swot - LEGOS

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

SWOT

2

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

SWOT

3

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

SWOT

4

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

SWOT

5

Acquisition sites in the Camargue area (2011)

Rhône

Vaccarès

Espiguette (buoy)

Piemanson

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

SWOT

6

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

7

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

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

Phase

SWOT

8

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

10

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

12

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

SWOT

14

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

SWOT

15

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

SWOT

16

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)

SWOT

17

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

SWOT

18