1. No category

Potentials of Bistatic Polarimetric SAR
for Subsurface Imaging in Arid Regions
Philippe PAILLOU
University of Bordeaux, OASU – UMR 5804, France
paillou@obs.u-bordeaux1.fr
POLinSAR 2015, ESA, Frascati, Italy
Arid Regions
“Sub-surface” = bedrock under aeolian deposits
→ geological structures (faults, craters)
→ paleo-climatology (rivers, lakes)
→ natural resources (water, oil)
Subsurface Imaging using SAR
Landsat-TM
SIR-A
(McCauley 1982)
A 900 km-long Paleo-River in Libya
(Paillou 2009)
Two-layers Scattering Problem
Aeolian sediments
Bedrock
I – The Monostatic Case (IEM)
Surface scat.
Volume scat.
Subsurface scat.
(Fung 1992, Fung 1994)
Monostatic Case: Simulation Results
0-10m bedrock
+ 4m sediments
L-band vs.
P-band (HH)
(Paillou 2006)
Monostatic Case: Go to Lower Frequency
II – The Bistatic Case: Geometry
Spherical coordinates:
x = sin(θs) cos(φs)
y = sin(θs) sin(φs)
(Soja 2009)
The Bistatic Case: Surface / Subsurface terms (IEM)
(Fung 2002)
The Bistatic Case: AIEM terms
(Fung 2002, Wu 2008, Soja 2009)
The Bistatic Case: Volume scattering term
(Fung 1994)
A typical 2-layers case for a desert area
f = 1.25 GHz (L-band)
ε1 = 3-0j ε2 = 7-0.1j
σ1 = 0.2 cm L1 = 0.4 cm
σ2 = 1.0 cm L2 = 3.0 cm
W1 = W2 = exponential
a = 0.02 ked = 0.5
Results:
θ = 20o / 40o / 60o
HH / VV / HV pol
σ0surf / σ0vol / σ0subsurf
Surface Scattering Term: HH / VV / HV
θ = 20o
θ = 40o
θ = 60o
Volume Scattering Term: HH / VV / HV
θ = 20o
θ = 40o
θ = 60o
Subsurface Scattering Term: HH / VV / HV
θ = 20o
θ = 40o
θ = 60o
A closer look at θ = 20o: monostatic vs bistatic at VV (1/2)
M
B
M
B
M point = monostatic case VV
θs = -20o, φs = 180o
σ0 surf = -27 dB
σ0 vol = -30 dB
σ0 sub = -13 dB
B point = bistatic case VV
θs = -54o, φs = 60o
σ0 surf = -34 dB
σ0 vol = -97 dB
σ0 sub = -25 dB
→ volume scattering 67 dB lower
M
B
A closer look at θ = 20o: monostatic vs bistatic at VV (2/2)
M
B
M
B
M point = Monostatic case VV
θs = -20o, φs = 180o
σ0 surf = -27 dB
σ0 vol = -30 dB
σ0 sub = -13 dB
B point = Bistatic case VV
θs = 59o, φs = 54o
σ0 surf = -46 dB
σ0 vol = -37 dB
σ0 sub = -29 dB
→ surface scattering 19 dB lower
M
B
Conclusions & Future Work
1) Bistatic SAR presents some
interesting potentials for subsurface
imaging in arid regions, considering
VV polarisation & Brewster effect:
- Volume scattering can be removed
- Surface scattering can be reduced
→ Increase the significance of the
subsurface scattering signal.
2) Need for further modeling and need
for experimental validation, i.e.
measurements over natural sites using
horn antennas and VNA.
3) ESA programmatic context :
SAOCOM-Tango bistatic SAR mission
at L-band provides a unique opportunity.