Page 1 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research SCIAMACHY Calibration status November '04 G. Lichtenberg et al. SRON - National Institute for Space Research Utrecht, The Netherlands

Page 2 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Outline  Radiometric calibration  Polarisation status  Light Leak  Dark correction  Evolution Bad & Dead Pixel mask  Summary of PCRs  Verification  Other open points  Conclusions

Page 3 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (I)  History:  Reflectance comparisons showed an offset of -15 to -20%  SMR comparison showed an irradiance 8 – 15 % too high  It was decided to re-calculate radiometric key data on basis of different measurements (NASA sphere & OPTEC msm's)  TPD and IfE re-calculated ABSRAD and ABSIRR, both results agreed  IfE found a deviation of the EL_AZ parameter (Limb mirrors) and BRDF and provided a correction  IfE calculated correction factors to be applied on OPTEC5 calibrated data and key data on a full wavelength grid solving some interpolation problems.

Page 4 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (II)  2 types of radiometric key data from IfE are available:  NASA sphere based  Spectralon based  Both key data sets were corrected for  Memory effect, Non-linearity, Spectral stray light (SRON)  In-flight NDF (SRON/IfE)  Correction of integration time in the IR (SRON)  Relative angle correction BRDF (TPD)

Page 5 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (III)  Verification method:  SRON processed (new) verification orbits with L0->1 processor provided by DLR for both IfE keydata sets and the original key data set  L0 files with SMR measurements close to the verification orbits are processed for both keydata sets and the newly calculated SMR is extracted by SRON  KNMI and RAL verify reflectances

Page 6 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (III)  Verification:  Comparison of solar irradiances with Kurucz show agreement within 3-5% for all channels except channel 1 (reason unclear) and channels 7,8 (ice)  Comparison done by KNMI with different solar reference show a 5% offset in channel 5  Comparison with reflectance model by KNMI shows good agreement for wavelengths from 320nm – 390 nm for Spectralon based key data  RAL will compare SCIA reflectances with GOME reflectances  Comparison with MERIS shows the 1-7 % offset in the range between 450nm - 900nm

Page 7 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (IV) Old key data (result by G. v. Soest & G. Tilstra (KNMI))

Page 8 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (V) 'NASA' key data (result by G. v. Soest & G. Tilstra (KNMI))

Page 9 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (VI) 'Spectralon' key data (result by G. v. Soest & G. Tilstra (KNMI))

Page 10 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (VII) Meris comparison (J. Accareta, KNMI)

Page 11 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Radiometric calibration (VIII)  Open points & Schedule:  RAL verification for wavelengths above 380 nm  Difference of BRDFs calculated with NASA and Spectralon data above 750nm (possibly external stray light)  For the next verification round (early 2005) Spectralon key data will be used  Reasons for spectral features in Spectralon key data  Baseline (to be tested on Level2):  ASM Diffuser spectra for DOAS type retrieval  ESM Diffuser spectra for retrieval where radiometric accuracy is needed

Page 12 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Polarisation (I)  Summary of polarisation calibration and application:  s/p and -45/+45 polarisation sensitivity were measured  Ratio of science detectors to PMD signal for different polarisation directions were measured  The discovery of the phase shift made it necessary to derive some parameters theoretically. IfE described a possible method in IfE-TN based on Mueller Matrices  This document was used to define algorithms to generate a set of key data  The DP uses the key data to define Mueller Matrices and thus calculating a polarisation correction factor

Page 13 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Polarisation status (II)  History:  After tests by J.M. Krijger showed some sign problems in the polarisation a common polarisation reference frame was defined in June '03  Greek key data and data processor were adjusted accordingly, solving some, but not all problems  Additional investigations by TPD showed 2 errors in IfE-TN A new set of key data was generated (current version).  These key data show some unphysical values in PMD1 and the PMDD/45 combination (used to determine U) does not work  IR polarisation determination is still hampered by transmission problems

Page 14 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Polarisation (III)  Further planning:  Key data side:  Check of IfE-TN by J. Skupin (IfE)  After check TPD will compare their algorithms to the findings and if necessary recalculate the key data once more  If no serious errors are found, new key data can be provided very soon  DP side:  all parties together that work currently on polarisation verification have to come together to review the current knowledge and define methods to find possible errors in the DP  KNMI (P. Stammes) and SRON will organise this

Page 15 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Light Leak  Results so far (analysis by R. v. Hees (SRON)):  Analysis based on February '04 Limb dark measurements  Channel 7 shows a light leak with an amplitude between 20 and 120 BU/s  The intensity distribution shows no spectral features  The light leak changes amplitude rapidly and not very predictably (the 1σ value is up to 49 BU/s)  No simple correlation with orbit phase was found  Further investigations are under way

Page 16 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Light Leak (II) - Amplitude R. v. Hees (SRON)

Page 17 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Light Leak (III) - Variation R. v. Hees (SRON)

Page 18 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Dark correction (I)  Proposal by ESA for orbital dark correction means:  NRT data will have a dark correction from data taken 14 orbits earlier  OL data will have correct dark subtraction  This is only an issue for channels 7&8 at times the transmission is varying  Proposal by ESA for correction dark variation over orbit  PCR33 (which asks for the inclusion of transmission variation) will not be implemented in this round, but later  Details have to be worked out  This is mostly an issue for channel 8

Page 19 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Evolution of Bad & Dead Pixel Mask (I)  Investigations by Q. Kleipool showed:  The Bad & Dead Pixel Mask (BDM) is not static, i.e. over time the number of bad & dead pixels increase  The likely cause is radiation damage by protons or other heavy particles (only gamma ray radiation was tested on-ground due to budget limits)  The long term development is not yet clear  The changing BDM can influence retrievals in the IR severely  SRON is capable of calculating a BDM for each orbit after SODAP  Currently it is investigated how a dynamic mask can be implemented in the operational processor chain

Page 20 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Evolution of BDM (II)  Development of BDM over last 8000 orbits:  Channel 6: increase by 35 pixels to 90 pixels total  Channel 7: increase by 100 pixels to 380 pixels total  Channel 8: increase by 95 pixels to 275 pixels total  One dead or bad pixel at the wrong position in a fitting window can change retrieval results significantly  Apart from a dynamical BDM mask a L2 fit window monitoring has to be implemented to change a fit window if too many bad pixels make retrieval impossible.  TN available at (go to the 'Documents' page).

Page 21 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Evolution of BDM (III)

Page 22 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Evolution BDM (IV)

Page 23 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Summary PCR (I)  The following L0->1 PCRs will be implemented in '04:  New Memory Effect & Non-linearity  Orbital darks  Availability of all solar spectra for L2 applications  Flagging of data taken during decontamination  Correction of integration times channel 6-8  Later implementation:  Throughput correction (this might be reversed when it is needed for a slitfunction correction).

Page 24 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Summary PCRs (II)  PCRs were implementation in '04 is unclear/will not implemented:  Slitfunction correction (ice): SAST group will work o this  Light Leak chanel 7 : No implementation soon, no correction available  Spatial stray light: No implementation soon, no correction available  Key data PCRs  Implementation of new radiometric KD possible (in time for reprocessing), if Level2 validation shows no major problems  Implementation of new polarisation key data possible (however it is not clear that this is needed)

Page 25 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Verification (I)  The following combinations of DP/key data will be calculated for verification orbits  Old DP/Old key data  Old DP/New radiometric key data  New DP/New keydata  Keydata versions  Radiometric: Spectralon key data, NDF in-flight  Polarisation: 3.1 Nadir Limb  MEC/NL: New values for new correction  Other: unchanged

Page 26 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Verification (II)  Schedule:  Originally planned: L1 verification workshop  No longer possible because IECF was not ready in time  New plan: Verification workshop early next year (January or February)

Page 27 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Other points  Other calibration issues:  DLR-IMF will work on an ice slitfunction correction within SAST  Corrections for memory effect, non-linearity and IR integration time were implemented in the DP  Transfer of knowledge for key data will start soon

Page 28 Validation Workshop, , IfE Bremen, G. Lichtenberg:Calibration status National Institute for Space Research Conclusions  The verification of radiometric calibration was done  The polarisation correction is currently checked  Light Leak in channel 7 proves difficult to correct  Details of the implementation of a dynamical BDM have to be discussed  Verification data will be available soon  Depending on Level2 results, new key data can be implemented  Calibration documents and more available at