1EUM/RSP/VWG/16/ Tim Hewison Tom Stone Manik Bali Selecting and Migrating GSICS Inter-Calibration Reference Instruments

2EUM/RSP/VWG/16/ Introduction-GSICS References GSICS Reference Instruments are at the Center of instrument Monitoring and Classical GSICS Product Generation. Stability and accuracy (over time) of reference instrument are vital parameters for ensuring good quality of GSICS inter-calibration monitoring. AIRS IASI MODIS GSICS Aims [Ref: WMO website ]WMO website Monitoring instrument performances, Operational inter-calibration of satellite instruments- GSICS Products Operational inter-calibration of satellite instruments- GSICS Products Tying the measurements to absolute references and standards, and recalibration of archived data Slide from Manik Bali

3EUM/RSP/VWG/16/ Overview 1.Proposed Reference Instrument Selection Scheme 2.Prime GSICS Corrections (not for presentation, just for CGMS Report) Merging results from multiple references Anchor Reference Concept 3.GSICS Infrared Reference Sensor Traceability and Uncertainty Report 4.Choice of Reference for Microwave Imagers/Sounders 5.Requirements for lunar reference models (not for CGMS Report) 6.Conclusions

4EUM/RSP/VWG/16/ Proposed GSICS reference Instrument selection process 1.The instrument and Channels agency wishes to monitor 2.The method/s they would employ to monitor (e.g. single or blended references, use transfer target, stability criterion) 3.May consider scoring proposed by Hewison and Reference Expectations gathered by GSICS Survey 4.Demonstrated use of the instrument by member agencies and users for instrument monitoring 5.Comparison of Instrument design specification ( Pre-launch testing) with In-orbit behavior 6.May consider if in-orbit status of key parameters of Candidate Ref instrument are monitored and available to users ( such as ICVS) 7.Take Info ( global coverage, eq. cross time etc) related to instrument available (e.g. OSCAR) Process of Selection to be carried out within sub group. Slide from Manik Bali

5EUM/RSP/VWG/16/ Reference Instrument Selection Criteria 1. Basic requirements are essential properties for each product: Threshold (may be binary) Is it available for the date in question? (Essential for SNO, not for PICS) Does it cover at least part of the spectral range of monitored instrument? Does it generate sufficient collocations? Is its calibration sufficiently stable? Can it transfer the calibration to other Reference sensors? Is it routinely monitored against other Reference sensors? Is the full supporting documentation published? 2. Additional desirable requirements – for all products in class: -reflect reduced uncertainties in inter-calibration, -up to a saturation point, represented by goal: Does it cover the full spectral range? At sufficiently high spectral resolution?

6EUM/RSP/VWG/16/ Proposed Anchor Reference Selection Scheme Review instrument performance parameters critical to role as inter-calibration reference For each parameter: Define Threshold requirement (min) - below which the instrument is not useful Define Goal (max) - above which no further uncertainty reduction Define Weighting - Based on coverage/contribution to uncertainty

7EUM/RSP/VWG/16/ Proposed Anchor Reference Selection Scoring Consider all monitored instruments in Class e.g. All GEO imagers in 2014 Date Range Reference must operate this year Ideally cover full life of all instruments Spectral Range Must cover centre of all GEO imager channels in each band Ideally cover full spectral band of all GEO imager channels in each band Weighting proportional to # GEO imager channels Other important parameters: Geolocation accuracy Radiometric stability Uncertainty from SBAF Absolute calibration accuracy Documented Traceability Chain (Scored 0-6)

8EUM/RSP/VWG/16/ Draft Scores for GSICS GEO-LEO IR NRTC

9EUM/RSP/VWG/16/ Overview 1.Proposed Reference Instrument Selection Scheme 2.Prime GSICS Corrections (not for presentation, just for CGMS Report) Merging results from multiple references Anchor Reference Concept 3.GSICS Infrared Reference Sensor Traceability and Uncertainty Report 4.Choice of Reference for Microwave Imagers/Sounders 5.Requirements for lunar reference models (not for CGMS Report) 6.Conclusions

10EUM/RSP/VWG/16/ Introducing Prime GSICS Corrections Define one Anchor GSICS Reference for each spectral band/application by consensus agreement within GSICS to provide reference standard datasets [QA4EO] Use others as Transfer References Blend corrections from all references after modifying Corrections to Anchor GSICS Reference Ensures long-term continuity without calibration jumps Ensures Traceability back to single Anchor Reference Simplifies users’ implementation

11EUM/RSP/VWG/16/ Correcting the Corrections & Blending References Reference-1 (Anchor) Monitored Instrument GSICS Correction, g 1 Mon  1 Reference-2 (Transfer) GSICS Correction, g 2 Mon  2 Mon  1 Delta Correction, g 1/2 2  1 Derived by GSICS Applied by User Corrected Correction, g 2,1/2 Mon  2  1 Prime GSICS Correction, g 0 Mon  1 - g̅ +

12EUM/RSP/VWG/16/ Users’ Application of Prime GSICS Correction Monitored Instrument Prime GSICS Correction, g 0 Mon  1 Mon  Ref1

13EUM/RSP/VWG/16/ Overview 1.Proposed Reference Instrument Selection Scheme 2.Prime GSICS Corrections (not for presentation, just for CGMS Report) Merging results from multiple references Anchor Reference Concept 3.GSICS Infrared Reference Sensor Traceability and Uncertainty Report 4.Choice of Reference for Microwave Imagers/Sounders 5.Requirements for lunar reference models (not for CGMS Report) 6.Conclusions

14EUM/RSP/VWG/16/ IR Reference Sensor Traceability & Uncertainty Report Introduction- Hewison Aims To support the choice of reference instruments for GSICS and Metop-A/IASI as Anchor To provide traceability between reference instruments (IASI, AIRS, CrIS) By consolidating pre-launch test results and various in-flight comparisons To seek consensus on the uncertainties in the absolute calibration of the reference sensors Limitations No new results, just expressing results of existing comparisons in a common way, reformatting where necessary, to allow easy comparisons. Error Budget & Traceability Focus on Radiometric and spectral calibration AIRS- Pagano + Wang? IASI - Jouget + Jacquette CrIS- Tobin + ? Inter-comparisons Introduction: Pros and Cons of each method - Wang Polar SNOs - Jouglet, Tobin, Wang Tandem SNOs (AIRS+CrIS) – Tobin Quasi-SNOs- Jouglet GEO-LEO Double Differencing- Hewison +? NWP Double-Differencing- Wu +? Regional Averages (“Massive Means”)- ? Aircraft Double-Differences- Tobin +? Reference other methods e.g. Dome-C Conclusions- All Target Time-scale: Web Meeting: - Agree structure, authors, templates Web Meeting: - Review Draft Error Budgets GRWG Meeting - Discuss presentation of results

15EUM/RSP/VWG/16/ IR Reference Sensor Inter-Comparisons Re-binning results of existing comparisons to make them comparable: Biases with respect to MetopA/IASI With standard uncertainties (k=1) At full spectral resolution - in CrIS channel-space – or in 10cm -1 bins within AIRS bands Averaged over specific spectral bands Or average results over broad-band channels With specific SRFs - rectangular? Converted into Brightness Temperatures For specific radiance scenes - e.g. 200K, 220K, 240K, 260K, 280K, 300K For all viewing angles and/or for specific ranges - e.g. nadir±10°? - not possible for QSNOs Need to check for scan-angle dependence - which methods can do this? Over specific period - e.g. at least 1 year Common 3 year period from IASI-B operational start to present ( / ) Noting any significant changes with time And Trends

16EUM/RSP/VWG/16/ Overview 1.Proposed Reference Instrument Selection Scheme 2.Prime GSICS Corrections (not for presentation, just for CGMS Report) Merging results from multiple references Anchor Reference Concept 3.GSICS Infrared Reference Sensor Traceability and Uncertainty Report 4.Choice of Reference for Microwave Imagers/Sounders 5.Requirements for lunar reference models (not for CGMS Report) 6.Conclusions

17EUM/RSP/VWG/16/ References for Microwave Imagers/Sounders Microwave Sub-Group currently addressing Selection of appropriate reference instruments expected to follow a similar procedure Different spectral bands may use different instruments for example temperature-sounding channels in the 60 GHz oxygen band, humidity-sounding channels in the 183 GHz band and microwave window channels. Potential use of RTM as reference Concerns about traceability – spectroscopy + background Is this GSICS? – Inter-Calibration? Expertise?

18EUM/RSP/VWG/16/ Overview 1.Proposed Reference Instrument Selection Scheme 2.Prime GSICS Corrections (not for presentation, just for CGMS Report) Merging results from multiple references Anchor Reference Concept 3.GSICS Infrared Reference Sensor Traceability and Uncertainty Report 4.Choice of Reference for Microwave Imagers/Sounders 5.Requirements for lunar reference models (not for CGMS Report) - Tom 6.Conclusions

19EUM/RSP/VWG/16/ Requirements for an Absolute Lunar Calibration Reference 1. Developing an Absolute Lunar Reference -The Moon potentially can be an absolute reference with accuracy ≤1% (k=2) this is beyond current capabilities limitations are with the current USGS ROLO lunar model, not the Moon -To meet the objective of ≤1% (k=2) absolute accuracy for a lunar radiometric reference requires collecting a new measurement database -GSICS has developed a potential approach and tentative set of requirements : A) Requirements for Ground-based Measurements  Purpose: a detailed characterisation of the Moon’s brightness variations  Spatial coverage : spans ~60% of the lunar surface lunar librations (coverage requires a minimum of 3 years of observations)  A practical limit on the lunar phases : to observe at night (phase angles up to 90° before and after Full Moon)  Spectral coverage : to correct the lunar measurements to TOA values  contemporaneous atmospheric transparency measurements to accommodate differences in SRFs of different sensors requirement : 2 ‒ 3 nm resolution with 1 ‒ 2 nm sampling

20EUM/RSP/VWG/16/ Requirements for an Absolute Lunar Calibration Reference B) Requirements for Above-atmosphere Measurements  Purpose: to scale and validate the ground-based measurements  Potentially can extend the phase range e.g. 135° makes lunar calibration available for three weeks of each month  Spectral measurements : full coverage needed, to capture the solar spectral structure (<~700 nm) for longer wavelengths, may be in discrete bands (for mission constraints) minimum specifications : 8 nm resolution and 4 nm sampling C) Formulation of the Lunar Reference Standard  The Moon’s brightness is governed by : the surface reflectance phase function the solar spectral irradiance at the location of the Moon  And, for the lunar irradiance quantity : the hemispheres of the Moon the distance between the Moon and the observer.  The formulaic expression for lunar disk reflectance is developed empirically analytic functions or a parametric form, as appropriate coefficients developed by fitting the ground-based measurements  Estimated contribution to the overall uncertainty in the reference standard : ≤0.5% (k=2) : due only to model formulation and fitting the basis dataset

21EUM/RSP/VWG/16/ Requirements for an Absolute Lunar Calibration Reference 2. Capabilities enabled by an absolute lunar reference standard ‒ Provides consistent inter-calibration using the same reference no requirement for near-simultaneous observations e.g. meteorological imagers, have acquired many Moon observations improved calibration accuracy can decrease the time needed to retrieve the signals of climate change from the background of natural variability (e.g. CLARREO mission concept) ‒ Potential to bridge a gap in an otherwise continuous set of observations the same stable reference can be observed before and after the break 3. Impact on Requirements for space-based sensors ‒ Given a lunar reference standard with absolute accuracy ≤1.0% (k=2), the calibration requirements for future solar band sensors can be set to a similar level ‒ The corollary requirement is that instruments must observe the Moon recommend acquiring multiple observations, to reduce the scatter recommend observing the Moon regularly (at least monthly) ‒ Recommend acquiring a baseline set of lunar observations to evaluate transfer-to-orbit calibration changes to establish a benchmark for temporal trending

22EUM/RSP/VWG/16/ Requirements for an Absolute Lunar Calibration Reference 5. Conclusions The availability of a high-accuracy lunar reference standard: significant impact on Earth observation datasets acquired from space (by way of improved consistency and inter-operability across sensors and platforms) ‒ provide benefits to climate monitoring programs & satellite operating agencies worldwide Requirements ‒ collecting a new, high-accuracy set of characterization measurements of the Moon ‒ redeveloping the lunar reference using this improved dataset 4. Actions and Recommendations (1)Satellite instrument operators should establish requirements to observe the Moon with VIS/NIR channel sensors. (2)Satellite operating agencies should support proposals and programs to acquire high-accuracy characterization measurements of the Moon, to develop a new, high accuracy, SI-traceable lunar reference standard for reflected solar wavelengths. (3)Long-term continuity of absolute solar spectral irradiance measurement with SI- traceable accuracy should be ensured.

23EUM/RSP/VWG/16/ Overview 1.Proposed Reference Instrument Selection Scheme 2.Prime GSICS Corrections (not for presentation, just for CGMS Report) Merging results from multiple references Anchor Reference Concept 3.GSICS Infrared Reference Sensor Traceability and Uncertainty Report 4.Choice of Reference for Microwave Imagers/Sounders 5.Requirements for lunar reference models (not for CGMS Report) 6.Conclusions

24EUM/RSP/VWG/16/ Conclusions Prime Corrections merge results from multiple references Correcting all to be consistent with one Anchor Reference Based on series of double-differences wrt monitored instrument Need to progress to Demo mode! Selection of Anchor reference based on coverage/performance According to uncertainty contributions Inter-comparisons of different reference instruments GSICS IR Reference Sensor Traceability & Uncertainty Report Error Budgets, Traceability and Inter-Comparisons Requirements for lunar reference models Recommendation to CGMS to obtain the observations necessary to improve the lunar irradiance modeling capability to the point where it can be used as an absolute calibration reference for channels in the VIS/NIR with an uncertainty of<1% (k=2)

25EUM/RSP/VWG/16/ Thank You!