1. Validation workshop, Frascati, 13 December 2002Page 1 SCIAMACHY products quality and recommendations Based on presentations and discussions during this workshop Presented by Ankie Piters

2. Validation workshop, Frascati, 13 December 2002Page 2 Level 1 Main features (nadir radiance): Polarisation correction is wrong ch7+8: –time dependent dark current –correction for transmission loss (ice) PPG, etalon wavelength calibration can be improved Unrealistic features near channel boundaries Geolocation: limb tangent height 1-2 km shift; geometry issues(?) Accuracy : Solar spectrum (irradiance): 8-10% larger than Kurucz in all channels Reflectance: –Ch 1&2: 5-10% smaller than GOME –Ch 3-5: 10-25% smaller than GOME –Ch 6-8: unknown Limb and occultation radiance: unknown

3. Validation workshop, Frascati, 13 December 2002Page 3 Level 1 (continued) Effect on level 2: Errors in calibration propagate into all level 2 products, O3 and NO2 columns to a lesser extent. Level 2 products from ch 7&8 are physically incorrect. Recommendations: give highest priority to solving the calibration and level 0-1 processing problems Calibration issues for limb and occultation radiances should be identified and resolved Calibration should be made operational in line with planning, including m-factors, regular optimized updates of sun-spectrum, dark currents, etc

4. Validation workshop, Frascati, 13 December 2002Page 4 Level 2: O3 columns Preliminary comparisons mainly based on SV 3.53; few co-locations Main features: AMF ~90 degr) Viewing angle dependance Wrong geolocations in meteo-products Wrong trace gas absorption cross sections and Ring spectrum used Current accuracy: For Oct/Nov 5-10% smaller than comparative measurements, better for high latitudes (SV 3.54: increase of ~8% in tropics; 2 orbits with SV 4.00 yield similar results to SV 3.53) temporal variation in the Antarctic ozone hole is well reproduced Current precision: Approximately 3%

5. Validation workshop, Frascati, 13 December 2002Page 5 Level 2: O3 columns (continued) Recommendations: Fix identified algorithm/implementation bugs. Update the algorithms such that products are consistent with GDP v 3.0 or better. Include viewing geometry and cloud information in meteo product

6. Validation workshop, Frascati, 13 December 2002Page 6 JC Lambert et al.

7. Validation workshop, Frascati, 13 December 2002Page 7 Level2: NO 2 columns Preliminary comparisons mainly based on SV 3.53: few co-locations Main features: AMF ~90 degr) Wrong trace gas absorption cross sections and Ring spectrum used Current accuracy: <~30 N: offset -10 15 mol/cm -2 >30 N: offset up to +3.5*10 15 mol/cm -2 SV 3.54 and 4.00 seem to be worse in SH, better in NH, TBC (only 2 orbits) Recommendations: Fix identified algorithm/implementation bugs. Update the algorithms such that products are consistent with GDP v 3.0 or better. Check use of proper climatology data base for AMF calculation

8. Validation workshop, Frascati, 13 December 2002Page 8 Level 2: columns of CH 4, CO, N 2 O, H 2 O, CO 2 Main features: Wildly varying values: operational product orders of magnitude off, CO 2 =0 everywhere Different orbital phases have different behaviour in average and scatter (jumps) Strong correlation with albedo for CO and CH4 Current accuracy: Current accuracy for these operational products can not be determined Scientific retrievals of CH4 show physically consistent values, but are still underestimated Recommendation: Improve the calibration, in particular the dark signal determination Identify possible errors in the level 1-2 algorithms making use of the knowledge obtained from the scientific retrievals

9. Validation workshop, Frascati, 13 December 2002Page 9 Scientific retrieval Uni Bremen

10. Validation workshop, Frascati, 13 December 2002Page 10 Level 2: columns of SO 2, BrO, OClO, H 2 CO These products were not in SV 3.51 - 3.53 (cal/val distribution): SV 3.54 contained SO 2, BrO, H 2 CO; SV 4.0 contained only SO 2. Main features: BrO too large (factor 10) SO 2 mostly negative (SV 3.54) H 2 CO right order of magnitude Recommendations: Make these products available for verification

11. Validation workshop, Frascati, 13 December 2002Page 11 Level 2: clouds and AAI AAI algorithm works well, but values sensitive to level 1 quality Operational cloud cover fraction and cloud-top pressure show unphysical patterns Scientific retrievals of cloud cover fraction and cloud-top pressure yield physically consistent values Recommendations: Improve calibration / level 0-1 processing Fix algorithm and implementation bugs in level 1-2 cloud cover algorithm Retrieve cloud-top pressures with one of the scientifically available algorithms, instead of using climatology

12. Validation workshop, Frascati, 13 December 2002Page 12 Limb profiles One OL-ASCII file with O3 and NO2 profiles has been delivered; Verification has barely started. Main features: Values below O3 peak are too low (sometimes negative) Altitude shift, also in scientific retrievals (see level 1) Accuracy: Current accuracy of the operational product is unknown Scientific retrievals of O3, NO2, and BrO profiles appear to be physically consistent Recommendations: Make OL limb profiles available and start verification

13. Validation workshop, Frascati, 13 December 2002Page 13 Conclusions: current status of level 2

14. Validation workshop, Frascati, 13 December 2002Page 14 Conclusions: general Verification and validation up to now have been hampered by: –Lack of data distribution towards cal/val teams, SODAP team, and IECF –Slow implementation of problem solutions The operational products do not meet the required accuracy. Scientific retrievals show that this is in many cases a result of errors in the calibration, in the operational algorithms and their implementation. Release of the current operational products is likely to damage the scientific credibility and subsequent usage of SCIAMACHY data.

15. Validation workshop, Frascati, 13 December 2002Page 15 Recommendations Solve problems associated with calibration and level 0-1 processing. One specific issue is related to frequent update of calibration and degradation parameters (IECF). Identify and select a suitable data set from SCIAMACHY co- located with validation measurements, to be reprocessed after every processor upgrade for validation. Update the ATBD, provide specification of changes between data releases, provide documentation about the data bases used by the processors (e.g. spectroscopy, climatology, etc). Identify possible errors in the level 1-2 algorithm making use of the knowledge obtained from the successful scientific retrievals Achieve a significant improvement in accuracy of level 1 and 2 products before releasing operational data to the general (i.e. non cal/val) scientific community.