GRWG IR Sub-Group Web Meeting 2017-12-14
GSICS Web Meeting on Reference Migration from IASI-A to IASI-B
- Dorothée Coppens (EUMETSAT) - Delaying the roll-out of non-linearity changes to IASI-A
- Double differencing of IASI-A/B against geostationary imagers' IR Channels
- Igor Tomazic (EUMETSAT) – Double differencing of IASI-A/B against SLSTR
- Elsa Jacquette (CNES) - IASI-A/B direct and indirect comparisons
- All - Discussion on strategy for migrating GSICS products from IASI-A to IASI-B
- All – Implications for the IR Reference Uncertainty Traceability Report (“IRRefUTable”)
- Dave Smith (RAL) - SLSTR traceability chain
Other topics - may be defered until annual meeting
- Tim Trent (U Leicester) - Alternative Regression algorithms for inter-calibration (postponed to 2018 GRWG meeting)
- Chengli Qi (CMA) - Radiance Uncertainly estimate for HIRAS (postponed to 2018 GRWG meeting)
- Hui Xu (NOAA) - Using PCA regression to fill up spectral gap (postponed to 2018 GRWG meeting)
- Likun Wang (NOAA) - Fast and accurate collocation package of CrIS with GOES16 or other geostationary imager (postponed to 2018 GRWG meeting)
This web meeting of IR Sub-Group focused on the migration of the inter-calibration reference from the IASI on Metop-A to Metop-B, following the action raised at our last web meeting in June 2017
It reviewed the results of several analyses of the relative performance of these reference instruments – for example, from GEO-LEO Double Differencing - particularly since the change to IASI-B onboard processing in August 2017.
A strategy to merge multiple references for NRT product and the implications for the IR Reference Uncertainty Traceability Report (“IRRefUTable”) were also discussed.
Guest Chair: Tim Hewison
CMA: Hanlie Xu
CNES: Elsa Jacquette
EUMETSAT: Tim Hewison, Alessandro Burini, Sebastien Wagner, Igor Tomazic, Viju John, Dorothée Coppens (PT)
JMA: Masaya Takahashi and Yusuke Yogo
KMA: Dohyeong Kim, Minju Gu, Eunkyu Kim and Hyeji Yang
NOAA: Fangfang Yu, Likun Wang, Manik Bali
RAL: Dave Smith
: Tim Trent
Dorothée Coppens reported that unexpected results had been found since the roll-out of the non-linear correction to Metop-B/IASI. These are not fully understood, and are currently under review. A decision will be made by an ISSWG Task Force in mid-March 2018 to whether to roll-out the correctoin to Metop-A/IASI. Previously this was planned to take place in Feb 2018, but has now been delayed until at least Sept 2018, after which the Metop-A orbit will begin to drift more rapidly - and may be cancelled altogether. The Task Force would be happy to consider a recommendation from GSICS, which Tim will formulate.
- Mean DD is larger in long WL channels and for colder scenes.
- IASI-B change caused DD to jump from ~0.04K colder than IASI-A to ~0.04K warmer (for standard scenes)
- Longer WL channels showed the jumping pattern from minus to plus around 0.1K, larger jump at cold scenes after IASI non-line correction
- After update of ABI scan mirror emis LUTs, WV channles are affected (ABI-CrIS)
- For the anlaysis of DD, collocation, scan angle, and so on should be taken care.
- Before scan mrrr emm, there is diurnal variation…. ---> thus update the values
- -- AHI will be considered the update of the scann mrr emissivity
- FY-4A channel 8 to 14
- Show FY-2G DD : after Aug 2017 jump around 0.05 to 0.1K
- Check the Hyperspectral collocation… for the WV channel large bias
- Recommend not mean Temp but std temp
- SLSTR : with IASI less than 0.1 K difference bewteen 220 and 280K
- DD is ~0.05K function of SNO event, scene Temp similarly MSG/SEVIRI
- S9 : det0 and det1 -- SRF slightly different, but small
IR Reference Sensor Traceability & Uncertainty Report
- The effects of IASI-B non-lin correction are depend on temp and WN (larger at cold temp, and longer WL)
- A/B direct comparison: good except CO2, O3 band
- Befere : negavtive --> after … flat pattern but small residuals due to A non-linearty
- IASI-A non linearity table will be update : Feb 2019
- 1st TF team meeting of ISSWG will be held in mid March 2018 --> Outputs will be reported at GSICS annual meeting
- the change IASI-A, the inter-calibration with IASI-B and CrIS will be worse, and the update is postponed
- IASI-A/B DD is no time dependent
- JMA (Masaya), CMA(Hanlie?), NOAA(??), KMA(Dohy) will contribute the IASI-A/B DD analysis…
Possible strategy for migrating GSICS products from IASI-A to IASI-B
Previously, Tim had proposed the concept of the Prime GSICS Corrections, whereby comparisons with different reference instruments are adjusted by delta corrections, based on double-differences. This is still felt to be a good approach for generating FCDRs.
But adoption of the idea in Near Real-Time Corrections has been slow, so a simpler alternative is now proposed:
One idea is to first perform a comparison of the results with all available references.
This could be used to establish a consensus reference, as a weighted average of the results from all the references that are within the consensus uncertainty.
Of course, this would result in jumps in the time series
– but they would be within the consensus uncertainty, which estimates the absolute uncertainty on the merged GSICS corrections.
Dave: SLSTR calibration
Of course, this may be large than the uncertainty derived using a single reference, and this increase may be critical for some applications.
And we need to establish some values before deciding whether to adopt this approach.
Tim will formulate the questionnaire for non-linearity of IASI-A to provide TF team of ISSWG in March 2018.
- Non-blackness and temp gradiaents in flight made different between measured and actual BT