Validation_SWOT_ground_airborne_Fjortoft.ppt

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


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


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, …


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


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


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


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)



Phase



Coherence

>0.9~0.7

~0.3


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


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

Amplitude 1 Amplitude 2 Coherence Phase


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

Amplitude


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

Amplitude 1 Amplitude 2 Coherence Phase




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.


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)


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)


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


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

Validation_SWOT_ground_airborne_Fjortoft.ppt

Technology

field kaband acquisitions

band backscattering

rhne amplitude

near nadir

band fewer surfaces

simulation backscattering

nadir acquisitions

specificities of near