Verification of level 2 is performed by many groups in good co-operation within the SCCVT

1. Overview of first level 2 verification resultspresented by Ankie Piters, KNMI, and Vincent Soebijanta, BIRA-IASB • Verification of level 2 is performed by many groups in good co-operation within the SCCVT • Special thanks to: • Jan Fokke Meirink, Marc Allaart, Renske Timmermans, Ronald van der A, Henk Eskes, Michiel van Weele, Jeroen van Gent, Pieter Valks, Jos van Geffen, KNMI • Jose Granville, Pierre Gerard, Jean-Christopher Lambert, BIRA-IASB • Anne Grete Straume, Richard van Hees, SRON • Albrecht von Bargen, DLR/IMF • Johannes Frerick, ESA For providing tools, pictures, and data for this presentation

2. Outline • Level 2 products • Verification Plans • First results

4. Verification plans • Objectives of level 2 verification: • Detect errors in the level 1-2 software; • Study the correctness/applicability of the algorithms; • Report on software and algorithm errors and propose changes. • Verification Tasks: • Detect non-physical values • Check for internal consistency • Compare with independent level 2 retrievals • Verification data: • Four orbits between 3 and 11 August have been selected for verification

5. Verification team • The level 2 verification team, chaired by ESA, consists of algorithm experts from: • DLR • IFE Bremen • KNMI • IUP Heidelberg • BIRA-IASB • SRON • NASA/GSFC • SAO

6. First results • First Near-Real Time level 2 products are available to the verification team since 2 weeks. They contain: • O3 from UV, O3 and NO2 from visible • H2O, N2O, CO, CO2, CH4 from NIR • Cloud and aerosol products • We still miss slant columns of BrO, SO2, OClO, and H2CO (wrong number of fitting windows)

7. Ozone column from UV

8. Solar zenith angle < 88 degrees

9. O3 Vertical Column Density

10. O3 Slant Column Density

11. O3 Air Mass Factor

12. O3 and NO2 VCD and AMF

13. Ozone column summary • two orbits of 11 august versus GOME: • We see the same large-scale patterns, no strange values for sza < 88 degrees • histogram of ozone values versus GOME (sza < 88 degrees): • Looks OK for ozone from UV • Ozone from visible much too high (level 1 calibration problem) • Backscan pixels comparable with Forward • Slant Column Density are consistent with DOAS algorithm • Quick-and-dirty comparison with four ground based stations, and with GOME co-locations: • SCIAMACHY ozone roughly 5-10% smaller than ground based stations (wrong cross sections used) • SZA > ~90 degrees: AMFs become negative and 0 (implementation bug) • Errors of less than 5% expected from wrong cloud cover fraction

14. NO2 columns

16. Blue: NO2 column < 0 Red: NO2 column > 1016 cm-2

17. NO2 column summary • NO2 values are realistic for sza < 88 degrees • Slant Column Density are consistent with DOAS algorithm • AMFs for larger solar zenith angles are negative and zero • Backscan pixels comparable with Forward • negative values in the tropics: was the same for GDP 2.4, on which this processor is based. Probable solution: fit H2O and O4 in the same fitting window (it worked for GOME)

18. Near InfraRed columns • Near InfraRed columns all have unrealistic values, probably due to problems with the level 1 calibration

19. Conclusions • The level 1-2 Near-Real Time processor is working and ozone and NO2 look as expected for sza < 88 degrees. • Some implementation bugs have been identified and can easily be fixed • Level 1 calibration issues cause problems for a proper level 2 retrieval, especially in the Near InfraRed