indicates a two bytes unsigned Integer from 0 to 65535 SI1 indicates a one byte signed integer from 128 to 127 I1 indicates a one byte unsigned integer from 0 to 255 In the format description below the special character is used to indicate the space character Upper case let
19. its per viewing direction The first two bytes are for direction number 1 the last two bytes are for directions number 14 The data quality is nominal when all bits of the DOX are 0 Various causes may yield a degraded measurement quality which affect POLDER bands differently Moreover the various scientific objectives of the POLDER mission have different radiometric quality requirements This is why different thresholds have been set by the mission team to label a set of bands as nominal or degraded In the table below bit 1 is the least significative and bit 16 is the most significative The bit value is 1 if the condition is true Affected bands All Geometric corrections may be degraded ADEOS roll pitch or yaw greater than a threshold 1 670P No correction for near infrared band transmitance because 865P measurement is saturated or lacking 443NP No correction for optic polarization lack of 443P measurement 490 565 763 765 No correction for optic polarization lack of polarization measurements 910 6 Pixelsaturated lacking in the 4x4 window used for bicubic interpolation 670 CCD pixel may be degraded matrix border a CCD pixel may be degraded matrix border 11 7 443NP 490 565 CCD pixel may be degraded matrix border 670 7 6 63 765 865 910 CCD pixel may be degraded matrix border 443NP 490 565 Stray light correction type 2 greater than a threshold The 670 763
20. lose to tn 2 POLDER level 1 Standard Product User manual page 27 Appendix E ADEOS 1 and 2 orbital characteristics Local Time at origin of times 10 690525 10 3534 Correction factor for local time 0 0077771851 0 0361971 1 2939654e 05 4 949845e 05 3 9683356e 09 1 82803e 09 2 2428582e 13 0 ADEOS 1 and 2 are sun synchronous polar satellites The satellite subtracks are repeated with a period of respectively 41 and 4 days which defines an orbit repeat cycle During this period the ADEOS 1 and 2 satellite makes 585 and 57 revolutions around the Earth respectively The following equations allow an easy computation of equator crossing time local time at equator and date They make use of the Julian day which is an integer at noon The accumulated orbit number is defined as aaa ooo 1 Norb ccc where ccc and 000 are the cycle and orbit number respectively From aaa the longitude at the equator is given by lonEq lonEq0 aaa 360 C Norb The Julian day for the equator crossing time is given by Jul JO aaa C Norb sum 24 where sum corH 0 corH 1 aaa corH 1 aaa 2 corH 1 aaa 3 Inversely one can retrieve the accumulated orbit number from a Julian date Jday through bbb jday JO Norb C sum corH 0 corH 1 bbb corH 1 bbb 2 corH 1 bbb 3 aaa ROUND bbb sum 24 Norb C where ROUND returns the closest integer POLDER level 1 Standard Product User manual page 28
21. n the first and the third last measurement In order to compensate for y POLDER spectral bands 2500 2000 1500 ll 0 La y ha 400 500 600 700 800 900 Wavelength nm 1000 500 TOA Solar Spectrum W m um POLDER level 1 Standard Product User manual page 4 ADEOS satellite motion Ones Ones Ouen OED POLDER FOV Fig 2 spacecraft motion during the lag and to register the three measurements a small angle wedge prism is used in each polarizing assembly As a consequence the matrix image is translated in the focal plane to e oi Fig 3 Number of viewing directions available for each surface pixel Gray shades are from zero Black to fourteen white Twelve directions are available in the wide area around the satellite subtrack offset the satellite motion and the three polarization measurements are quasi collocated Spatial resolution The ground size or resolution of a POLDER measured pixel from ADEOS is 6 x 7 km at nadir Due to Earth curvature the viewing angle relative to the local nadir is larger than the viewing angle in the satellite reference frame Satellite angles Osat of 10 20 30 40 and 50 correspond to local viewing angles 0y of 11 3 22 6 34 19 45 7 and 57 8 respectively This leads to a slight viewing angle dependence of the pixel size leading to an increase of 21 for an incidence angle of 60 Data acquisiti
22. nerated from POLDER 1 measurement is identified by P1L1TBG1cccooov where ccc is the orbit cycle number ooo the orbit number in the cycle and v identifies the reprocessing number See Appendix A The leader and data filenames are pppL and pppD respectively where ppp is the 15 characters product identificator Geometry Four angles are included in the level 1 product e The solar azimuth s is relative to the local North direction It may vary between 0 and 360 The solar azimuth is 90 when the sun is East of the observed pixel e The solar zenith angle 64 is relative to the local zenith It may vary between 0 sun at zenith and approximately 80 e The view zenith angle Oy is relative to the local zenith It may vary between 0 POLDER at zenith and approximately 75 e The relative azimuth q is the difference in azimuth between the sun and the satellite directions ds5 oy where y is defined as ps with respect to the North direction p may vary between 0 and 360 6 is 0 360 for backscattering measurements and 180 for glitter observation San Zenith POLDER Stokes parameters In addition to the total radiance I the POLDER instrument measurements yield the description of the linear polarization for three spectral bands 443P 670P and 865P In the POLDER level 1 product this information is given as the second Q and third U components of the Stokes vector The polarized rad
23. ng column number Another faster method uses the dicotomy and it is shown below l h irecmax 1 Npix il il 1 reco 0 WHILE reco 0 AND irecmax 2 irecmin DO irec irecmax irecmin 2 if the ratio is not an integer perform an integer truncation READ record number irec and get the corresponding column number ic IF ic ico reco irec IF ic gt ico irecmax irec IF ic lt icg irecmin irec 1 END DO If recg 0 there is no data corresponding to the selected pixel in the data file
24. ng the viewing geometry for each channel 25 Appendix D Manipulation of polarization parameters 26 Appendix E ADEOS 1 orbital characteristics sn ane 27 Appendix F POLDER radiometric model 28 Appendix G Pixel Quality Index DQX sita ne a nd Sols Ma aca dln See 31 Appendix H How to locate a particular pixel in the data file 32 POLDER level 1 Standard Product User manual page 1 Last modified on October 30 2003 POLDER level 1 product Data format and user manual The concept of the POLDER instrument was imagined by several researchers from LERTS Laboratoire d Etudes et de Recherche en T l d tection Spatiale CNES Centre National d Etudes Spatiales and LOA Laboratoire d Optique Atmosph rique The concept was then validated using an airborne version built and operated at LOA The spaceborne POLDER instrument has been developed by CNES in partnership with industrial contractors The POLDER ground segment has been developed under CNES prime contractorship in conjunction with various industrial contractors and partners CEA LSCE and Meteo France Scientific algorithms are defined and validated by the following science laboratories Laboratoire d Optique Atmosph rique LOA e Laboratoire des Sciences du Climat et de l Environnement LSCE e Medias France e Laboratoire de M t orologie Dynamique LMD For questions or comments fmbreon cea fr
25. nterpolated on the POLDER reference grid using a bi cubic algorithm The POLDER ADEOS relative orientation is calibrated in flight using specific targets such as coastlines The attitude bias coefficients used for level 1 processing are identified in the leader file Data processing parameters record by their version number In the level 1 product the data are sorted by pixel of the Earth frame from North to South and from West to East For each pixel up to 14 sets of observations with varying viewing geometries are available The acquisition sequence number and the line column coordinates on the CCD matrix are available in the product which allow to reconstruct the original CCD acquisition as shown on the left image of Fig 4 The POLDER reference grid is described in Appendix B The grid has a constant resolution along the meridians 18 pixels per 1 latitude band and a variable resolution when expressed in degrees nearly constant in km along the parallels with the objective that all pixels have nearly identical areas POLDER level 1 Standard Product User manual page 7 Definitions POLDER product identification A POLDER standard product is composed of two files A leader file and a data file The leader file provides some information on the instrument and the data processing The data file contains the instrument measurements after radiometric and geometric processing together with ancillary data A Level 1 product ge
26. ollows 9 O cos po X DVzCY 8 sin po X DV2SY 2 2 lo 2X O9 cos q DVzC sin py DVzS x pvc DvzS arctan y id 8 cos po X DVzC IF Og COS po X DVZC lt 0 THEN qy j 180 where Xj is given in the table below MW PESE a EA E E A Note This formulation is based on the simple principle that the 15 measurements are acquired equally spaced and on a straight line in an angular system of orthogonal axis 0 sin p 0 COS POLDER level 1 Standard Product User manual page 26 Appendix D Manipulation of polarization parameters The POLDER level 1 product provides the second Q and third U parameters of the Stokes vector The Stokes vector is defined with respect to the reference frame defined by the viewing direction and the local zenith The polarized radiance Ip and polarization direction x can be derived from Q and U through lp 024 1023412 Ip sin 2x U Ip cos 2x 0 In the equations above the polarization angle x is referred to the plane defined by the local zenith and the viewing direction The following equations yield the polarization angle referred to the scattering plane defined by the sun and view directions x arctan U 0Q 2 IF Q lt 0 x x 1 2 sin tan a 714 cos 0 005 6 yaxa where y is the polarization direction defined with respect to the scattering plane Note that both y and y are defined modulo x In general y is c
27. on The POLDER instrument is in imaging mode on the sunlit part of the ADEOS orbit only Data acquisition starts when the solar zenith angle on the Earth surface at the satellite nadir is smaller than 75 and stops in the South when it is larger than 75 The acquisition sequence is repeated every 19 6 seconds A sequence is composed of 16 image acquisitions in the following order Dark 443P1 443P2 443P3 443NP 490NP 565NP 670P1 670P2 670P3 763NP 765NP 910NP 865P1 865P2 865P3 The total number of sequences in one orbit depends on the season and can be up to 130 The 16 filter sequence is repeated every 19 6s which corresponds to 4 rotations of the filter wheel During this POLDER level 1 Standard Product User manual page 5 interval a given point on the surface initially at nadir viewing moves by about 9 relative to the satellite Fig 2 The point remains within the POLDER field As the satellite passes over a target about 12 up to 14 directional radiance measurements for each spectral band are performed aiming at the point Figure 3 Therefore POLDER successive observations allow the measurement of the bidirectional reflectance properties of any target within the instrument swath Level 1 processing ADEOS data are received either at the Fairbanks Alaska Wallops Virginia or Hatoyama Japan receiving stations These data are then sent to the ADEOS processing centre where a preliminary processing is
28. ough cloud mask is applied to the data and the percentage of cloud covered pixels for each 10 latitude band first 90N 80N last 80S 90S is given Finally this record gives the number of observed pixels for each of the 3240 lines of the POLDER reference grid Record Number in the file 8 Length of this record 13320 Percentage of Dummy data found in level 0 ppp 0 lt ppp lt 100 8ip is the parameter number 1 lt ip lt 327 POLDER level 1 Standard Product User manual page 16 13 16 Percentage of saturated observations ppp 0 lt ppp lt 100 0 lt ppp lt 100 KARA Percentage of ocean pixels in the viewing segment ppp 0 lt ppp lt 100 M Gd iii ei 0 ppp 100 4 ib 25 Percentage of pixels recognised as cloudy in the 10 latitude band ib 4 ib 28 ppp 0 lt ppp lt 100 101 200 a100 Number of lines in the POLDER grid for which at least one pixel is present in the data file nnnn a Number of pixels or records in the data file for line il 4 il 204 A4 1 lt i1 lt 3240 from North to South nnnn 0 lt nnnn lt 6480 13165 13320 A156 9ib is the 10 latitude band number from North to South 1 lt ib lt 18 10Tf only a given geographical area is ordered from the POLDER processing center this field and the next one are automatically updated in agreement with the area selection POLDER level 1 Standard Product User manual page 17 Data File Format The Da
29. racteristics This records provides some information on the Earth temporal and spatial coverage for this viewing segment Position Type amp Content Length Record Number in the file 3 Length of this record 1620 POLDER level 1 Standard Product User manual page 11 Cycle Number ccc Orbit Number in the cycle 000 Sub satellite track number ttts spare Descending Node Longitude ddd ddd 0 360 Descending node date and UT time yyyymmddhhmmsscc spare Date and UT time of the first image acquisition for the viewing segment yyyymmddhhmmsscc Date and UT time of the last image acquisition for the viewing segment yyyymmddhhmmsscc Spare Number of sequences in the viewing segment 1 Nseq 130 Spare Line Number of the northern most pixel observed by POLDER in the viewing segment nnnn 0001 lt nnnns3240 Line Number of the Earth pixel located at the ADEOS nadir during POLDER acquisition of filter 670P2 of sequence fis nnnn 396 81 1 lt nnnn lt 3240 if l lt is lt Nseq nnnn 0000 if is gt Nseq Column Number of the Earth pixel located at the ADEOS nadir during POLDER acquisition of filter 670P2 of sequence fis nnnn po 1Isnnnmns6480 if l lt is lt Nseq nnnn 0000 if is gt Nseq 1441 1620 Ango 2 See Appendix E for ADEOS orbital characteristics and usefull relationships on cycle orbit and track numbers 3 If only a given geographical area is ordered from the POLDER processin
30. rd Number in the ile 5 Length of this record 166320 1278 is 12696 Sequence Number sss 0 lt sss lt 130 sss is if the 1278 is 1266 1278 is 1265 1278 is 1250 1278 is 1249 1278 is 1234 sequence was acquired and processed sss 0 otherwise Internal lens temperature during the sequence C Fttttttt ttttttt External lens temperature during the sequence C tttttttt ttttttt 1278 is 138 im 13717 Image Number i 0 lt i lt 9 i imif the sequence was 1278 is 138 im 1370 1278 is 138 im 1369 1278 is 138 im 1354 1278 is 138 im 1353 1278 is 138 im 1338 1278 is 138 im 1337 1278 is 138 im 1322 acquired and processed i 0 otherwise Date and UT time of the acquisition of image imin sequence is yyyymmddhhmmsscc X component of the POLDER position during acquisition of image im in sequence is km tppppppp ppppppp Y component of the POLDER position during acquisition of image im in sequence is km tppppppp ppppppp 1278 is 138 im 1321 1278 is 138 im 1306 1278 is 138 im 1305 1278 is 138 im 1290 1278 is 138 im 1289 1278 is 138 im 1274 1278 is 138 im 1273 1278 is 138 im 1258 Z component of the POLDER position during acquisition of image im in sequence is km tppppppp ppppppp Vx component of the POLDER speed vector during the acquisition km s l tvvvvvvv vvvvvvv Vy component of the POLDER speed vector during the acquisition km s71 tv
31. ta file is composed of a first record of length 180 bytes and a variable number of records equal to the number of pixels observed in the viewing segment Npixels Record Name Number of Record Length records Bytes Data file descriptor Data file descriptor This record describes the data structure of the data file Position Type amp Content Length Record Number in the file 1 Length of this record 180 9 20 Reference Document Identification PAST33131CN 21 26 Reference Document Version Number aa bb 27 32 33 36 37 52 Software Version Number aa bb File Number 2 File Namel PWL1TBG1cccooovD 57 60 Length of one data record 648 61 100 101 104 105 108 109 112 113 180 spare Length of the prefix in the data record bytes 713 Length of data in the data record 635 Length of the suffix in the data record bytes 0 53 56 Number of data records in the file 0 lt Npixels lt 1 2 106 Spare Data record A data record is composed of 11 non directional parameters including the prefix followed by 14 sets of 23 parameters 14 observation directions is a maximum for POLDER on ADEOS Most pixels have either 12 or 13 directional sets of observations other have less in particular on both ends of the viewing segment In the data record if less than 14 directions are available Ndir lt 14 the available directions are stacked 1141 is the line n
32. ters 443P and an unpolarized band 1 filter 443NP Each of the 3 polarized channels have large dynamic ranges whereas the unpolarized channel has a low dynamic range optimized for the ocean color mission While POLDER mission to investigate the cloud and radiative budget requires a large dynamic range in the measurements its ocean color mission requires a very precise radiometric resolution at low signal values During the instrument definition phase these two missions appeared to be in conflict It was therefore decided to add the possibility of using alternatively two dynamic ranges by changing the exposure time to the incident photons The measurements acquired with a Long Integration Acquisition LIA will have a better signal to noise ratio than with a Short Integration Acquisition SIA but will saturate more frequently The saturation levels given in Table 1 correspond to the two values of the integration time which are currently planned for SIA and LIA Polarization measurements For three of the eight spectral bands 443 670 and 865 nm a polarizer is added to the filters in order to assess the degree of linear polarization and the polarization direction These parameters are derived by combining measurements in three channels with the same spectral filters but with the polarizer axes turned by steps of 60 The three polarization measurements in a spectral band are successive and have a total time lag of 0 6 s betwee
33. ters are used for fixed fields whereas lower case letters are used for variable fields Spare fields are filled with repetition of the space character For binary parameters one or two values are reserved for Dummy and Saturated data They depend on the parameter format as indicated in the table below The Dummy value characterises missing data The Saturated value characterises out of range data Saturation is only expected for the parameters which are coded in SI2 Radiances and polarized radiances in the data records saturated am Dummy o 127 o 27 POLDER level 1 Standard Product User manual page 9 Leader File Format General structure The leader file is composed of 8 records of variable length Its total length is 195840 Bytes Leader file descriptor This record describes the data structure of the leader file Position Type amp Content Length 920 ar Reference Document Identification PASPI91310N5 21 26 as Reference Document Version Number aa bbS 2732 as Software Version Number aa bbs O Number of header record in the file 1 Number of Spatio Temporal Characteristics records in the file 1 65 68 14 Length of the Spatio Temporal Characteristics record 1620 leo 14 Number of Instrument setting parameters records in the file 1 73 76 14 Length ofthe Instrument setting parameters re
34. tion induced by the optics an effect which is nearly radial symmetric around the optical axis and null for the central pixel 6 varies with wavelength e a is the orientation of polarizer 2 with respect to the meridian plane see Fig 2 k1 k3 vue a and are two directions 60 from the orientation of polarizer 2 POLDER level 1 Standard Product User manual page 30 kl e and ES account for the departures of polarizers 1 and 3 with respect to their ideal positionning 60 from polarizer 2 Note that the formulation used in 3 yields 3 3 cos 2a 0 sin 2a 0 5 a 1 a 1 The signal modeling defined by eqs 1 to 4 was tested with laboratory measurements using an integrating sphere which provided incident unpolarized light and a transmission device capable of polarizing the incident light by a calibrated adjustable amount Level 1 radiometric processing yield the 1 Q U Stokes parameters from the CN a numerical counts The various calibration coefficients which are needed for this inversion have been measured before launch and are monitored in flight using geophysical targets of known reflectance spectral signature and polarization properties POLDER level 1 Standard Product User manual page 31 Appendix G Pixel Quality Index DOX The Level 1 data record includes an indicator of the pixel data quality This indicator is 28 bytes long which corresponds to 2 bytes 16 b
35. traction of dark current e Data calibration e Computation of Stokes parameters I Q U from the three measurements for the three polarized bands e Interpolation of the polarization parameters from the polarized to the unpolarized bands Correction of the measurements for the lens polarizing effects which depends on the input radiance polarization properties POLDER level 1 Standard Product User manual page 6 Geometric processing Fig 4 A single POLDER acquisition by the CCD yield a bidimensional image of a fractio ot the Earth left image For each channel a similar acquisition is repeated every 19 6 seconds and the fields of view partialy overlap The center image indicates the borders of every third acquisitions Level 1 processing integrates for each Earth pixel of the reference grid the POLDER observations up to 14 of this pixel and generateds a product where POLDER measurements are sorted by pixel from North to South and from West to East The image on the right is the result of an extraction from a level 1 product For each pixel the observation with the smaller view zenith angle was selected All POLDER standard products are Earth registered The geometric processing navigates the raw data which are registered in the instrument reference frame to an Earth fixed reference frame After projection on the Earth frame accounting for the ADEOS attitude and the POLDER ADEOS relative orientation the data are i
36. umber in the POLDER reference grid 1 il lt 3240 12 See Annexe A for the POLDER standard for filenames 3Note that the sum of the prefix data and suffix lengths do not yield the record length because there are 6 additional bytes before the prefix POLDER level 1 Standard Product User manual page 18 first and the end of the record is filled with Dummy values Note that the Ndir sets of measurements do not necessarily correspond to consecutive observation sequences In the table below the parameter number is the number used in the scaling factor record of the leader file As of January 1997 the Offset for the conversion of binary to physical values is 0 for all parameters The Slope is indicated in the table below At this time there is no plan to change these Slope values nevertheless a careful user should verify that they agree with the values given in the leader file scaling factors record e radiances an okes parameters are given in normalised radiance units the radiance in m sr The rad d Stok t uh lised radiance units the rad W m2 1 has been divided by the top of atmosphere incoming irradiance and multiplied by x It is necessary to divide the parameter by cos 8g to transform the measurement to reflectance units Position Param Type amp Slope Content Length Ce 0 ee ss m ength of this record bytes 628 zs r f rime Number ofthe pin the POLDER grid 9 10 Land 100 Water 0 or
37. vvvvvv vvvvvvv Vz component of the POLDER speed vector during the acquisition km s71 tvvvvvvv vvvvvvv 6is is the sequence number 1 lt is lt 130 7imis the image number 1 lt im lt 9 POLDER level 1 Standard Product User manual page 14 1278 is 138 im 1257 Yaw of the POLDER instrument during acquisition of image im 1278 is 138 im 1250 in sequence is tyyy yyy 1278 is 138 im 1249 a Pitch of the POLDER instrument during acquisition of image im 1278 is 138 im 1242 in sequence is ppp ppp 1278 is 138 im 1241 Roll of the POLDER instrument during acquisition of image im 1278 is 138 im 1234 in sequence is trrr rrr 166149 166820 A127 Data processing parameters This record provides information on the input data and the software version used to generate the Level 1 POLDER data Position Type amp Content Length 25 40 4150 57 64 A8 A8 A16 A16 A8 17 24 65 200 201 208 A136 A8 Levelt data creation country PRANCES 209 216 As Level 1 data creation agency cwessss 217 232 Ais _ Level 1 data creation facility CST POSSS SS9S55 233 248 Al Level data creation date and UT time yyyymmadhhmmss 249 256 las Level 1 processing software version ee rrs 257 272 Identificator of the POLDER Level 0 data used as input aaaaaaaaaaaaaaaa 273 280 Version of the data used for radiometric calibration ee rr Date and
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