Plans for interim data release J E Russell (Imperial)

Major issues and work plan at last GIST Level 2 geo shown to vary in quality, level 1.5 geo error shown to vary after optical model correction required –Fix to rectification removed some level 2 observed effects, NRT geo generally good to 0.5 pixel but may be up to 2 pixels out in regions –Additional issues identified for level 1.5 SW spectral response –Scene dependent differences c.f. CERES radiances up to 5% for ocean using original response –Recovered response shows 12% difference but no (?) scene to scene variation in error –Varying difference across the pixel array SW fluxes: spurious diurnal variation [20W], –need to implement ADM normalisation correction and aerosol correction over ocean – both of these now implemented but haven’t solved the problem LW fluxes: viewing angle dependent differences c.f. CERES [20W max night, 35W max day], –Parameterisation derived based on comparison to improve agreement to +/- 15Wm -2 for hot and +/- 5Wm -2 for cold scenes

Other issues and work plan at last GIST Unfiltering data base to be updated to radiances for SW, and extrapolated to 500um –Database recalculated for radiances, extraploation to be done Improvement to the cloud detection –In production

Current status and issues: Geolocation Status at GIST 22: Level 1.5 geo much improved by TSOL jitter information (CSOL) Generally stable, but jumps occur, particularly after satellite moves. Systematic difference from RMIB matching geolocation implies it isn’t at the required accuracy and adjustment of the optical model is needed. Indications Current status: Bug fix in RMIB matched geolocation means some re-evaluation is required Extra information (axis mis-alignment and orbit and attitude correction) and monitoring required Needed for release: Want independent check on level 1.5 geo to aid in the optical model adjustment. Needs monitoring. Ideally would use adjusted level 1.5 geo for release – REQUIRES: level 1.5 optical model optimising and geolocation monitoring plan

Spectral response Status at GIST 22: Comparisons for original response show scene and pixel dependent differences in shortwave c.f. CERES up to 5% From limited analysis it appears that recovered spectral response seems to show less scene to scene variation in different to CERES but results in SW radiances 12% too high for all scenes Current status: Re-analysis of ground measurements in ongoing, additional measurements (using a corrected procedure) will be made on a ‘non flight spare’ detector from the same batch as those on GERBs 1-4 in the next month. Interim solution: Use the recovered, extrapolated witness sample response if this removes scene dependent differences provide overall gross (‘B’-factor type) adjustment by comparison with CERES – REQUIRES: reprocess 2 months (summer and winter) data with these modified responses and compare to CERES (for both direct and SEVIRI based unfiltering)

Current status and issues: Unfiltering database Problem with SEVIRI narrow-band to broadband, can be addressed by regression based on measurements Original used fluxes / pi – an issue for clear sky ocean – new database produced and can be implemented LW requires extrapolation to 500um (currently 100um), still needs to be done

Interim data release: Timeline addressing radiance issues Geolocation –Improved optical model + orbit and attitude and axis mis-alignment –If the timescale of this is not feasible then reassessment of the NRT geo after bug-fix required to determine effect on radiance etc. – mostly within 0.5, but up to 2 pixels for some pixels, problems at sun-rise and sunset Updated calibration parameters from Imperial to RAL and RMIB – by May 21 st Update to RAL processing to include running gains RAL reprocessing run: 1 week Updates to RMIB spectral database and cloud detection MID JUNE? RMIB processing run of 2/3 month dataset: 2/3 months + 2/3 months Comparison with CERES for reprocessed data: –(a) for large homogenous areas to determine scene to scene differences –(b) if no scene dependent differences then on a pixel by pixel basis months

Current status and issues: Fluxes LW: Comparison of thermal fluxes with CERES shows mean differences c.f. CERES which are viewing angle dependent [20W night and 35W day max]: composite of parameterised corrections to the ADM based on day and night comparisons with CERES and MS5-7. – Gives +/- 15Wm -2 agreement on average in hot scenes and +/- 5Wm -2 for cold scenes. Instantaneous differences? –Alternative: study of theoretical correction based on this, more detailed IR scene ID can not be done for interim release (~6months work) SW: Spurious diurnal variation [20W], no comparisons with CERES yes?. –corrections applied as decided at last GIST but don’t solve the problem

Interim release Either used adjusted level 1.5 optical model geo and monitor for required further tuning, or NRT geo and accept occasional larger errors and variable quality around dawn and dusk. Use our recovered best guess detector spectral response (if removes scene dependent differences in SW) and determine B shortwave gain correction from comparison with CERES. Fix the thermal fluxes? [20W night and 35W day max]: composite of parameterised corrections to the ADM based on day and night comparisons with CERES and MS5-7. –Apply or just note error for interim release? TBD SW fluxes [spurious diurnal SW signal up to 20W], –note errors or find correction for interim release? TBD