Strategy for calibration references Special Issue of the IEEE TGRS on “Inter-Calibration of Satellite Instruments”: Special Issue of the IEEE TGRS on “Inter-Calibration of Satellite Instruments”: 17 January 2019 Strategy for calibration references Tim Hewison (EUMETSAT) (GRWG Chair)

Overview Update on Prime GSICS Corrections For information How to select inter-calibration reference instruments Improving the Moon As a calibration reference A case for international collaboration Recommendation needed!

Overview Update on Prime GSICS Corrections For information How to select inter-calibration reference instruments Improving the Moon As a calibration reference A case for international collaboration Recommendation needed!

New Prime GSICS Corrections Define one Primary GSICS Reference For each spectral band/application By consensus agreement within GSICS Use others as Transfer References Blend corrections from all references After modifying Corrections to Primary GSICS Reference Ensures long-term continuity Without calibration jumps Ensures Traceability back to single Primary Reference Simplifies users’ implementation Could also blend multiple methods?

Correcting the Corrections and Blending References Reference-1 (Primary) Monitored Instrument Reference-2 (Secondary) GSICS Correction, g1 Mon1 GSICS Correction, g2 Mon2 - Derived by GSICS Delta Correction, g1/2 21 + Modified Correction, g2,1/2 Mon 21 g̅ Prime GSICS Correction, g0 Mon1 MonRef1 Applied by User

Users’ Application of Prime GSICS Correction Monitored Instrument Prime GSICS Correction, g0 Mon1 MonRef1

Overview Update on Prime GSICS Corrections For information How to select inter-calibration reference instruments Improving the Moon As a calibration reference A case for international collaboration Recommendation needed!

Reference Instrument Selection/Migration GSICS products need an inter-calibration reference Inter-calibration  Reference is one instrument Other instruments may be used as transfer references We need a way to select the reference From a list of candidates First question should be: “Is it suitable at all?” Does it meet minimum threshold requirements (availability, coverage, ...) Started asking “How good is it as a Reference?” Impact on overall uncertainty Score scheme

Example for SEVIRI-IASI IR Scoring Scheme for GSICS Re-Analysis Correction for SEVIRI IR Channels   Threshold Saturation MetopA/IASI Unit Min Max Weight OK? Perfect Score Date Range Year 2013 2006 2030 90 2007 2020 Pass 54% 48.8 Geographic Coverage: Lat deg -10 10 -90 2 100% 2.0 Geographic Coverage: Lon -180 180 Dynamic Range K 270 300 330 5 310 87% 4.3 Spectral Range cm-1 746 2564 650 2800 645 2760 98% 9.8 Geometric Range: VZA 15 0.5 55 61% 1.2 Geometric Range: VAA 0.0 Geometric Range: SZA Geometric Range: SAA Geometric Range: Pol Diurnal Coverage hr 9 12 20 7.8 11.2 28% 5.6 Field of View km 3 1 1.0 Number of obs/day /d Number of Collocations 10000 30000 5.0 Geolocation accuracy 0.1 3.3 3% 0.3 Polarisation knowledge Radiometric Stability K/yr 0.001 0.05 2% 0.2 Orbital Stability hr/yr Radiometric Noise 0.15 67% 0.7 Uncertainty from SBAF 0.01 0.008 20.0 Spectral Resolution 100 0.25 Spectral Stability cm-1/yr 2E-06 SBAF Uncertainty 1% Absolute Calibration Acc Inter-channel calibration Data Availability Documentation Community adoption Traceability Fail Total 200.0 96% 51% 101.1 Example for SEVIRI-IASI IR OneDrive Spreadsheet All values for illustration only And subject to change Some variables more important for different inter-cal products Timeliness important for NRTC Date range critical for Archive Re-Calibration Assumed time-stamp is correct! Scheme needs road testing with other References

Expanding WMO OSCAR Capabilities Observing Systems Capability Analysis and Review Tool Adding Landing Pages with links to: Instrument Specifications, Calibration Events, Data Outages, Instrument Monitoring WMO expanding OSCAR automatically assess instruments’ capability to address requirements Based on pre-defined Expert Rules Could be used to assess GSICS References Action: Manik to interact with Jérôme to push forward the development of the expert system as a tool to select inter-calibration reference instruments 

Instrument view GSICS - New Delhi- OSCAR 16-20/03/2015

Overview Update on Prime GSICS Corrections For information How to select inter-calibration reference instruments Improving the Moon As a calibration reference A case for international collaboration Recommendation needed!

Lunar Calibration Workshop Organised by EUMETSAT in collaboration with USGS, CNES, NASA Almost 30 people from 14 different agencies and departments attending (physically or remotely)  GSICS / CEOS-IVOS All participants used GSICS Implementation of ROLO model (GIRO) developed at EUMETSAT in collaboration with T. Stone (USGS) To develop inter-calibration algorithm, need accurate oversampling factors  difficulty encountered by all participants Major outcomes: the calibration community agreed the GIRO to be the international reference for lunar calibration, traceable to the ROLO model from USGS Establishment of a Lunar Observation Database Recommend investigating possible funding to establish infrastructure to traceable lunar observations Participants in the Lunar Calibration Workshop Hosted at EUMETSAT, 1-4 Dec 2014 A GIRO usage policy and a data policy will be defined in collaboration with the participants USGS expected to have a new version of the ROLO by the end of 2015  updated GIRO by mid-2016 All participants agreed about the need to organise another Lunar Calibration Workshop (~1 year time)

Number of Obs (GSICS dataset) Instruments Team Satellite Sensor G/L Dates Number of Obs (GSICS dataset) Phase angle range (°) CMA FY-3C MERSI LEO 2013-2014 9 [43 57] FY-2D VISSR GEO 2007-2014 FY-2E 2010-2014 FY-2F 2012-2014 JMA MTSAT-2 IMAGER 2010-2013 62 [-138,147] GMS5 1995-2003 50 [-94,96] Himawari-8 AHI 2014- - EUMETSAT MSG1 SEVIRI 2003-2014 380/43 [-150,152] MSG2 2006-2014 312/54 [-147,150] MSG3 45/7 [-144,143] MET7 MVIRI 1998-2014 128 [-147,144] CNES Pleiades-1A PHR 2012 10 [+/-40] Pleiades-1B NASA-MODIS Terra MODIS 2000-2014 136 [54,56] Aqua 2002-2014 117 [-54,-56] NASA-VIIRS NPP VIIRS 20 [50,52] NASA-OBPG SeaStar SeaWiFS 1997-2010 204 (<10 , [27-66]) NASA/USGS Landsat-8 OLI 3 [-7] NASA OCO-2 OCO 2014 NOAA-STAR 2011-2014 19 [-52,-50] NOAA GOES-10 1998-2006 33 [-66, 81] GOES-11 2006-2007 [-62, 57] GOES-12 2003-2010 49 [-83, 66] GOES-13 2006 11 GOES-15 2012-2013 28 [-52, 69] VITO Proba-V VGT-P 25 KMA COMS MI 60 AIST ASTER 1999-2014 1 -27.7 ISRO OceanSat2 OCM-2 2009-2014 2 INSAT-3D Instruments with lunar observation capabilities, with the minimum number of Moon observations provided to the GSICS Lunar Observation Dataset (GLOD) - more observations may be available.

Examples of Moon observations from participating instruments

According to OSCAR (WMO) Courtesy B. Fougnie, CNES LEO (CWL) GEO (band) Landsat-8 According to OSCAR (WMO)

Courtesy B. Fougnie, CNES LEO GEO Landsat-8

Courtesy B. Fougnie, CNES LEO GEO Landsat-8

Improving the Moon (as a reference) Where we are: GSICS Implementation of ROLO (“GIRO”) v1.0.0 now available, validated against ROLO Starting to compile GSICS Lunar Observations Database (“GLOD”) Already found significant dependencies in relative biases of Observed-GIRO irradiances But still good enough to inter-calibrate 0.6m band to <1% uncertainty (NIR not so good) Absolute calibration using GIRO limited to 5-10% by original ROLO dataset Short-term plan: Develop inter-calibration algorithm Integrate results with DCCs in new GSICS products Continue to expand GSICS Lunar Observations Database (“GLOD”) Form community consensus on absolute scale of GIRO Long-term plan: Tie GIRO to SI-traceable standards Ideally through long-term campaign of new hyperspectral lunar observations

Proposal for activities to address inter-calibration using the Moon In EUMETSAT’s proposal, points to be addressed: Estimating the over-sampling factor Drift correction Estimation of the SBAFs from GIRO and verification of the results. Establishing an absolute scale for lunar calibration Medium and long term activities on lunar calibration

ROLO/GIRO and absolute calibration KNOWN DEFICIENCIES OF THE CURRENT REFERENCE SI traceability Absolute scale uncertainty (5 – 10 % uncertainty in absolute irradiance scale) Residual geometry dependencies Multi-band spectral coverage ESTABLISHING THE REQUIREMENTS Defining potential improvements and requirements on user applications Independent method to verify that operational visible calibration meets requirements  Support climate applications and past instruments (e.g. no onboard calibration available) GOAL Getting absolute uncertainties to under ~1% Surface stability + predictability of the Moon’s brightness = lunar reflectance model valid for all times Level of accuracy of 0.5% is achievable WHAT IS NEEDED? Need for a new lunar measurement program (= many years of observations, to characterize the variations of the lunar brightness with phase and librations) Minimum 3 years to capture the libration dependence within the bounds of its relative effect (ROLO operated for more than 8 years) Traceable high-spectral resolution observations over several years with specific measurements to validate the atmospheric correction. FUNDING: Currently under investigation (inter-agency [international] collaboration?)

E. Medium and long term activities on lunar calibration Investigate the possibility to participate to an international consortium to fund dedicated measurement campaigns. Review planned activities in this area: CMA: Obtained funding for new ground-based observations from CAS CNES? ESA: interest in contributing but no existing mechanism for such an international funding. Further investigations needed. EUMETSAT: no existing mechanism for international funding but possibility still under investigation. Science Working Group defines users requirements. ISRO? IMD? JMA: no possibility for funding KMA? NASA: Proposed ARCSTONE mission for Earth Venture funding NOAA? CEOS/IVOS members: AIST, JAXA, KIOST, VITO?

Conclusions Advice of CEOS-WGCV for GSICS: Requirements: Develop inter-calibration using current GIRO as soon as possible Support SI-traceable lunar observations to tie ROLO to absolute scale Encourage independent reproduction of ROLO observations Requirements: System suitable for operational application (source code) Globally accessible common lunar irradiance model Recommendation is sought from GSICS/CGMS: How to establish international cooperation to establish, operate and process A campaign of new lunar observations over full range of conditions (>3yr) Covering full reflected solar band at high spectral resolution (hyperspectral) Directly traceable to SI standards

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