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

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 5SWOT

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 6SWOT

Espiguette (buoy)

Acquisition sites in the Camargue area (2011)

Piemanson

Vaccarès

Rhône

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 7SWOTAmplitude

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 8SWOT

DRIVE/BUSARD acquisition 24/02/2011 (Rhône)

Phase (interferogram)

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 9SWOT

DRIVE/BUSARD acquisition 24/02/2011 (Rhône)

Coherence

>0.9~0.7

~0.3

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 10SWOTAmplitude

DRIVE/BUSARD acquisition 14/04/2011 (Vaccarès)

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 11SWOT

DRIVE/BUSARD acquisition 14/04/2011 (Vaccarès)

Amplitude 1 Amplitude 2 Coherence Phase

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 12SWOT

DRIVE/BUSARD acquisition 14/04/2011 (Espiguette)

Amplitude

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 13SWOT

DRIVE/BUSARD acquisition 14/04/2011 (Espiguette)

Amplitude 1 Amplitude 2 Coherence Phase

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 14SWOTAmplitude

DRIVE/BUSARD acquisition 25/05/2011 (Rhône)

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 15SWOT

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 16SWOT

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 17SWOT

Water 0 as a function of wind speed

Incidence (°/100)

0 (

dB

)

Wind parallel to incidence directionWind perpendicular to incidence direction

0 (

dB

)

Incidence (°/100)

IGARSS 2011, Vancouver, Canada, 25-29 July 2011 18SWOT

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