Validation_SWOT_ground_airborne_Fjortoft.ppt
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Validation of radiometric models and simulated KaRIn/SWOT
data based on ground and airborne acquisitions
Roger Fjørtoft, Jean-Claude Lalaurie, Nadine Pourthie, Christine Lion, Jean-Marc Gaudin, Alain Mallet (CNES, Toulouse, France),
Jean-François Nouvel, Pierre Borderies (ONERA, Toulouse/Salon de Provence, France), Pascal Kosuth (CEMAGREF, Montpellier, France),
Christian Ruiz (Capgemini, Toulouse, France).
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 2SWOT
Outline■ Introduction
Context, objectives Specificities of KaRIn/SWOT
interferometric SAR data
■ Modeling and simulation Backscattering from various surfaces Simulation of raw and SLC radar images
■ Airborne acquisitions First interferometric Ka-band acquisitions
including the KaRIn incidence range (1-4°)
■ Near-field Ka-band measurements Water backscattering as a function of
wind speed and surface roughness
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 3SWOT
Introduction
■ Context Original InSAR configuration of KaRIn/SWOT: Ka-band, near-nadir (1-4°)
Very limited bibliography on backscattering from natural surfaces Modeling of Ka-band backscattering (0)
As a function of surface type, surface conditions, incidence angle, … Simulation of raw (L0) and SLC (L1) KaRIn/SWOT interferometric data
Radiometry and geometry
■ Objective: Realize airborne and near-field Ka-band acquisitions Compare models and simulations with real data (validate, improve)
Need for ground truth Study important phenomena w.r.t. feasibility and performance
Coherence, land/water contrast, layover, … Enable more realistic input data for algorithm development and testing
Airborne data and improved simulated images
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 4SWOT
Specificities of KaRIn interferometric SARw.r.t. existing spaceborne earth observation SAR systems
■ Ka-band (wavelength of only 8.6 mm) [compared to X-, C-, L-band] Fewer surfaces appear smooth, implying less specular reflection Weaker penetration into vegetation, soil, snow,… Higher sensitivity to tropospheric conditions; rain will generally make
acquisitions useless A smaller baseline can be used for interferometry (10 m mast) Few reports on backscattering from natural surfaces, especially in
■ Near nadir (0.6-4.1° incidence) [typically 20-50° for spaceborne SAR] Layover even in zones of moderate topography (terrain slope > incidence) Inversion of land/water radiometric contrast (water > land) Strong relative incidence variation, implying strong/rapid range variation in
several key parameters (pixel size, altitude of ambiguity, orbital fringes, …)
■ For more details, refer to: R. Fjørtoft et al., “Specificities of Near-nadir Ka-band Interferometric SAR Imagery”, Proc. EUSAR 2010.
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 5SWOTSAR images Coherence Interferogram
Simulation of SLC images (L1)■Radiometric simulator: Simulation of RCS for different surface
types in various conditions (sensitivity studies, case studies) water surfaces, bare soil, trees, grass, aquatic vegetation, ice, snow (and combinations)
■Geometric simulator Integrates results of radiometric simulator Geometric effects such as layover and shadow Simulation of interferometric pairs of SLC images
DEMLand cover classes
EM models
Orbit file
ar
Layover/ shadow mask
e.g. detection of water surfaces, height estimation, …
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 6SWOT
ΔT = t0 – t-1 = t+1 – to = 1 / PRF
→V
t-1to
t+1
RCSt-1
RCSto
RCSt+1
Stacking of all raw images
indexed by time
Focusing
Final RAW data
level 1 data
Simulation of raw images (L0)
e.g. study impact of moving water
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 7SWOT
BUSARD/DRIVE airborne acquisitions (1/2)
■BUSARD is a Stemme motor-glider operated by ONERA■DRIVE Ka-band radar integrated in POD■ Interferometry with short (18 cm) or
long (4.7 m) baseline■2.5 W amplifier
■Near-nadir acquisitions (0-14°) with 18 cm baseline in 2011
■Altitude: 3000 m (9500 ft)■Swath: 700 m ■Acquisition length: 5 km (2 min)■PRF: 1250 Hz■ Integration time: 0.2 s
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 8SWOT
BUSARD/DRIVE airborne acquisitions (2/2)
■Simultaneous ground truth: Wind speed Water surface roughness Water surface height and slope Wave height (buoys) Soil humidity
■Same day/week/month: Soil roughness Vegetation characteristics Landcover
■Available static data: Digital maps DEM
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 9SWOT
Espiguette (buoy)
Acquisition sites in the Camargue area (2011)
Piemanson
Vaccarès
Rhône
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 10SWOTAmplitude
voie a
~700 m
0°
13°~2,6 km
~1°
0°
~4°
~10°
Trihedrals
Artifacts due to wide antenna lobe (right/left contamination)
DRIVE/BUSARD acquisition 24/02/2011 (Rhône)
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 11SWOT
DRIVE/BUSARD acquisition 24/02/2011 (Rhône)
Phase
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 12SWOT
DRIVE/BUSARD acquisition 24/02/2011 (Rhône)
Coherence
>0.9~0.7
~0.3
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 13SWOTAmplitude
DRIVE/BUSARD acquisition 14/04/2011 (Vaccarès)
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 14SWOT
DRIVE/BUSARD acquisition 14/04/2011 (Vaccarès)
Amplitude 1 Amplitude 2 Coherence Phase
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 15SWOT
DRIVE/BUSARD acquisition 14/04/2011 (Espiguette)
Amplitude
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 16SWOT
DRIVE/BUSARD acquisition 14/04/2011 (Espiguette)
Amplitude 1 Amplitude 2 Coherence Phase
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 17SWOTAmplitude
DRIVE/BUSARD acquisition 25/05/2011 (Rhône)
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 18SWOT
Near-field measurements in Ka-band (1/2)
■Near-field Ka-band measurements of 0 of water with a network analyzer and an automatically steerable (0-10°) parabolic antenna (ONERA)
■Simultaneous measurement of water surface roughness (using immerged pressure sensors) and wind speed (CEMAGREF)
■Rapidly varying wind conditions make the interpretation of the first results complicated.
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 19SWOT
Near-field measurements in Ka-band (2/2)
■Acquisitions in the Large Air-Sea Interaction Facility (LASIF) at IRPHE (Luminy): 40 m wind tunnel + 40 m water tank
■Possibility to study wind-generated water roughness (waves) in stable conditions (as well as to add mechanically generated waves)
■Additional equipment for optical roughness characterization (IRPHE)
■Comparison of 0 profiles with radiometric models (CapGemini)
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 20SWOT
Water 0 as a function of wind speed
Incidence (°/100)
0 (d
B)
Wind parallel to incidence directionWind perpendicular to incidence direction
0 (d
B)
Incidence (°/100)
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 21SWOT
Conclusion
■Airborne acquisitions with DRIVE/BUSARD First interferometric Ka-band acquisitions including the near-nadir
incidence range of KaRIn/SWOT (1-4°) Confirmation of main feasibility and measurement physics assumptions Will allow to refine models and simulators Experience gained w.r.t. InSAR processing and ground truth collection Hydrology, coastal and ocean test sites covered; possible extension to other
surface types: forest, snow/ice, …
■Near field measurements of water surfaces0 as a function of incidence and wind speed / surface roughness
Interesting phenomena observed; comparison with models ongoing Wind-generated roughness only; possibility of adding waves mechanically Complementary in situ and wind/water tank measurements
IGARSS 2011, Vancouver, Canada, 25-29 July 2011 22SWOT
SWOT-related presentations in other sessions
■EXTRACTION OF WATER SURFACES IN SIMULATED KA-BAND SAR IMAGES OF KARIN ON SWOT
Authors: Fang Cao, Florence Tupin, Jean-Marie Nicolas, Roger Fjørtoft, Nadine Pourthié
Session: SAR Image Processing I Thursday, July 28, 09:20, Ballroom A
■MODELING AND APPLICATIONS OF SWOT DATA Authors: Christine Lion, Konstantinos Andreadis, Roger Fjørtoft,
Florent Lyard, Nadine Pourthié, Jean-François Crétaux Session: Wetlands and Inland Waters II Thursday, July 28, 13:40, Room 12