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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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From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

Sep 07, 2020

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Page 1: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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/

Page 2: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil
Page 3: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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

Page 4: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil
Page 5: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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

Page 6: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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

Page 7: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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.

Page 8: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

ASCAT Soil Moisture over HOAL

Current operational H-SAF product: Seasonal biases (summers too wet)

Improved vegetation correction: Elimination of seasonal biases

Page 9: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

Sentinel-1 VH Sensitivity to Vegetation Cover

RGB composite of VH backscatter at April, May and June, including land cover and Sampling Units.

Page 10: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

Sentinel-1 CR = VH/VV for Different Crop Types

Page 11: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

Backscatter Dynamics over Agriculture and Forests

Dostálová et al. (2017) Annual seasonality in Sentinel-1 signal for forest mapping and forest type classification, submitted.

Page 12: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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.

Page 13: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

ASCAT over An Nafud Desert

Presented @ IGARSS’12

Page 14: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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.

Page 15: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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

Page 16: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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

Page 17: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

Vegetation Scattering

Soil Scattering

Page 18: From METOP ASCAT to METOP-SG SCA: Science Needs ......From METOP ASCAT to METOP-SG SCA: Science Needs over Land Wolfgang Wagner, Sebastian Hahn, Stefano Elefante, Mariette Vreugdenhil

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