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WP 3 : Absorbing Aerosol Index (AAI) WP 10 : Level-1 validation

WP 3 : Absorbing Aerosol Index (AAI) WP 10 : Level-1 validation. L.G. Tilstra (1,2) , I. Aben (1) , P. Stammes (2) (1) SRON; (2) KNMI. SRON, 10-07-2008. WP10: level-1 validation: status of calibration. SCIA/6.0x: polarisation retrieval improvements (mostly bug fixes)

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WP 3 : Absorbing Aerosol Index (AAI) WP 10 : Level-1 validation

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  1. WP 3 : Absorbing Aerosol Index (AAI)WP 10 : Level-1 validation L.G. Tilstra (1,2), I. Aben (1), P. Stammes (2) (1)SRON; (2)KNMI SRON, 10-07-2008

  2. WP10: level-1 validation: status of calibration SCIA/6.0x: polarisation retrieval improvements (mostly bug fixes) Polarisation product improved for all PMDs, but especially for PMD 4 validation document (SQWG): SRON-EOS/RP/08-024, March 11, 2008 SCIA/6.0x: introduction of new radiometric key data Radiometric calibration improved in the absolute sense (smaller absolute errors) validation document (SQWG): SRON-EOS/RP/08-025, March 11, 2008

  3. SCIA/6.0x: spectral features introduced, most strongly in channel 2The spectral features were not present in the old key data. (These features are not caused by errors in the polarisation correction.)documents:KNMI-RP-2004-02,Nov. 1, 2004KNMI-RP-2004-03,Nov. 3, 2004(based on spectralon keydata)

  4. WP3: scientific AAI (SC-AAI) and operational AAI (L2-AAI) Improving L2-AAI:SC-AAI algorithm was copied into the L2-AAI code by DLR. Validation completed.L2-AAI now shows a 100% agreement with our SC-AAI (when the “additional” SC-AAI features/corrections are skipped).(The new L2-AAI algorithm will be included in level-2 data processor version 4.0) Additional features SC-AAI: • correction for calibration offset at t=0 (also for SCIA/6.0x) • correction for the obstruction in the FOV for westernmost scan mirror positions (problem affects data until April 2003) • correction for (scan-angle dependent) instrument degradation • proper flagging of (potential) sunglint situations • ozone column dependency of AAI taken into account

  5. Including ozone column dependence: background Looks ok and similar to TOMS / OMI / GOME-1 monthly AAI maps

  6. FEB–MAI: unrealistic high values of the AAI for high latitudes TOMS, OMI, GOME-1: reliable data only for –60° < latitude < 60° Still, the AAI values (in this time of the year) are suspicious  WHY?

  7. AAI retrieval: comparison with LUT database of model reflectances. vza, sza, razi, surface height, albedo are allowed to vary. However, ozone column variations neglected in AAI calculation (ozone column set fixed to 334 DU). Idea: maybe ozone column variations cannot (always) be neglected • Calculated new LUT database (including ozone dependence) • Provided access to TOSOMI (SCIAMACHY) ozone column data • Ozone column varied in the calculations

  8. So, ozone column dependence cannot be neglected after all (at least, not for all situations)

  9. With proper ozone dependence:  Problem solved (skipped orbits for which no ozone column data were available)

  10. Conclusions/plans WP 3/10 • Strong spectral features in the reflectance spectrum  study spectral behaviour • Variation in ozone column values cannot be ignored in AAI retrieval  also relevant for the GOME-2 AAI • Further study and improve the (scan-angle dependent) degradation • Validate improvements in L2-AAI (part of the “SQWG work”) • Improve the L2-AAI even further (improve the SC-AAI) • …

  11. Extra slides

  12. Absorbing Aerosol Index (AAI) and the residue • Definition of the residue: • where the surface albedo A for the simulations is such that: • no clouds, no absorbing aerosols : r < 0 • clouds, no absorbing aerosols : r < 0 • absorbing aerosols, no clouds : r > 0 • B. Definition of the AAI: • AAI = residue > 0 (where residue < 0 the AAI is not defined)

  13. SCIAMACHY SC-AAI data are available on the TEMIS website http://www.temis.nl Available data: GOME SCIA : 1995–2000 : 2002–2008

  14. Degradation: AAI in 2004:(monthly mean)Normal distribution of UV-absorbing aerosols. Similar to observations by TOMS. AAI in 2006:(monthly mean)Degradation of the opticsleads to anomalously highvalues of the residue / AAI.

  15. SCIAMACHY degradation in the UV WLS: White Light Source, internal calibration lamp “Light Path Monitoring” results for 340 and 380 nm: Status: 340 : -25.9% 380 : -17.6% (27-06-2007) Status: 340 : -11.3% 380 : -8.2% (27-06-2007) Status: 340 : -16.5% 380 : -10.3% (27-06-2007)

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