GRWG Web Meeting 2019-10-17

GSICS Web Meeting on GEO-GEO inter-comparison algorithms


  1. Fangfang Yu (NOAA) - Introduction
  2. Tim Hewison (EUMETSAT) – Can we Modify GSICS GEO-LEO IR ATBD to apply to GEO-GEO inter-comparisons?
  3. Dave Doelling (NASA) – GEO-GEO for VNIR
  4. Fred Wu (NOAA) – GEO-ring
  5. Hyeji Yang (KMA) - Inter-comparison of AMI and AHI IR channels


Guest Chair: Fangfang Yu

EUMETSAT: Tim Hewison, Sebastien Wagner and Viju John

JMA: Arata Okyuama, Yusuke Yogo and Kazuki Kodera

KMA: Hyeji Yang, Minju Gu and Eunjyu Kim

NASA: Dave Doeling and Ben Scarino

NOAA: Fred Wu, Fangfang Yu, Hyelim Yoo, Manik Bali and Larry Fynn


In the Introduction to the webmeeting, Fangfang Yu (NOAA) explained the difference between instrument calibration (L0->L1B, including re-processing) and data calibration (L1b harmonization/re-calibration).

Tim Hewison (EUMETSAT) stated the issues/challenges to extend the GEO-LEO algorithm for GEO-GEO inter-calibrations. Two key questions for the GEO-GEO inter-calibration: 1) what is required level of uncertainty, and 2) who is the user? Larry suggested using tie-point to define bounding box of collocation area (faster than calculating VZA for all pixels).

Dave Doelling (NASA) talked about the challenges in the VIS/NIR GEO-ring considerations: uncertainty in the radiometric calibration accuracy, SRF difference, BRDF (including sun-glint) and parallax impact. Parallax errors can be reduced by degrading spatial resolution, but uniformity filter still needed to remove outliers, which introduce noise – not bias.

Fred Wu (NOAA) used the ABI based GEO-LEO and GEO-GEO results as examples and pointed out that GEO-GEO is valuable tool for instrument calibration, yet not best tool to harmonize GEO imagers. Parallax, zenith angle, and climate variations lead to GEO-GEO differences at various time scales, and the SRF difference is the most difficult obstacle.

Hyeji Yang (KMA) reported the AMI vs. AHI IR inter-comparison results. The result of GEO-GEO can be dependent on the targets. It confirmed that the GEO-GEO difference over land may show variation during daytime (>0.5K for Australian desert) and comparisons over ocean should be recommended.

Conclusions: GEO ring is a constellation of geostationary meteorological satellite that provide complete coverage of the non-polar part of the Earth. GEO-LEO is better to harmonize GEO imagers, while GEO-GEO algorithm could be considered a GSICS deliverable as a tool to validate the harmonized GEO-ring. GEO-GEO is not proposed as GSICS products.

A.GCC.20191017.1: GCC to notify the GRWG Chair and the POCs of GSICS GEO satellite agencies for the coming ISCCP-NG workshop. (Completed)


Topic revision: r13 - 24 Oct 2019, ManikBali
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