From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science...
Transcript of From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science...
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From METOP ASCAT to METOP-SG SCA: Science Needs over Land
Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil
Department of Geodesy and Geoinformation (GEO)Vienna University of Technology (TU Wien)
http://www.geo.tuwien.ac.at/
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European C-Band Scatterometer Series
AMI Scatterometer
Frequency: 5.3 GHzPolarisation: VV
Resolution: 50 kmDaily coverage: <40%
SatellitesERS-1: 1991-2000ERS-2: 1995-2011
METOP ASCAT
Frequency: 5.255 GHzPolarisation: VV
Resolution: 25 kmDaily coverage: 82%
SatellitesMETOP-A: 2006 ongoingMETOP-B: 2012 ongoingMETOP-C: 2018
METOP-SG SCA
Frequency: 5.355 GHzPolarisation: VV + VH + HH
Resolution: ~12.5 kmDaily coverage: ~88%
SatellitesMETOP-SG-B1: 2022 METOP-SG-B2: 2030
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SCA Research & Development Needs
General• Use of VH and HH to improve backscatter models over land• Exploitation of improved spatial resolution and temporal sampling
Improved vegetation modelling by using VH/VV and other polarisation indices to complement information content of slope
• In radiative transfer vegetation is modelled using at least to parameters: optical depth and scattering albedo
• Goal: Self-standing vegetation products & improved soil moisture retrievals Characterisation of sub-surface scattering
• Robust identification of occurrence of phenomenon• Goal: Soil mapping & improved soil moisture retrievals
Other R&D Needs• Freeze/thaw monitoring in NRT• Detection of inundation and dynamic water bodies• Use of backscatter echoes stemming only from soil moisture sensitive areas
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How to Advance Beyond the State of Art?
Knowledge about C-band backscatter still dominated by insights gained from experimental studies using only few, intermittent SAR images
• Focus on (spatial) details may distort one’s understanding of the “big picture”
How to overcome this?• Analysis of dense & long time series of existing satellite data over sufficiently
large/diverse regions– ASCAT: from 2018 three satellites in orbit– Sentinel-1: VV+VH combination
• Experimental ranging radar systems– Airborne– Ground-based
• Theoretical modelling
Incomplete and partly wrong understanding of vegetation and soil scattering phenomena
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Hydrological Open Air Laboratory (HOAL)
A hydrological observatory for interdisciplinary research in Petzenkirchen, Austria. Aerial picture of the HOAL viewing North, courtesy of Alexander Eder.
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ASCAT Soil Moisture over HOAL
Current operational H-SAF product: Seasonal biases (summers too wet)
Improved vegetation correction: Elimination of seasonal biases
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Sentinel-1 VH Sensitivity to Vegetation Cover
RGB composite of VH backscatter at April, May and June, including land cover and Sampling Units.
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Sentinel-1 CR = VH/VV for Different Crop Types
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Backscatter Dynamics over Agriculture and Forests
Dostálová et al. (2017) Annual seasonality in Sentinel-1 signal for forest mapping and forest type classification, submitted.
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Airborne Nadir-Looking Ku-Band Profiling Radar
Tomoradar built and operated by FGIPiermattei et al. (2017) An analysis of Ku-band profiling radar observations of boreal forest, in prep.
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ASCAT over An Nafud Desert
Presented @ IGARSS’12
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Tomographic Profiling
At the GB-SAR Microwave Measurement Facility C-band VV tomographic profiling (TP) measurements were collected of trihedral and a pile of cobble stones
Morrison (2013) Mapping Subsurface Archaeology with SAR, Archaeological Prospection, 20, 149–160.
Example C-band TP image of a soil troughTP image showing the presence of various features in the soil volume. The soil surface is at 150cm.
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Soil Surface Scattering
Existing scattering models, e.g. IEM, assume a hard boundary between the air (with ε0) and soil (with εsoil)
Recent research has demonstrated the importance of considering an air-soil transition zone
• Allows simulating a linear relationship between backscatter (in dB) and soil moisture content
• Effective “soil surface roughness” dependent on soil moisture
Schneeberger et al. (2004) Topsoil structure influencing soil water retrieval by microwave radiometry, Vadose Zone Journal, 3(4), 1169-1179.
Air-to-Soil Transition Model
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RT1 Scattering Model
Radiative transfer model for bi- and monostatic scattering Generalised phase functions for modelling surface-volume interactions Available on GitHub: https://github.com/TUW-GEO/rt1
Quast, R., W. Wagner (2016) An analytical solution for first-order scattering in bistatic radiative transfer interaction problems of layered media, Applied Optics, 55(20), 5379-5386.
𝐼𝐼𝑖𝑖𝑖𝑖𝑖𝑖 ∝ �⋯ 𝒫𝒫𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 � 𝒫𝒫𝑣𝑣𝑣𝑣𝑣𝑣 𝑑𝑑𝑑𝑑 𝑑𝑑𝑑𝑑
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Vegetation Scattering
Soil Scattering
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Outlook
ASCAT and Sentinel-1 allow studying C-band co-pol and cross-pol backscatter in preparation for SCA
Scientific prospects• Unravelling the effects of vegetation structure and water content, soil surface
roughness and sub-surface scattering on backscatter Potential synergistic products
• Soil moisture, vegetation (optical depth, water content, phenology), freeze/thaw, etc.
ESCAT+ASCAT+SCA → High stability climate data records 1991-2045
AcknowledgementsEUMETSAT: H-SAF CDOP3H2020: Advanced SAR (Grant #606971)ESA: CCI Soil Moisture Phase 2Austrian Space Application Programme: “VegetationDynamics”Austrian Science Fund: Vienna Doctoral Programme on Water Resources Systems