EUMETSAT water vapour imagery products from new generation satellites: development and validation strategy
L. Spezzi*, P. Watts, B. Fougnie, J. Chimot, E. Obligis, B. Bojkov
1 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) Water Vapour Product map (missions & products)
EUMETSAT instrumentation: IR and MW sounders, MW imagers, VIS/IR imagers, UV/VIS spectrometers
Operational In development Possible Planned only Not yet committed/under study Not Applicable (not yet in plan → room for @EUMETSAT @SAFs @EUMETSAT @EUMETSAT improvement) and/or SAFs and/or SAFs
E.g. talk by Sküchler: “Total water vapor column from Sentinel-5P derived by the AMC-DOAS method”
Instr./ Metop MSG Sentinel 3 Metop-SG MTG AMSU IASI S5 S4 AVHRR IASI MWR MWI ICI MWS IRS Product MHS SEVIRI OLCI SLSTR VII 3MI NG UVNS FCI UVN Total Colum Water Vapour (clear-sky) Layer Precipitable Water 1=surface to 850hPa 2=850 to 500 hPa 3=500 hPa to TOA Humidity profile
2004 to present 2016 2022+ Time to present Talk by T. August: ‘’IASI retrieval and validation activities at EUMETSAT: Recent updates’’ 2 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) EUMETSAT sensors for water vapour imagery High spatial resolution
Main types of sensors providing imaging measurements for water vapour retrieval Current: • Multispectral Pushbroom and Dual-view radiometer: →Sentinel-3/OLCI and SLSTR ECMWF does not always S3/OLCI (300m) • Geostationary multi-spectral imagers: resolve all features →MSG/SEVIRI Future: • Geostationary multi-spectral imagers: →MTG/FCI • Polar multi-spectral imagers: →EPS-SG/METimage • Multi-directional Polarimeter: • WV concentration in the boundary layer is an indicator of →EPS-SG/3MI mesoscale developments (scale ~4km), e.g. convection, etc.
• Detection of upper troposphere WV wind fields in the vicinity of storms to track troughs, jet maxima, divergent regions, etc.
• Identification of onset or end of severe weather (1 to 2.5 km)
3 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) Sentinel 3 - OLCI & SLSTR: ENVISAT optical imagery legacy with technology improvements 2 optical instruments with medium spectral resolution & high spatial resolution
OLCI: Push-broom imaging SLSTR: Conical scanning imaging radiometer spectrometer • Along-track dual view (nadir & oblique • 12 degrees westward tilt, to backward) minimize Sun glint • Swaths 1420km (nadir) & 750km (oblique) • Swath 1250 km • Pixel size nadir: 500m (VIS-NIR-SWIR), 1km • Pixel size@Nadir: 300m (fine), (TIR) 1.2km (reduced)
Additional channels from MERIS / AATSR 4 EUMETSAT Water Vapor Imagery2 sameproducts channels @ G-VAP with Meeting different (Madrid, dynamic 13/14 June range 2019) Sentinel-3 – 3 TCWV products from complementary instruments
TCWV – OLCI (Near-InfraRed) Spectral Earth GmbH • Baseline MERIS-like, available over all surfaces (J. Fischer, R. Preusker) • 8%-13% wet bias over land confirmed though validation with AERONET, ARN, GNSS, and radiosondes. Larger over seas. • Evolutions in progress since July 2018
▪ Updated H2O line absorption (HI 2016) + continuum ▪ Better sea surface BRDF model (Cox & Munk 54 + shadow)
▪ Use of 5 OLCI H2O absorption channels (from 0.865 to 1.020 µm) + spectral smile correction ▪ Optimal Estimation inversion with uncertainty propagation. Updated state vector over sea (wind + aerosols)
TCWV – SLSTR (Thermal InfraRed + dual-view) - Just initiated • Baseline AIRWAVE Casadio, et al., 2016, 2018 Talk by L. Castelli: AIRWAVE v2 TCWV from ATSR series: performance improvements • Dual-view (nadir & oblique) – Linear solving equation using the 2 TIR channels (10.8 & 12 µm) • Demonstrated for 20-year (A)ATSR instrument series day-night over water surfaces. Global bias over sea: • 0.02 ± 4.79 kg.m−2 (SSM/I) • 0.19 ± 6.12 kg.m−2 (ARSA)
5 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) MSG, EPS-SG & MTG VIS/IR imagers: water vapour capabilities
λC EPS-SG MTG MSG Comments (µm) METimage FCI SEVIRI
0.44 Yes Yes NO Windows channel (aerosol scattering) 0.55 Yes Yes NO Window channel (aerosol scattering) LAND LAND 0.67 Yes Yes Yes Window channel (surface reflection) LAND
0.75 Yes NO NO O2 continuum
0.76 Yes NO NO O2 A-band (cloud top pressure) 0.86 Yes Yes Yes Window channel (surface reflection) 0.91 Yes Yes NO H O absorption channel 2 Sunglint SEA 1.24 Yes NO NO Windows channel (surface SEA reflection)
1.37 Yes Yes NO H2O absorption channel 1.63 Yes Yes Yes Windows channel 2.25 Yes Yes NO Windows channel 3.74 Yes NO NO Windows channel SEVIRI 6.7 3.90 Yes Yes Yes Windows channel 4.05 Yes NO NO Windows channel
6.72 Yes Yes Yes H2O absorption channel
7.32 Yes Yes Yes H2O absorption channel 8.54 Yes Yes Yes Windows channel
9.66 NO Yes Yes O3 absorption band ~11 Yes Yes Yes Window channel ~12 Yes Yes Yes Window channel
~13 Yes Yes Yes CO2 absorption band
6 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) MSG, EPS-SG & MTG VIS/IR imagers: spatial resolution
Spatial resolution @ Nadir (km) VIS IR SEVIRI 3 3 FCI 1 2 METimage 0.5 0.5
7 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) MSG, EPS-SG & MTG water vapour retrievals: a 1Dvar approach
Elements of 1Dvar in water vapour retrieval:
• Measurement vector: y = VIS, IR or VIS/IR measurement up to 20 channels
• Measurement error covariance matrix (diagonal, i.e., errors in different channels are uncorrelated):
Sy = channel noise, inhomogeneity noise, channel co-registration error, biases, RTM errors
• State vector (full profile or principal components): x = Q(p), T(p), surface BRDF/emissivity, surface temperature, AOD
• Forward RT model: F(x) = RTTOV 12.1+
• Prior state vector:
xa = ECMWF forecast, auxiliary land databases + Cox & Munk over ocean, CAMS
• Prior error covariance matrix:
Sa = ECMWF/Ensemble Long-Window data assimilation, ~10% BRDF/emissivity uncertainty over land & estimated forecast wind speed error over ocean, CAMS uncertainty
8 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) EPS-SG/3MI: water vapour capabilities
2D Push-broom radiometer (2200 km swath, 4 km pixel at nadir)
3MI channels Provides images of the Earth TOA outgoing radiance using (4km@Nadir): 410-P ± 10 nm - Multi-view (10 to 14 views; angular sampling in the order of 10°) - Multi-channel (12 channels from 0.41 to 2.13µm, including the 0.9µm absorption channel) 443-P ± 10 nm - Multi-polarisation (9 channels with -60°, 0°, +60° polarisers) 490-P ± 10 nm
555-P ± 10 nm CCD VNIR VNIR Detector Optical Head 670-P ± 10 nm (509x509 pixels) 763 ± 5 nm
765 ± 20 nm
865-P ± 20 nm
910 ± 10 nm Filter wheel
1370-P ± 20 nm
1650-P ± 20 nm CMOS SWIR SWIR Detector Optical Head 2130-P ± 20 nm (255x499 pixels)
9 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) EPS-SG 3MI water vapour product
Available information: band 865 (braod band) and band 910 (narrow band centred on absorption) - Integrated WV content: approach from Vesperini et al. (1999), POLDER heritage
Description of the algorithm steps: • Clear sky pixel only: cloud fraction from METimage < 0.05 (TBC) • tH2O = Mtoa(910) / Mtoa(865) where 910 is the absorption band, and 865 the baseline
Ocean (sunglint only): • if tH2O < threshold then
uH2O = [ Cocean,4 x ln²(tH2O) ] / airmass • endif polynomial :
uH2O = [ Cocean,3 x ln²(tH2O) + Cocean,2 x ln(tH2O) + Cocean,1 ] / airmass
Land: For clear sky pixel → additional surface term based on the ratio 865/765 • if tH2O < threshold then
• uH2O = [ Cland,4 x ln²(tH2O) + Cland,5 x ln(865/765) ] / airmass
• endif polynomial :
• uH2O = [ Cland,3 x ln²(tH2O) + Cland,2 x ln(tH2O) + Cland,1 + Cland,5 x ln(865/765) ] / airmass
Estimated for every valid of the 14 views → calculation of the mean value + STDDEV
Validation: Against radiosondes and ECMWF analysis
10 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) Needs for Operational Use – General Requirements
EUMETSAT provides operational atmospheric products, which implies: • Reliability: more than 99% - 24/7 • Timeliness: Near Real Time dissemination from sensing time ✓100 to 150 minutes for LEO ✓20 minutes for GEO • Quality control and performance assessment • Continuity over the mission lifetime: maintenance of timeliness, quality standards, etc. • Consistency between the different systems • Stability for climate change monitoring
11 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) Requirements for Water Vapour imagery products
The requirement of WV imagery products from each mission are established in the End User RequirementThe Documents (EURD), based on user surveys and approved by council.
Requirements and EURDs are specific for each mission: EURD for MTG: Ref. EUM/MTG/SPE/07/0036 EURD for EPS-SG: Ref. EUM/PEPS/REQ/09/0151
Example of user requirements for METimage products (VIS/IR imagery mission of EPS-SG)
• Global and regional coverage
• Basic Validation scenarios: Clear scenes (Day 1) Parameter Horizontal Vertical Accuracy Continuity Day, night, twilight resolution resolution Water Threshold: 10 km N/A 5% No Sea, land, coast vapour total Breakthrough: 3 km All seasons column Objective: 1 km
• Critical validation scenarios: Cloud contamination Aerosol contamination Dark surface (e.g., ocean) for products retrieved using VIS channels
12 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) Summary of Validation Approach for EUMETSAT water vapour imagery products 3 phases: commissioning, pre-operational, operational/routine 5 groups of reference measurements:
• Radiosonde measurement: ➢ IGRA database (Monalisa, talk by T. August) Current ➢ GRUAN ➢ ARSA In plan
• Ground-based profiling: ➢ GPS (SuomiNet) ➢ Microwave Radiometers (ARN) ➢ Sun-photometers (AERONET, AERONET OC – Coastal, Maritime AERONET – MAN)
• Space-based observations from other LEO/GEO passive instruments: ➢ IASI, MHS, MODIS, AMSU, SSM/IS, IASI-NG, MWS, Sentinel 5 (Low-Earth Orbit) ➢ GOES-16+, MTG/IRS, Sentinel 4 (Geostationary Orbit)
• NWP analysis data ➢ ECMWF analysis / reanalyses
• Dedicated campaigns (if needed, operations only)
13 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) EUMETSAT Needs for future Water Vapour imagery products Focus on user recommendations & support during Pre-launch/Commissioning Phase (2022+)
How do we collaborate with the user community to meet these requirements?Map of IGRA stations EUMETSAT interest in collaboration/discussion with G-VAP
Early dissemination to external partners: • When? Within 2 to 3 weeks after launch • To whom? Among institutes and scientific groups with expertise • Scope: early feedback (before product release) • How? - Official agreement with EUMETSAT - Product quality assessment from a “user” point of view, i.e., evaluation with respect to specific applications (e.g., comments on NetDCF format & content, documentation quality, etc.; trends, statistics, comparison with your own retrievals, etc.) - Provide a report to EUMETSAT before the end of commissioning (~6 months after launch)
Discussion on validation strategy: E.g. Coverage over sea is critical: • Comparison with microwave instruments (e.g., MWS) • Increase the number of stations over sea (shipborne units) • Dedicated campaigns using mobile units
Other points of discussions to trigger the use of EUM WV imagery products in the community (climate applications, etc.): - How is the use of ECMW forecast as prior information in the retrieval perceived by the users? - Is the use of the VIS 0.9µm WV channel beneficial? Product debated for GEO (FCI, GOES-R)
- 14Is the WV imagery retrievalEUMETSAT over Watercloudy Vapor Imageryscenes products beneficial? @ G-VAP Meeting (Madrid, 13/14 June 2019) Summary
➢ EUMETSAT capabilities for water vapour imagery
➢ Summary of current and future water vapour imagery retrievals and products
➢ Validation strategy
➢ Points of discussion and collaborations with the G-VAP community
15 EUMETSAT Water Vapor Imagery products @ G-VAP Meeting (Madrid, 13/14 June 2019) Advertisement
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