GRWG/GDWG Web Meeting 2018-06-05, 1100 -1230 UTC

GSICS Web Meeting on Spectral Gap Filling in IR Sub-Group


To reponse three actions during the 2018 GSICS annual meeting at Shanghai 2018 and discuss the future direction on Gap filling methods.

A.GIR.2018.4d.1: Na (CMA) to compare with the JMA gap filling methods. To report at the next web meeting in 2-3 months.
A.GIR.2018.4d.2: Likun Wang (NOAA) to set up web meeting to discuss comparisons of gap-filling methods and plan way forward by June 2018.
A.GIR.2018.4d.3: Hui Xu to apply gap-filling method to IASI following to previous comment (two IASI data wt/wo gap).

CrIS Gap filling Coefficients

Version 1.0 of CrIS gap filling coefficients as well as the readme file, example IDL codes are archived at,

If you have any questions, please contact Hui Xu at or Likun Wang at


  1. Likun Wang (UMD/NOAA Affiliate) – Introducation (5 min)
  2. Hu Xu (UMD) - CrIS Spectral filling method inter-comparison Using IASI data as Proxy (15 Min)
  3. Na Xu (CMA) - CrIS Spectral filling method test on FY-3D MERSI 8.5μm band (15 Min)
  4. Wan Wu and Xu Liu (NASA/Langley): Spectral Filling Method using PCRTM datasets (15 Min)
  5. Tim Hewison (EUMETSAT): Ideas to extend observed IASI spectra beyond 2760 cm-1 (10 Min)
  6. All: Discussion and Moving foreward (5 Min)


Guest Chair: Likun Wang (NOAA Affiliate)

CMA: Na Xu, Scott Hu, Yong Zhang

EUMETSAT: Tim Hewison, Vijiu, Alessoandro Burini, Seb Wagner

JMA: Masaya Takahashi, Yusuke Yogo, Tasuku Tabata and Kazuki Kodera

KMA: Minjun Gu, Hyeji, Enukyu

NASA: Wan Wu (NASA Affiliate), Xu Liu, Ben Scarino

NOAA: Likun Wang (NOAA Affiliate), Fangfang Yu (NOAA Affiliate )

UMD: Hui Xu


Likun Wang (NOAA Affiliate ) welcomes all the participators and reviews the history, challeges, and the methods for the IR spectral gap filling methods.

Hui Xu (UMD) presents the results of CrIS spectral filling method using IASI as a proxy dataset to response the actions from last web meeting. An analysis of the residuals confirmed they are not scene-radiance or scan-angle dependent for the 10.8µm channel (except over the Sahara) or the WV channel (except over DCC). However, the 3.9µm channel showed large variations - Masaya confirmed his Type B uncertainty analysis also showed large variability in this channel for cold scenes.

Wan Wu (NASA Affiliate) proposes the new gap filling method based on PCRTM spectral database. He suggests using unapodized CrIS SDR data will be more accurate for inter-calibration of narrow or broad-band instruments, and explained that this method can be applied before or after convolution and be used to extend the IASI spectra coverage. Likun stated a preference for application before spectral convolution. When asked whether the impact of spectral resolution had been examined, Xu Liu (NASA Langley) explained this this had already been done in the solar band as part of the support for CLARREO Pathfinder - and could also be done for the IR, given sufficient justification (e.g. to support GSICS). It was suggested that this database could be combined with Hui's PC regression method. This led to a discussion on sharing data and code, which led to the actions below.

Na Xu (CMA) presents the results that apply the CrIS gap filling coefficients to FY-3D MERSI 8.55μm channels, which looks very encouraging. It was pointed out that this channel may be sensitive to SO2, so results may be compromised in areas of strong volcanic activity.

Tim Hewison (EUMETSAT) presents some ideas on IASI extended spectral gap at shortwave regions. These incldued the exploitation of NWP data embedded in the SLSTR L1b data. One of the proposed methods was based on performing double differences between observed and modelled radiances for the equivalent channels on SLSTR and SEVIRI - although concerns were raised that the cancelation of model errors is unlikely to be complete. He suggested working with Wan Wu's modelled spectra as input data. It was also suggested that these developments should initially focus on night-time data.


GIR.20180605.1: Masaya Takahashi (JMA) to share original 9 LBLRTM-simulated spectra that are used for JMA gap filling methods.


GIR.20180605.2: Hui Xu (UMD) to test IASI calibration error effects on CrIS gap filling method.

GIR.20180605.3: Hui Xu (UMD) to work with NASA on IASI shortwave extended gaps and generate first version coefficents for night time observations if possible (before 2018-09).

GIR.20180605.4: Wan Wu (NASA Affiliate) to test different apodization methods for CO2 absoption channels.

GIR.20180605.5: Xu Liu (NASA) to share LBLRTM database in the community in a practical way (dependent on later discussion).

GIR.20180605.6: Likun Wang (NOAA Affliate) to work together with NASA to delivery GOES-R/ABI collocation dataset.

I Attachment Action Size Date Who Comment
CrIS_Gapfilling_Evaluation_GOES-ABI_20180604_HuiXu.pptxpptx CrIS_Gapfilling_Evaluation_GOES-ABI_20180604_HuiXu.pptx manage 5 MB 05 Jun 2018 - 02:22 LikunWang  
Interl_cal.pptxpptx Interl_cal.pptx manage 13 MB 05 Jun 2018 - 02:26 LikunWang  
Lblrtm9Spectra4GeoLeoIr.tar.gzgz Lblrtm9Spectra4GeoLeoIr.tar.gz manage 167 MB 19 Jun 2018 - 00:14 MasayaTakahashi LBLRTM-simulated spectra for GEO-LEO-IR JMA Gap Filling method
Likun_Wang_Review_Gap_filling.pptxpptx Likun_Wang_Review_Gap_filling.pptx manage 707 K 05 Jun 2018 - 03:38 LikunWang  
NaXU_CrIS Spectral filling method test on FY-3D MERSI 8.5μm band .pptxpptx NaXU_CrIS Spectral filling method test on FY-3D MERSI 8.5μm band .pptx manage 6 MB 05 Jun 2018 - 02:27 LikunWang  
SLSTR 3.7µm channel - IASI.pptxpptx SLSTR 3.7µm channel - IASI.pptx manage 1 MB 05 Jun 2018 - 09:18 TimHewison  
Topic revision: r18 - 03 Apr 2023, LikunWang
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