GRWG IR Sub-Group Web Meeting 2017-06-27

GSICS Web Meeting on IR Reference Sensors - IASI Changes & Traceability & Uncertainty Report


  1. Dorothée Coppens (EUMETSAT) - IASI-A Orbit Drift, End of Life and Non-linearity Corrections
  2. Tim Hewison (EUMETSAT) - Coordination of Traceability and Uncertainty Report
  3. Elsa Jacquette (CNES) - IASI uncertainty budget
  4. Tom Pagano (JPL) - A new preliminary set of calibration coefficients with uncertainty estimates for AIRS based on pre-flight and on-board calibration
  5. George Aumann (JPL) - Validation of AIRS calibration - Postponed
  6. Denis Jouglet?(CNES) - Inter-comparison uncertainty budget - Postponed
  7. Dave Tobin (NOAA/SSEC) - Tabulation of inter-comparison results - Postponed


Chair: Tim Hewison

CMA: Xiuqing ("Scott") Hu, Chengli Qi, C.Q. Wu

CNES: Elsa Jacquette

EUMETSAT: Tim Hewison, Dorothée Coppens, Frank Ruethrich

JMA: Masaya Takahashi

KMA: Dohyeong Kim

NASA-JPL: Tom Pagano

NOAA: Xiangqian ("Fred") Wu

RAL: Dave Smith

U-Wisc/SSEC: Joe Taylor

Previous meetings on this topic: - Discussion item 7d at 2017 GRWG/GDWG meeting ( minutes)


Dorothée Coppens described the plans for IASI-A, -B, and -C, as this issue is critical for the IR reference sensor traceability and uncertainty. However, it is also important for all GPRCs processing IASI data to consider:
  • Metop-A performed its last Out-of-Plane manouevre in August 2016
    • - Its orbit will start drifting now
    • - slowly becoming more elliptical and
    • - its equator crossing time will start to drift from 21:30 to 18:30 by 2022, slowly at first, then accelerating

  • The impact on the IASI-A calibration is expected to be small initially
    • But it will be carefully monitored
    • IASI-A should still be useful for NWP until at least 2021
    • End of Life tests will then follow until de-orbiting in 2022

  • CNES have developed improved non-linearity corrections (onboard) for all IASIs
    • Based partly on comparisons with other instruments (esp CrIS )
    • Impact is only on Band 1 and is largest at the longest wavelength channels
    • Change will make IASI-B warmer by ~0.2K (depending on wavelength, radiance & FOV number)
    • Change will make IASI-A warmer by ~0.1K (depending on wavelength, radiance & FOV number)
    • Residual uncertainty of correction is small (~0.01-0.02K)
    • It is not possible to perform a full correction on ground, so no reprocessing is planned.
    • Elsa will distribute a document describing the changes, based on her IASI2016 Conference paper

  • EUMETSAT are proposing implementing these as follows:
    • IASI-C from launch (2018Q4)
    • IASI-B from 2017Q3
    • IASI-A from 2018Q1 (6 months after IASI-B)
    • Schedule represents compromise between optimising NWP and climate uses
    • It was agreed this timescale allows impact of change to be analysed before Metop-A orbit drifts too much

  • GSICS needs to:
    • Introduce more careful monitoring of IASI-A and share reporting
      • - e.g. by double-differencing with other reference instruments
    • Plotting tool can currently only compare results with individual reference sensors
      • But can be used to visually compare these
      • - e.g. Meteosat-11 12µm at 285K wrt IASI-A, IASI-B
      • Other GPRCs are encouraged to upload products derived from multiple reference sensors to the servers
      • EUMETSAT have an outstanding action to investigate plotting double-difference.
    • Decide when to switch to IASI-B as the reference!
    • Decide how to switch to IASI-B as the reference!
EUMETSAT will continue to monitor IASI-A/B double difference against Meteosat/SEVIRI. CMA, KMA, NOAA and JMA will perform the same analysis based on their respective GEO imagers. All 5 agencies will report the results in a common format, following the example of the database for the Infrared Reference Sensor Inter-Comparison Summary. Confirmed contributors are as follows:
  • Tim Hewison (EUMETSAT)
  • Masaya Takahashi (JMA)
  • Dohyeong Kim (KMA)
  • (CMA)
  • Xiangqian ("Fred") Wu (NOAA)
Tim Hewison provided an update on the (slow) progress with the Report on "Traceability and Uncertainty of GSICS Infrared Reference Sensors".
  • It was agreed to report the uncertainties and relative differences between sensors as brightness temperatures differences,
  • evaluated for scenes ranging from 200-300K at 10K intervals,
  • and at 10cm^-1 intervals, calculated from hyperspectral radiances, following the methodology previously described by Denis Jouglet.
  • It was further suggested that the accornym "IRRefUTable" be informally adopted as a shorthand to refer to activities related to this report.
Elsa Jacquette described the process of revising the IASI uncertainty budget, which is planned for this year.
  • She will circulate a draft by September, for inclusion as part of the planned presentation on the "IRRefUTable Report":
  • Joe Taylor confirmed that Dave Tobin's recent updates ot the counterpart analysis for CrIS still follow the same basic approach as described in his paper, which should serve as an example for AIRS and IASI - although some of the values have been updated.
  • Traceability to SI standards was discussed.
    • Although it is possible to establish this during pre-launch testing, the traceability chain is broken during launch and is not possible to re-establish with the current instruments.
    • Furthermore, it is difficult to quantify the uncertainties associated with all the changes since pre-launch testing.
    • However, the IRRefUTable report attempts to establish IASI, AIRS and CrIS as Community Reference Standards.
Tom Pagano presented a draft of the v7 of the AIRS calibration.
  • This is the first update since launch.
  • The biggest change is in the treatment of the scan mirror reflectivity-polarisation interaction.
  • The observations in the 4 space views have been analysed over the lifetime of AIRS to derive a time-dependent correction.
  • The overall uncertainty of the calibration is reduced by a factor of ~2 (at 220K) in most bands.
  • Tom will prepare some slides for for inclusion as part of the planned presentation on the "IRRefUTable Report"

A.GIR.20170627.1: Tim Hewison to set up web meeting to discuss IASI-A/B double differences and migration at end 2017.

A.GIR.20170627.2: Scott Hu (CMA) to nominate point of contact to contribute IASI-A/B double differences against FY-2/4.

A.GIR.20170627.3: Tim Hewison (EUMETSAT) to consider inclusion of SLSTR results in IASI-A/B double difference analysis.

A.GIR.20170627.4: Tim Hewison (EUMETSAT) to add CMA, JMA, NOAA and KMA contributors as authors to Traceability Report and export to ZoHo and circulate.
Topic revision: r13 - 11 Jul 2017, ManikBali
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