GRWG/GDWG IR Web Meeting on 2021-12-02

GSICS Web Meeting on

Agenda

1. Yong Zhang (CMA) – Calibration and validation of FengYun satellite thermal infrared channels using unmanned surface vehicle at CRCS Lake Qinghai
2. Tim Hewison (EUMETSAT) - Updated Guidelines for Application of GSICS Corrections for Meteosat Imagers
3. Fred (Xiangqian) Wu (NOAA) - GSICS Corrections for NOAA inter-calibration Products

Attendees

Guest Chair: Likun Wang

CMA: Yong Zhang

ESA: ‪Stefano Casadio

JMA: Kazuki Kodera, Arata Okuyama, Misaki Eiki

KMA: Eunkyu Kim

EUMETSAT: Dorothee Coppens, Tim Hewison, Vincent Debaecker, Viju John

NOAA: Fred (Xiangqian) Wu, Likun Wang, Fangfang Yu, Denis Tremblay, Flavio Iturbide, Anthony Reale, Hyelim Yoo. Ninghai Sun

Universität Hamburg: Martin Jörg Burgdorf

Summary

Yong Zhang (CMA): Calibration and validation of FengYun satellite thermal infrared channels using unmanned surface vehicle at CRCS Lake Qinghai

Yong Zhang talked about Calibration and validation of FengYun satellite thermal infrared channels using unmanned surface vehicle at CRCS Lake Qinghai. He first introduced the instruments on the unmanned surface vehicle and its design. Then he discussed the method how to compare the ground-based measurements with the satellite measurements. Finally, he presented the preliminary results of CRCS lake Qinghai 2021. The results are focused on two channels (10.8 and 12.0 µm) for FY3D.

Fred Wu (Q): 1) The boat seems to measure the nadir radiances. Can it measure the off-nadir radiances? 2) for surface channels, the radiances mostly are from the surface? How do you use the RTM to control the angles and surface conditions?

Tim Hewison (C): You can install upward-looking radiometers to retrieve the upward radiation flux in the future. You can get the water vapor and cloud information using upward looking instruments.

R: LEO is for nadir and GEO is for off-nadir. We can’t control the angle on the boat.

Fred Wu (Q): Slide 18, Can you comment large bias for two channels, which are not consistent.

R: The two measurements are from the ground and satellite, respectively. There are so many factors that impact on the comparison results.

Likun Wang(Q): How do you handle emissivity?

R: It directly measure brightness temperature instead of bulk temperature. We don’t need deal with the emissivity here.

Fangfang (Q): Slide 17, I see the variation of the time series of inter-comparison results. Do you know what causes that?

R: At this point, I am not sure but will investigate this.

Tim Hewison: Updated Guidelines for Application of GSICS Corrections for Meteosat Imagers

He presented updated the Guidelines for Application of GSICS Corrections for Meteosat Imagers. He first reviewed the method how to perform the GSICS correction based on inter-calibration method. He also discussed how to handle the uncertainty propagation. The open issues on how to deal with multiple GSICS inter-calibration files are presented.

Fred Wu: GSICS Corrections for NOAA inter-calibration Products

He discussed the strategy of GSICS corrections from the NOAA inter-calibration products. He first reviewed the implementation procedures and mentioned this correction is optional for users. In addition, the ATBD on GSICS correction will be prepared to document the procedures on a theoretical basis. Finally, he raised a fundamental question – “what is GSICS correction, really?”.

The questions and comments are combined here because these two talks are focused on the similar topics.

Fangfang (Q): Slide 7 from Tim’s presentation, for multiple GSICS inter-calibration files, you mean use the linear method to combine all together.

R: I just try to raise the issues here and maybe we can think it further in the future. It is still open for discussion.

Likun Wang (Q): Is linear regression enough, especially for cold radiance range for some channels. e.g shortwave channels?

R (Fred Wu): Based on the previous studies, it is good enough. But we can provide quadratic terms, but the users can choose how and whether use it or not.

R (Tim): In general, we should come out polynomial terms with physical meaning for GSICS corrections.

Q (Fred): what is difference between harmonization or homogenization?

R (Viju John): Harmonization is for radiometric correction, while homogenization is to deal with spectral difference between instruments.

Q(Likun): what do the ISSCP products really care about, Harmonization or homogenization?

R: Harmonization. For spectral difference, they deal with at in their own way.

C (Tim): I encourage other agency to do the similar GSICS correction. I also like the term “harmonization”. In addition, when we put the GSICS correction there, we also introduce the uncertainties, which is worthy of discussion in ATBD.

Q(Likun): How frequently do these correction coefficients will be updated? How frequently do the users like to?

R(Fred): It is open for discussion. It depends on the users and data operators.

Outcome

A.GIR.20211204.1 Action to Fangfang Yu to introduce the terms of “Harmonization” or “homogenization” during the annual meeting and collect the feedbacks from other groups (e.g., VIS and MW).

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