GRWG Web Meeting 2011-08-09

GSICS Web Meeting on Form of GSICS Correction - Diurnal Biases, Offset Terms and Other Dependencies


  1. Tim Hewison (EUMETSAT) – Handling Dependencies in the GSICS Corrections
  2. Fangfang Yu (NOAA) – How to deal with Diurnal Cycles and Midnight Calibration Biases in GSICS Corrections
  3. Tim Hewison (EUMETSAT) – Fixing Offset/Slope Terms in GSICS Correction - How and Why
  4. Tim Hewison (EUMETSAT) – Exploring algorithms for Meteosat-HIRS Inter-Calibration
  5. Tim Hewison (EUMETSAT) – Strategy for inter-calibration of satellite series - Choice of Spectral Correction


Chair: Tim Hewison

CMA: Xiuqing Hu, Xu Na

EUMETSAT: Tim Hewison, Sebastien Wagner, Rob Roebeling, Bertrand Theodore

JMA: Arata Okuyama, Yoshihiko Tahara, Hiroaki Tsuchiyam, Yuki Kosaka

KMA: Dohyeong Kim

NOAA: Fangfang Yu


Some of the GEO-LEO hyperspectral IR GSICS Corrections currently in demonstration mode and under development show significant variations during the diurnal cycle. This is mostly related to the midnight blackbody calibration problem. The current ATBD could be modified to produce separate corrections for the periods of the diurnal cycle affected by this problem. However, this will take time. Meanwhile, the Users' Guides for these products should clearly specify the range of conditions over which they are valid - in particular, the periods of the diurnal cycle. These periods can be derived from the analysis Fangfang presented. It is also recognised that a thorough uncertainty analysis of these products requires considerable time to produce. An alternative would be to perform an analysis of time series of the GSICS Corrections to provide a Type A evaluation of the random part of the uncertainty. GPRCs are encouraged to conduct such an analysis for both the 'normal' part of the diurnal cycle, and the part affected by the midnight calibration problem and report these in their Users Guide for these products. Further analysis should also be conducted to analyse the contribution of the following factors to the apparent diurnal cycles: incidence angle (to resolve any scan-dependence) and surface type.

The approach proposed by Tim Hewison to allow producers of GSICS Corrections to fix their coefficients (e.g. OFFSET=0 when it is not significant) was generally supported. Tim will prepare a modified ATBD to explain the process and distribute this, together with examples of the original and modified GSICS Corrections to the GRWG for review.

The representatives of the GRWG agreed a desire to develop a systematic approach within to the problem of developing "Spectral Corrections" to account for spectral response function differences between the monitored and reference instruments of inter-calibration products. Tim Hewison posed a series of questions to help develop a consistent approach to this issue. Although no final answers were agreed, several of these questions resulted in common responses from the meeting attendees. In particular, it was felt that multiple channels of the reference instrument should be allowed as inputs, although they should remain static throughout a given product, where possible. Similarly, the spectral correction should have the same form for each pair of satellite instruments (although some terms may become zero due to availability). Most importantly, it was felt that we should not allow any subjectivity in the selection of the form/channel combinations to ensure the inter-calibration products remain impartial to the producers' influence. This highlights the need to develop a systematic approach to the generation of these spectral conversion functions and the products derived from them.
Topic attachments
I Attachment Action Size Date Who Comment
GRWG-Hewison_Met-HIRS.PPTPPT GRWG-Hewison_Met-HIRS.PPT manage 3 MB 05 Aug 2011 - 08:37 TimHewison GRWG-Hewison_Met-HIRS.PPT
GSICS.diurnal.calibration.correction.pptxpptx GSICS.diurnal.calibration.correction.pptx manage 1 MB 08 Aug 2011 - 21:02 FangfangYu  
Handling_Dependencies_in_GSICS_Corrections.pptxpptx Handling_Dependencies_in_GSICS_Corrections.pptx manage 353 K 05 Aug 2011 - 08:36 TimHewison Handling_Dependencies_in_GSICS_Corrections.pptx
How_and_Why_Fix_Offset.pptxpptx How_and_Why_Fix_Offset.pptx manage 367 K 05 Aug 2011 - 08:36 TimHewison How_and_Why_Fix_Offset.pptx
Spectral_Conversion_Choices.pptxpptx Spectral_Conversion_Choices.pptx manage 199 K 05 Aug 2011 - 08:37 TimHewison Spectral_Conversion_Choices.pptx
Topic revision: r6 - 09 Aug 2011, FangfangYu
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