GRWG/GDWG Web Meeting 2021-04-01

GSICS IR sub-group Web Meeting in lieu of Annual Meeting Session I - General Topics

In lieu of 2021 GSICS annual meeting , the IR group will host two (2) web meetings to review all the presentations of the annual meeting. The first one will be held at 12:00-3:00 GMT on Thursday April 1 2021 (check you time here) and focused on general topics on IR calibration. Should you have any urgent issues related to the IR group, please bring them for discussion.


Likun Wang NOAA Affiliate Plan of the IR Group Activities
David Tobin UW Inter-calibration of AIRS/IASI/CrIS
Thomas Pagano NASA/JPL AIRS Project Status
Martin Burgdorf Univ. of Hamburg Mercurial Calibration for IR Sensors
Larrabee Strow UMBC CHIRP, A New Homogeneous Hyperspectral Radiances Product at the NASA GESDIS Combining AIRS and CrIS
David Smith UK-STFC Status of the Sentinel-3 SLSTR performance and calibration
Alessandro Burini/Tim Hewison EUMETSAT SLSTR-IASI inter-calibration – application to oblique views and 3.7µm


CMA: Chengli Qi, Xiuqing Hu, Yong Zhang, Yuan Li

CNES: Clemence Pierangelo

ESA: Fabrizio Niro, Philippe Goryl, Steffen Dransfeld

ISRO: Pradeep Thapliyal

JMA: Kazuki Kodera, Arata Okuyama

KMA: Minju Gu, Dohy Kim, Eunkyu Kim, Jiyoung Kim

UMD: Hui Xu

UMBC: Larrabee Strow

UW: David Tobin, Bob Knuteson

EUMETSAT: Dorothee Coppens, Tim Hewison, Ali Mousivand, Alessandro Burini, Sebastien Wagner

IMD: AK Mitra

NOAA: Manik Bali, Fred (Xiangqian) Wu, Likun Wang, Fangfang Yu, Cheng-Zho Zou, Denis Tremblay, Erin Lynch, Flavio Iturbide, Hyelim Yoo, Mark (Quanhua) Liu, Andy Heidinger, Yong Chen, Zhi-Peng Wang

NASA JPL: Evan Manning, Tomas Pagano

NASA Langley: Ben Scarino

Universität Hamburg: Martin Jörg Burgdorf

UK-STFC: Dave Smith


Likun Wang (NOAA Affiliate) Review and Plan of IR Group Activities

As the IR sub-group chair, Likun Wang reviewed the key activities during last year for the GSICS IR subgroup. He also mentioned that a new chair needed after his three years’ term. The IR group will plan to host a monthly web meeting beginning this year, which will be held on Thursday in the first week of each Month.

Q: What are the procedures for the IR group chair nominations?

A: I am going to send out the email and set the deadline for nomination. Later, the candidate lists will be recommended to the EP for the final decision.

Q: Will the next chair be rotated among the agencies?

A: It is better but not necessary.

C(From Scott Hu): Can we organize a meeting to discuss which HIRS can be chosen as a reference instrument for reprocessing purposes?

A: Yes. It is good to bring the issue for discussion for a web meeting.

David Tobin (UW) Inter-calibration of AIRS/IASI/CrIS

David presented recent updates on inter-calibration of AIRS, IASI, and CrIS. He firstly mentioned the Report: "The Cross-track Infrared Sounder (CrIS) as a Reference for the Global Space-based Inter-Calibration System (GSICS)”, Version 2, 04 April 2020, which includes the pre-launch calibration traceability and radiometric uncertainty of CrIS. He then Recent Intercalibration examples, including 1) AIRS/IASI/CrIS SNO results 2) SNPP CrIS / NOAA-20 CrIS Double Differences and 3) SNPP CrIS /VIIRS long term time series.

Q: Based on the vertical scale of the plot, Is NOAA20 worse than SNPP (slide 4) for cold scenes?

For the cold target for TVAC, the instrument mostly “looked” at the reflected radiation from the background. This is why the vertical scale is expanded for the cold scenes. Along the row for different sensors, they are on the same scale.

Q: The inter-comparison results are for IASI-A (slide 7) only? How about IASI-B and IASI-C?

A: We have compared all of them. The results are similar. I can share the results as well.

Q: Slide 8: What’s 2X Apodization?

A: We try to remove the spectral pikes of BT differences between two instruments. The apodization has been applied two times to make the curve smooth. Therefore, we can focus on the radiometric difference between them.

Q: slide 9 Is IASI-B used as a transfer target?

A: Yes.

Q: Slide 12 Is the drift because of the side switch?

A: Yes. This is what I am trying to show.

A: Slide 12. Do you compare the trend for AIRS (with MODIS)?

A: Yes. We did similar studies for AIRS and MODIS.

Thomas Pagano (NASA/JPL) AIRS Project Status

Tomas gave brief updates on the AIRS project status, 1) AIRS is in excellent shape and is expected to continue to at least 2025, 2) radiometric calibration coefficients are updated for version 7, 3) AIRS Level 1C data V6.7 was released in March 2020 and V7.0 will be released in June 2021.

Comments (David Tobin): I have used the AIRS level1-C data for my study. It is very easy to use. I recommend that the community should use AIRS level1C data. It was a game change for the inter-calibration community after AIRS was launched.

Q: Did you compare the difference between AIRS and MODIS?

A: Yes. It was done by the UW group.

Q: Are there any documents available for AIRS level1-C data?

A: Please email me and I would like to provide the documents.

Martin Burgdorf (Univ. of Hamburg) Mercurial Calibration for IR Sensors

Martin presented a study of using the observations of Mercury and Venus in the edges of the FOV of imagers on geostationary satellites for channel-to-channel registration and point spread function characterization.

Q: For the channel-to-channel registration, can you see clouds, or the coast lines move when one plays two images from one band to another band?

A: Have not tried it. May be hard to see because different channels “see” different features.

Q: Can this method be applied for other polar-orbiting instruments?

A: Yes, if the instrument can see the area around the Earth. For thermal IR channels, it may not get enough of the signal. The observations of Mercury and Venus only have a few pixels and is limited to instrument the field of view.

Larrabee Strow (UMBC) CHIRP, A New Homogeneous Hyperspectral Radiances Product at the NASA GESDIS Combining AIRS and CrIS

Larrabee introduced a new dataset - CHIRP: A climate hyperspectral infrared radiance product combining the AIRS and CrIS Satellite Sounding Records. CHIRP will provide continuous hyperspectral radiance records from 2002-2040. He discussed the Radiometric stability of AIRS-CHIRP. The radiometric offsets among sensors (at fixed points in time) are estimated to be accurate to ~0.03K.

A: Can you Share with the Details for PCA reconstructions?

Q: There is the ATBD for AIRS level1-C data at NASA Website.

Q: Are you looking into the hot scenes for fire and hot land?

A: I did check it a few years earlier. You need to check the AIRS grid level data. It will be interesting.

Team discuss using the CHIRP AIRS product to generate FCDR as well as using it for re-processing inter-calibration between AIRS and other instruments.

David Smith (UK-STFC) Status of the Sentinel-3 SLSTR performance and calibration

David briefed the status of the Sentinel-3 SLSTR performance and calibration. His talk was focused on 1) monitoring of instrument parameters, 2) Monitoring of on-board calibration sources and 3) Satellite inter-comparisons, 4) Validation of L2 data products. He used the Tandem phase to investigate differences and validate uncertainties for S3A /B.

Alessandro Burini/Tim Hewison (EUMETSAT) SLSTR-IASI inter-calibration – application to oblique views and 3.7µm

Burini presented the inter-calibration results between SLSTR and IASI. The main features include 1) fast collocation for oblique view pixels, 2) test and validate the IASI gap filling method that extends the IASI spectra to 2760cm-1.

The talks by Dave and Alessandro are all related to SLSTR. Therefore, the questions are combined.

Q: What is the red line in slide 10?

A: It shows the sampling number of collocated pixels. It is the PDF distribution for different scenes.

Q: Slide 24: There is 305K saturated at 3.9 um band. (for Alessandro)

A: I received an email from you on this issue. Tim’s talk will further discuss it.

Q: Is SLSTR geolocation dataset applied for terrain correction? (For Dave) If yes, the collocation of IASI observations (without terrain correction) with SLSTR on the Earth surface off-nadir view probably has some uncertainties? So, it may be is better to collocate two sensors over space instead of on the Earth surface.

A: Yes, SLSTR geolocation dataset has been applied for terrain correction. I agree that, over mountainous terrain, the collocation may have some uncertainties.

These two talks are postponed to the next meeting.

Tim Hewison (EUMETSAT) Introducing the Hot Land Bias issue

Chengli Qi (CMA) FY-3E/HIRAS-II pre-launch calibration and instrument performance

Outcome Action

R.GIR.20210401.1 The CHIRP dataset - a new Homogeneous Hyperspectral Radiances Product at Combining AIRS and CrIS – is recommended for reprocessing and FCDR development if AIRS data are needed.
Topic revision: r5 - 13 Apr 2021, LikunWang
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