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Geolocation Verification of SCIAMACHY Level 0 Data at University of Bremen, Germany

This analysis, conducted at the University of Bremen, focuses on the geolocation verification of SCIAMACHY Level 0 data. We assess data from various observational modes, including Nadir, Limb, Solar Occultation, Sun Fast Sweep, and Subsolar. Using ESA's CFI software, we compute geolocation while accounting for ENVISAT attitude and SCIAMACHY misalignment. Our findings show good agreement between expected and actual geolocation, although we observed shifts in Limb ground pixels in the northern and southern hemispheres. Preliminary conclusions suggest mispointing issues impacting accuracy.

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Geolocation Verification of SCIAMACHY Level 0 Data at University of Bremen, Germany

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  1. Geolocation Verification S. Noël IFE/IUP University of Bremen, Germany

  2. Analysis • Analysis is based on scanner readouts and orbital parameters taken from selected SCIAMACHY Level 0 data for several observational modes: • Nadir • Limb • Solar Occultation • Sun Fast Sweep • Subsolar • From these data geolocation is computed using the ESA CFI s/w. • ENVISAT attitude information and SCIAMACHY misalignment values are taken into account. • Results are compared with expected values (from DMOP/SOST web page) and corner coordinates from corresponding Level 1b product.

  3. Green = Expected ground pixels, Red = Level 0 scanner data, + = Corner coordinates from Level 1b product

  4. Green = Expected ground pixels, Red = Level 0 scanner data, + = Corner coordinates from Level 1b product

  5. Results • The geolocation from Level 0 data is in line with Level 1. • Good agreement between expected and actual geolocation for nadir • Limb ground pixels are shifted to the left (w.r.t. flight direction) on the northern hemisphere, to the right on the southern hemisphere.Around the equator the agreement is quite good. • As a consequence, limb-nadir matching across track is only partly achieved. • Similar azimuthal effects are seen in other measurement modes(Solar Occultation, Sun Fast Sweep, Subsolar). • An anomaly report has been issued; the problem is under discussion but not solved yet.

  6. Preliminary Conclusions • All observed effects can be explained by a mispointing in azimuthal direction. • Most likely explanation is a wrong or non-optimal yaw steering correction, but error in computation of geolocation may also not be excluded. • Points to be addressed for a further analysis: • How in detail do all corrections (misalignment, ENVISAT and SCIAMACHY yaw steering, etc.) go into the commanding of scanners? • Which values (in which coordinate system) are used? • What corrections need to be applied to the scanner readouts in the level 0 product before calling the CFIs? • How is misalignment handled by the CFI routines? Do they discriminate between ENVISAT and SCIAMACHY misalignment? (This is relevant for solar/lunar parameters.)

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