Assimilated SCIAMACHY NO2 fields HDF data file user manual
Contents
1. Error dataset i stop endif endfor no2 a_lev 0 nplev 1 no2 b_lev 0 nplev 1 endif transpose a_lev transpose b_lev if strmid vd_name 0 4 eq NO2_ then begin if vd_name ne start_time and vd_name ne end_time then begin track_date long64 strmid vd_name strlen vd_name 8 8 track_date track_date 1000 20000000000000 endif Check whether orbit fits in data structure if no2 norbits ge maxorbits then begin print no2 norbits print ERROR more orbits in file than maxorbits stop endif if count gt maxpix then begin print ERROR orbit no2 norbits 1 has more pixels count than maxpix stop endif Read fields into variables for j 0 nf 1 do begin hdf_vd_getinfo vd_handle j name fieldname size size type type strcompress fieldname remove_all execute nread hdf_vd_read vd_handle name fields fieldnamet if iret ne 1 then begin print Error dataset i stop endif name iret endfor Add variables to structure no2 date no2 norbits 0 count 1 no2 time no2 norbits 0 count 1 no2 lon no2 norbits 0 count 1 lon no2 lat no2 norbits 0 count 1 lat date time no2 no2 vcdtrop no2 norbits 0 count 1 no2 vcdstrat no2 norbits 0 count 1 no2 no2 no2 no2 no2 no2 no2 no2 no2 no2 endif vcd no2 norbits 0 count 1 sigvcd no2 norbits 0 count 1 sigvcdt no2 norbits 0 count 12. sigvcds no2 norbits 0 count 1 f1trop no2 norbits 0 count 1 psurf no2 norbits 0 count 1 sigvcdak no2 norbits 0 count 1 sigvcdtak no2 norbits 0 count 1 kernel no2 norbits 0 count 1 ghostcol no2 norbits 0 count 1 npix no2 norbits vcd sigvcd vcdtrop sigvcdt vcdstrat sigvcds fltrop psurf sigvcdak sigvcdtak transpose kernel ghostcol count if strmid vd_name 0 4 eq GEO_ then begin Check whether orbit fits in data structure if no2 norbits ge maxorbits then begin print stop endif if count gt maxpix then begin gt ERROR more orbits in file than maxorbits print ERROR orbit no2 norbitsti has more pixels count than maxpix stop endif Read fields into variables endif for j 0 nf 1 do begin hdf_vd_getinfo vd_handle j name fieldname size size type type name iret strcompress fieldname remove_all execute nread hdf_vd_read vd_handle name fields fieldnamet if iret ne 1 then begin print Error dataset i stop endif endfor Add variables to structure no2 sza no2 norbits 0 count 1 sza no2 vza no2 norbits 0 count 1 vza no2 raa no2 norbits 0 count 1 raa no2 ssc no2 norbits 0 count 1 ssc no2 loncorn no2 norbits 0 count 1 transpose loncorn no2 latcorn no2 norbits 0 count 1 transpose latcorn if strmid vd_name 0 4 eq ANC_ then begin
3. stratospheric vertical column density in 1e15 molec cm 2 Error in the stratospheric vertical column density in 1e15 molec cm 2 Flag that indicates if tropospheric retrieval was meaningful 0 yes 1 no Surface pressure of the pixel in Pa Error in total vertical column density without profile error contribution in 1e15 molec cm 2 Error in tropospheric vertical column density without profile error contribution i e when averaging kernel information is used in 1e15 molec cm 2 Averaging kernel of 31 fields corresponding to 31 pressure levels as defined in pressure_grid Ghost column defined as the total vertical column below the cloud top in 1e15 molec cm 2 GEO_ymmddttt contains 6 fields They are summarized below and commented on sza vza raa ssc loncorn latcorn satellite solar zenith angle satellite viewing zenith angle satellite relative azimuth angle defined as SCIAMACHY subset counter 0 Nadir 3 Backscan rejected 7 Last most westerly forward pixel longitudes of the four corners of the pixel latitudes of the four corners of the pixel ANC_ymmddttt contains 10 fields that are of meant for advanced users They are summarized below and commented on scd IASB slant column density from IASB in 1e15 molec cm 2 amf amftrop amfgeo scdstr clfrac cltpres albclr crfrac 1tropo total air mass factor used to compute vcd scd amf tropospheric air mass factor used to compute vcd
4. the alev blev and surface pressure numbers into pressure levels in Pascal representative of the layer of the averaging kernel The equation is p a_lev p_surf b_lev 1 and p surf is stored in the NO2_ymmdadttt The VData may contain as many as 20 maximum number of orbits in one day pieces of NO2_ymmdattt GEO_ymmddttt and ANC_ymmddttt The array NO2_ymmddttt is accompanied by a VData Table Attribute that contains the name of the track and the start and end time year month day hour minutes and seconds as follows VData Table Attributes track_identifier 30417035 start_time end_time 2003 4 16 23 42 57 2003 4 17 0 25 17 In this case the first track of April 17 2003 happened to start on the previous day but since it ended on April 17 it is attributed to this day The main data table is NO2_ymmddttt and it contains 16 fields They are summarized below and commented on date time lon lat vcd sigvcd vcdtrop sigvcdt vcdstrat sigvcds fltrop psurf sigvcdak sigvcdtak kernel ghostcol Date of SCIAMACHY retrieval yyymmdd Time of measurement h hmiss Center longitude of pixel Center latitude of pixel Retrieved total vertical column density in 1e15 molec cm 2 Error in the total vertical column density in 1e15 molec cm 2 Retrieved tropospheric vertical column density in 1e15 molec cm 2 Error in the tropospheric vertical column density in 1e15 molec cm 2 Assimilated
5. 10 Check whether orbit fits in data structure if no2 norbits ge maxorbits then begin print ERROR more orbits in file than maxorbits stop endif if count gt maxpix then begin print ERROR orbit no2 norbitst1 has more pixels count than maxpix stop endif Read fields into variables for j 0 nf 1 do begin hdf_vd_getinfo vd_handle j name fieldname size size type type name strcompress fieldname remove_all iret execute nread hdf_vd_read vd_handle name fields fieldnamet if iret ne 1 then begin print Error dataset i stop endif endfor Add variables to structure no2 scd no2 norbits 0 count 1 no2 amf no2 norbits 0 count 1 no2 amftrop no2 norbits 0 count 1 no2 amfgeo no2 norbits 0 count 1 no2 scdstr no2 norbits 0 count 1 no2 clfrac no2 norbits 0 count 1 no2 cltpres no2 norbits 0 count 1 no2 albclr no2 norbits 0 count 1 no2 crfrac no2 norbits 0 count 1 no2 1tropo no2 norbits 0 count 1 no2 norbits endif hdf_vd_detach vd_handle endfor hdf_close file_id end 11 scd amf amftrop amf geo scdstr clfrac cltpres albclr crfrac ltropo no2 norbits 1 References 1 Eskes H J and K F Boersma Averaging kernels for DOAS total column satellite retrievals Atmos Chem Phys 3 1285 1291 2003 2 Boersma K F H J Eskes and E J Brinksma Error analysis for tropospheric NO retrieval f
6. AMACHY comparison may want to map the modeled NO2 profiles via the averaging kernel to what SCIAMACHY would retrieve y is the retrieved quantity as follows y A x 2 with A the averaging kernel a 3l element vector specified at pressure levels described in the previous section and the vertical distribution of NO in partial subcolumns from a CTM or from colocated validation measurements at the same 31 pressure levels The user thus needs to either convert his or her vertical subcolumn NOz profile to the pressure grid of the averaging kernel in order to construct a vertical column y as would be retrieved by SCIAMACHY Note that the columns and errors Boersma et al 2004 given in the dat table are in 10 molec cm In principle a user may also interpolate the averaging kernel vector to the grid of his or her However since the AK is so sensitive to changes on small spatial scales for instance due to rapid cloud changes one should be very careful in interpolating the averaging kernel vector For these calculations the error in y will reduce to sigvcdak since uncertainties on the vertical NO2 profile are no longer accounted for A user should be aware that he or she should no longer use sigvcd because this error includes a retrieval specific profile error term that can now be discarded Alternatively a user may be interested in the tropospheric NO2 load alone For tropospheric retrievals with y now the tropospheric col
7. Assimilated SCIAMACHY NO fields HDF data file user manual Folkert Boersma and Henk Eskes 6 February 2004 Contents Content of the no2trackyyyymmdd hdf files The use of the averaging kernel IDL sample code to read the NO fields Content of the no2trackyyyymmdd hdf files The no2trackyyyymmdd hdf contains data on NO retrieved during one day The file is organised as follows e SDSGlobal Attribute containing data on the file e Vdata the actual data SDS Global Attributes An example of the SDS Global Attributes is given below Data_created_by refers to the version of the assimilation code used to produce the NOz fields SDS Global Attributes Name Value Author H J Eskes K F Boersma Affiliation KNMI Royal Netherlands Meteorological Institute Email eskes knmi nl boersma knmi nl Data_created_by TM3 NO2A version 1 01 Creation_date 15 Jan 2004 Unit_of_NO2_column 1e15 molecules cm2 VData The Vdata is organized as follows e pressure_grid from TM3 e NO2_ymmddttt contains the main NOg retrieval data for one track orbit e GEO_ymmddttt contains all geometric data associated with retrievals in this track e ANC_ymmddttt contains all ancillary data associated with retrievals in this track The VData always contains only one pressure_grid The pressure grid gives the 31 pressure levels that were used to compute the averaging kernel The VData Table Attribute gives the equation required to convert
8. axorbits maxpix float value 999 albclr make_array maxorbits maxpix float value 999 crfrac make_array maxorbits maxpix float value 999 ltropo make_array maxorbits maxpix int value 999 id hdf_sd_start file read The HDF_SD_FILEINFO procedure retrieves the number of datasets and global attributes in an HDF file hdf_sd_fileinfo id datasets attributes help datasets attributes iret 0 for i 0 attributes 1 do begin hdf_sd_attrinfo id i name name data d command name d iret execute command print Retrieved Attribute name d endfor hdf_sd_end id Open file and initialize vdata reading file_id hdf_open file read vd_id 1 vd_handle 1 end_of_file 0 vds hdf_vd_lone file_id nvds n_elements vds if nvds eq 0 then begin print ERROR No vdatas found in file stop endif Loop over vdatas for i 0 attributestnvds 1 do begin vd_id hdf_vd_getid file_id vd_id vd_handle hdf_vd_attach file_id vd_id read hdf_vd_get vd_handle nfields nf name vd_name count count fields fields Read pressure fields a_lev and b_lev into variables if strmid vd_name 0 4 eq pres then begin for j 0 nf 1 do begin hdf_vd_getinfo vd_handle j name fieldname size size type type name strcompress fieldname remove_all iret execute nread hdf_vd_read vd_handle name fields fieldname if iret ne 1 then begin print
9. orbits maxpix float value 999 9 sigvcd make_array maxorbits maxpix float value 999 9 vcdtrop make_array maxorbits maxpix float value 999 9 sigvcdt make_array maxorbits maxpix float value 999 9 vcdstrat make_array maxorbits maxpix float value 999 9 sigvcds make_array maxorbits maxpix float value 999 9 fltrop make_array maxorbits maxpix int value 999 9 psurf make_array maxorbits maxpix int value 999 9 sigvcdak make_array maxorbits maxpix float value 999 9 sigvcdtak make_array maxorbits maxpix float value 999 9 kernel make_array maxorbits maxpix nplev float value 999 ghostcol make_array maxorbits maxpix float value 999 9 sza make_array maxorbits maxpix float value 999 9 vza make_array maxorbits maxpix float value 999 9 raa make_array maxorbits maxpix float value 999 9 ssc make_array maxorbits maxpix int value 999 9 loncorn make_array maxorbits maxpix 4 float value 999 latcorn make_array maxorbits maxpix 4 float value 999 scd make_array maxorbits maxpix float value 999 amf make_array maxorbits maxpix float value 999 amftrop make_array maxorbits maxpix float value 999 amfgeo make_array maxorbits maxpix float value 999 scdstr make_array maxorbits maxpix float value 999 clfrac make_array maxorbits maxpix float value 999 cltpres make_array m
10. rom space J Geophys Res 109 doi 10 1029 2003JD003962 2004 12
11. trop scd scdstr amftrop geometrical air mass factor stratospheric slant column density amfgeo vcdstrat cloud fraction from FRESCO cloud top pressure from FRESCO surface albedo for clear part of the pixel from TOMS GOME database cloud radiance fraction i e percentage of light coming from the cloudy part of the scene level in TM3 where tropopause occurs The use of the averaging kernel Users will generally have a range of interests in employing the data We can basically distinguish straightforward users with a certain degree of faith in our measurements from more advanced users The last group is generally involved in detailed model to measurement comparisons and or satellite validation studies 1 Basic users will be mainly interested in the total NO column vcd and its error sigvcd and in the tropospheric column vcdtrop and its error sigvcdt These users may for instance want to qualitatively check preliminary results of some field experiment with the retrieved NO2 columns 2 Advanced users may be interested not only in the columns and their errors but also in the relation between the modeled or measured true vertical distribution of NO2 and the retrieved quantity These users will also want to use the averaging kernel that provides the link between modeled reality and retrieval for more details on the DOAS averaging kernel read Eskes and Boersma 2003 For example those who are interested in a model SCI
12. umn equation 2 reduces to y Atrop trop 3 with Atrop the averaging kernel for tropospheric retrievals defined as f Atrop A _ 4 amftrop and Ztrop the profile shape for tropospheric levels levels up to level number ltropo as specified in ANC_ymmddttt The pressure at level 1tropo does not necessarily correspond to the tropopause pressure but rather gives the pressure of the layer in which the tropopause occurs according to the WMO 1985 tropopause criterium IDL sample code to read the NO fields The following IDL program reads an HDF data file and stores the data in a structure no2 pro read_scia_no2 Read data from GOME HDF file between two times date1 and date2 and stores in structure no2 maxorbits maximum number of orbits in a file maxpix maximum number of pixels in an orbit nplevs number of pressure levels in TEMIS SCIA data Folkert Boersma KNMI February 2004 maxorbits 20 maxpix 5000 nplev 31 file no2track20030417 hdf Define structure for GOME data no2 norbits 0 npix intarr maxorbits a_lev make_array nplev float value 999 b_lev make_array nplev float value 999 date make_array maxorbits maxpix string value 999 time make_array maxorbits maxpix string value 999 lon make_array maxorbits maxpix float value 999 9 lat make_array maxorbits maxpix float value 999 9 vcd make_array max
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