AATSR Level 1b Processing: Status of Open Issues from the Calibration Review

1. AATSR Level 1b Processing: Status of Open Issues from the Calibration Review Andrew R. Birks Rutherford Appleton Laboratory Chilton, Didcot Oxfordshire OX11 0QX UK ENVISAT Validation Workshop, ESRIN, Frascati9 - 13 December 2002

2. Status of Open Issues from the Calibration Review • VISCAL algorithm • Level 1B Software Problem Reports • Auxiliary files • Potential L1b enhancements

3. VISCAL algorithm: • Original VISCAL algorithm did not work with real AATSR data because of undocumented differences in VISCAL monitor sampling between ATSR-2 (basis of test data) and AATSR • Solution: New algorithm (update to DPM) and new PC1 file. • PP updated July 02 • OP update pending (integration problems have delayed release) • VISCAL GADS will be absent from OP products until this revision is operational

4. Software Problem Reports (1) • SPR 1: Permutation of Auxiliary Temperatures in SPH • Closed: Corrected in the OP • SPR 2: Not applicable to Operational Processor • SPR 3: Typo in SPH field name • Closed: Corrected in the OP • SPR 4: SPH _mid_ parameters not compliant with DPM • Closed: Corrected in the OP • SPR 5: Discrepancy in final record of ADS #4 • Open but set aside for the present. Requires more information about the code. • SPR 6: Not applicable to Operational Processor

5. Software Problem reports (2) • SPR 7: Invalid scan in OP not in PP • Closed. Corrected in the IPF (Investigation of this problem also revealed an error in the DPM and PP; further review required in the longer-term) • SPR 8: Cosmetic fill missing from solar angles • Open. OP contractor need more time to add missing DPM step. A work-around to address the impact of this problem on cloud clearing is in place. Review of OP code use of solar angles also required.) • SPR 9: Invalid scans not flagged in SQADS • Closed . Corrected in the OP (related to SPR 7) • SPR 10: Cosmetic fill missing from nadir view scan numbers • Closed. Corrected in the OP

6. Auxiliary files: • Only 3 required revision at this stage: • ATS_INS_AX (to prevent spurious BBU temperature validation warnings): disseminated to PDS 29/10/02 • ATS_PC1_AX (for new VISCAL algorithm): will be introduced with new VISCAL code • ATS_CH1_AX (misalignment corrections, AOCS parameters and regridding tolerances): disseminated to PDS 14/11/02. May need further iteration in future

7. Proposed enhancements (1) • Exception flags • Pixel exception values are small negative values • At night, noise in the visible channels can mimic exception values • Causes confidence flags to be wrongly set • Potential solution: modify internal exception values • Possible methods to address this problem are being evaluated in the PP. Schedule for implementation in PP and OP not yet established

8. Proposed enhancements (2) • Regridding • Unfilled pixels in forward view caused by interaction of x - y geolocation errors with regridding algorithm changes • Modify x - y geolocation algorithm to reduce errors • Changes to CH1 file based on detailed review of X-y differences have significantly reduced incidence of cosmetic fill voids in forward view. Therefore a change to the algorithm itself is no longer considered a priority at this stage.

9. Proposed enhancements (3) • The present VISCAL algorithm assumes consolidated data, and only finds the VISCAL peak following the time of the OSV in the Main Product Header • A further revision to VISCAL search algorithm is therefore required to cope with the NRT data currently being distributed, in which peaks may precede the OSV • Prototyped, but documents and TDS not yet submitted to OP contractor (include in next “batch” of changes).