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
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
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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
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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
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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
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Acquisition sites in the Camargue area (2011)
Rhône
Vaccarès
Espiguette
(buoy)
Piemanson
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
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DRIVE/BUSARD acquisition 24/02/2011 (Rhône)
voie a 0°
0°
~1°
~4°
Artifacts due to wide
antenna lobe (right/
left contamination)
~700 m
~10°
Trihedrals
~2,6 km
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
Amplitude
13°
SWOT
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DRIVE/BUSARD acquisition 24/02/2011 (Rhône)
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
Phase
SWOT
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DRIVE/BUSARD acquisition 24/02/2011 (Rhône)
~0.3
>0.9
~0.7
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
Coherence
SWOT
9
DRIVE/BUSARD acquisition 14/04/2011 (Vaccarès)
Amplitude
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
SWOT
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DRIVE/BUSARD acquisition 14/04/2011 (Vaccarès)
Amplitude 1
Amplitude 2
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
Coherence
Phase
SWOT
11
DRIVE/BUSARD acquisition 14/04/2011 (Espiguette)
Amplitude
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
SWOT
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DRIVE/BUSARD acquisition 14/04/2011 (Espiguette)
Amplitude 1
Amplitude 2
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
Coherence
Phase
SWOT
13
DRIVE/BUSARD acquisition 25/05/2011 (Rhône)
Amplitude
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
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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
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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
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Water 0 as a function of wind speed
Wind parallel to incidence direction
0 (dB)
0 (dB)
Wind perpendicular to incidence direction
Incidence (°/100)
IGARSS 2011, Vancouver, Canada, 25-29 July 2011
Incidence (°/100)
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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 surfaces
 0 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
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