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GERB calibration status

GERB calibration status. J E Russell Imperial College. Outline. State of Edition data, calibration, geolocation and comparisons Monitoring of GERB2 (MSG1) calibration changes First look (‘sanity check’) at GERB-1 GERB-2 overlap data. GERB data.

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GERB calibration status

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  1. GERB calibration status J E Russell Imperial College

  2. Outline • State of Edition data, calibration, geolocation and comparisons • Monitoring of GERB2 (MSG1) calibration changes • First look (‘sanity check’) at GERB-1 GERB-2 overlap data

  3. GERB data • GERB level 2 (V003) ARG products were released as Edition 1 data from the ggsps at end May of this year • NANRG and BARG products should follow shortly • Current Edition record runs from 25 March 2006 to present less 40 days • Reprocessing of old data has begun • Details of ARG validation and calibration uncertainty detailed in quality summary

  4. GERB data: accuracy

  5. Geolocation Target accuracy 0.1 GERB pixel: Requires precise knowledge of where in the MSG spin (100rpm) data is acquired. Accuracy of spin timing information from MSG much poorer than specified, plus delay in obtaining spin structure axis misalignment information from EUMETSAT: interim solution is to match GERB to SEVIRI observations. Performance: most pixels matched to 0.5 pixel; 90% to 0.33 pixel; 75% matched to 0.25 pixel. Stability of optical model derived from retrieved geolocation 1% of cases 4% of cases 5% of cases 15% of cases 25% of cases 10% of cases 20% of cases 20% of cases Long term: develop hybrid analytical/empirical model for motion of spacecraft and satellite rotation. Not all aspects of geolocation behaviour currently understood

  6. Inter-comparison of GERB and CERES radiances Valuable collaboration between GERB and CERES, and thanks to CERES team for helping GERB project; Special scanning pattern enables CERES to view same surface pixel along same line of sight; Particularly important for highly anisotropic SW radiances Best fitGERB=1.02xCERES+3.5Wm-2sr-1 Best fitGERB=1.004xCERES-1.8Wm-2sr-1 SW LW <GERB>/<CERES>=1.05<GERB>-<CERES>=5Wm-2sr-1 <GERB>/<CERES>=0.99<GERB>-<CERES>=-0.8Wm-2sr-1

  7. GERB data: intercomparison

  8. Radiance comparison: scene dependency

  9. SW Calibration: monitoring filter transmission SW and TOTAL channel share same optics and detector, only difference is quartz filter used in the SW. Transmission of quartz filter monitored using solar diffuser sphere. SW and TOT observations used to detect changes in transmission

  10. SW Calibration: filter transmission April 2003April 2004April 2005April 2006 T(03) = 0.921 (SD 0.004)T(04) = 0.920 (SD 0.005)T(05) = 0.919 (SD 0.015)T(06) = 0.919 (SD 0.013) Possible 0.2% decrease in filter transmission TBD (need to rule out changes in the accuracy of the thermal component)

  11. Two GERBs in orbit • GERB on MSG has been operating for 3.5 y • This is nominal design lifetime, but satisfactory science data is still being acquired. Current plans will keep MSG-1 GERB as the operational instrument for as long as possible, probably until around May next year (decision depends on EUMETSAT and SEVIRI) • GERB-1 on MSG2 • Around 2 months of science data from 6.6 to 6.3 W (29th April – 6th July with some breaks for commissioning activities and special scans) • 1 month of science data from 0 longitude (19th July – 18th August) • More overlap operations planned for December 2006 /January 2007

  12. MSG-1 MSG-2 comparison • So far no MSG2 GERB data processed beyond level 1.5 (i.e. no unfiltered radiances, no fluxes and no geolocation by matching to SEVIRI) • Very basic check on their values has begun

  13. GERB1/GERB2 filtered radiance comparison SW G1 6.5W TOTAL G1 6.5W GREEN: All earth columns pixels 25:216 matched by Earth disk edgeWHITE: 60N to 60S 60E to 60WRED: 30N to 30S, 60E to 60W

  14. GERB1/GERB2 filtered radiance comparison TOTAL G1 0W SW G1 0W GREEN: All earth columns pixels 25:216 matched by Earth disk edgeWHITE: 60N to 60S 60E to 60WRED: 30N to 30S, 60E to 60W

  15. New detector measurements

  16. Summary • Edition 1 theoretical uncertainties 0.96% LW 2.25% SW • Geolocation: method (by matching) not ideal solution and can’t meet spec for some products – improvement and further information on spacecraft behaviour still required • Spectral response: Ongoing analysis of the GERB-CERES differences, including further measurements on flight spare detector to provide further input to detector spectral response, uncertainty and pixel-to-pixel variability • Quartz filter transmission stable to within 0.2% - possible trend being investigated and thermal contamination source considered • Variation in GERB/CERES ratio with scene type / SW radiance mirrored in GERB-like (i.e NB-BB) / CERES comparison: not a GERB spectral response issue (although offset can be) • Very early comparison between GERB1 and GERB2 provide sanity check on these data

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