Compact Polarimetry Potentials
My-Linh Truong-Loï, Jet Propulsion Laboratory /
California Institue of Technology
Eric Pottier, IETR, UMR CNRS 6164
Pascale Dubois-Fernandez, ONERA
IGARSS’11
Overview
• Definition of compact polarimetry mode
• Calibration of a compact-pol system
• Simulation of compact-pol data from full-pol raw data
• Estimation of biomass with compact-pol data
IGARSS’11
Issues
•
Compact polarimetry
– 1 polarization on transmit
– 2 polarizations on receive
•
What is the best polarization on transmit?
•
What are the best polarizations on receive?
•
How do we analyze the data?
– Calibration
– Faraday Rotation
– Geophysical parameter estimation
IGARSS’11
Background - Example with ALOS system
•
•
•
Mode
Swath
Resolution
Incidence
angle
HH
70km
10m
8° ~ 60°
HH/HV or
VV/VH
(dual-pol)
70km
20m
8° ~ 60°
Full polar
(quad-pol)
30km
30m
8° ~ 30°
Single polarisation  large swath and larger incidence angle range
Full polarisation  added characterisation
Compact polarisation  full investigation of the dual-pol alternative
IGARSS’11
Background - Compact Polarimetry 1/2
• π/4 mode: one transmission at 45° and two coherent polarizations in
reception (linear H & V, circular right & left,…)
• π/2 mode: one circular transmission and two coherent polarizations in
reception (linear H & V, circular right & left,…)
 k  1  S HH
k  1

2  SVH
 k2 
S HV   1  1  S HH  jS HV 




SVV    j 
2  SVH  jS VV 
• Hybrid polarity : particular case of π/2 : one circular transmission and two
coherent linear polarizations in reception (H&V)
IGARSS’11
Background - Compact Polarimetry 2/2
•
/4-mode potentials: reconstruction of the PolSAR information (1)
– Iterative algorithm based on:
• Reflection symmetry
• Coherence between co-polarized channels
•
/2-mode potentials: avoid Faraday rotation in transmission (2)
– Transmit a circular polarized wave
– Show results about the reconstruction of the PolSAR information from /2 mode
– Applications possible (3) :
• Faraday rotation estimate
• Soil moisture estimate
• Classification using the conformity coefficient
•
Hybrid polarity potentials: decomposition of natural targets (4)
–
(1)
(2)
(3)
(4)
m-d method based on Stokes parameters
J-C. Souyris, P. Imbo, R. FjØrtoft, S. Mingot and J-S. Lee, Compact Polarimetry Based on Symmetry Properties of Geophysical
Media: The /4 Mode, IEEE Transactions on Geoscience and Remote Sensing, vol. 43, no. 3, March 2005.
P. C. Dubois-Fernandez, J-C. Souyris, S. Angelliaume and F. Garestier, The Compact Polarimetry Alternative for Spaceborne
SAR at Low Frequency, IEEE Transactions on Geoscience and Remote Sensing, vol. 46, no. 10, October 2008.
M-L Truong-Loï, A.Freeman, P. C. Dubois-Fernandez and E. Pottier, Estimation of Soil Moisture and Faraday Rotation from
Bare Surfaces Using Compact Polarimetry, IEEE Transactions on Geoscience and Remote Sensing, vol. 47, no. 11, Nov. 2009.
R. K. Raney, Hybrid-Polarity SAR
Architecture, IEEE Transactions on Geoscience and Remote Sensing, vol. 45, no. 11,
IGARSS’11
November 2007.
Overview
• Definition of compact polarimetry mode
• Calibration of a compact-pol system
• Simulation of compact-pol data from full-pol raw data
• Estimation of biomass with compact-pol data
IGARSS’11
Calibration – Full-pol system
•
Full-pol system calibration : 7 unknowns δ1, δ2, δ3, δ4, Ω, f1, f2
M  A r,  e j DR RSR DT  N
 1 d 2  cos sin   S HH


M  Ar , e j 
d
f

sin

cos

 S HV
 1 1 
•
SVH  cos sin   1 d 3 

 N

SVV   sin  cos  d 4 f 2 
The S matrix can be recovered:
S  R1DR1MDT1R1
•
Distorsions can be retrieved with measures over known targets:
– Trihedral, dihedral, transponder, natural targets, etc.
A. Freeman et T. Ainsworth, Calibration of longer wavelength polarimetric SARs, Proceedings of EUSAR 2008, Friedrishafen, Allemagne, June
2008.
S. Quegan, A Unified Algorithm for Phase and Cross-Talk Calibration of Polarimetric Data – Theory and Observations, IEEE Transactions on
Geoscience and Remote Sensing, vol. 32, no. 1, pp. 89-99, January 1994.
J. J. van Zyl, Calibration of Polarimetric Radar Images Using Only Image Parameters and Trihedral Corner Reflector Responses, IEEE
Transactions on Geoscience and Remote Sensing, vol. 28, no. 3, pp. 337-348, May 1990.
IGARSS’11
Calibration – Compact-pol system
• Compact polarimetric system:
M
1
1
A  r ,  e j DR R SR DT    N
2
 j
R1DR1M 
 1 
1
SR DT  
2
 j
• The transmission defects cannot be corrected a posteriori
• System needs to be of high quality before transmission
• With a high-quality transmission  4 unknowns d1, d2, , f1
M
1
1
A  r ,  e j DR R SR    N
2
 j
IGARSS’11
Calibration – Compact-pol system
M  Ae j e  j
•
 S  j  d1  
1  S HH cos  d1 sin   jSVV sin   d1 cos 

  Ae j  HV



S

j
d

f
2  S HH d 2 cos  f1 sin   jSVV d 2 sin   f1 cos
2
1 
 HV
Compact polarisation
– 3 reference targets are necessary
• Dihedral @ 0°
• Dihedral @ 45°
• Trihedral
•
D
D
M RV
j  M D M D M RH
d1   RV0 RV

D
D
D0
2  M D M RH
M
M
RV
RH
 RH
0
0
f1 




2j
T
M RH
T
M RV

D
M RH
D
M RV
Full polarisation
–
–
–
–
More unknowns
But less targets are required
Natural targets can be used
Acquisition of both HV and VH
IGARSS’11
1
 D0 T 
D0
D
 
M RV
M RV
j  M RH
A
j
   ln
2 j 
0
0
D
 
2  M D AD  M D M RH
RH

 
 RV
0
d 2  f1
2
D
M RH
0
D
M RV
 d1* f1  jf1
Overview
• Definition of compact polarimetry mode
• Calibration of a compact-pol system
• Simulation of compact-pol data from full-pol raw data
• Estimation of biomass with compact-pol data
IGARSS’11
Simulated compact polarimetric data
• Simulation of CP data is necessary
• How do we proceed?
– Two options:
• From raw data
• From processed data
• Comparison between the two
approaches
Example of raw data, range spectra HH
{R;G;B}={HH;HV;VV}, SETHI data, L-band, Garons
IGARSS’11
Building compact polarimetric data
Process 1
S HH raw
Processing
(corrections,
antenna beam, etc.)
Process 2
S HV raw
M RH  SHH  jSHV
SHH raw
S HV raw
Hilbert
transform
Processing
(corrections,
antenna beam, etc.)
 jSHVraw
S HV p ro
SHH p ro
k RH raw  S HH raw  j
A _ HV
S HV raw
A _ HH
Processing
(corrections,
antenna beam, etc.)
Calibration:
 SHH A _ HV

k RH pro  A _ HH  S HH pro  j
S HV pro 
A _ HH


raw
Calibration:
Raw data
Processed data
MRHpro
IGARSS’11
kRH  A _ HH  kRHraw
MRH
Building CP data - Process 1 / Process 2
Image of CP data from FP processed data, {R ;G ;B}={ MRh_pro+MRv_pro ;MRh_pro ;MRv_pro }
RHMM RH
raw pro
Image of CP data from FP raw data, {R ;G;B}={ MRh+MRv ;MRh ;MRv }
0
Coherence between both images
IGARSS’11
1
Compact-pol - Process 2 / Process 2
FP data {R;G;B}={<|VV|²>;<|HV|²>;<|HH|²>}
FP reconstructed {R;G;B}={<|VV|²>;<|HV|²>;<|HH|²>}
IGARSS’11
Overview
• Definition of compact polarimetry mode
• Calibration of a compact-pol system
• Simulation of compact-pol data from full-pol raw data
• Estimation of biomass with compact-pol data
IGARSS’11
Backscattering coefficients and biomass – RAMSES Pband data over Nezer forest
(HV)
(HV)
(RH)
(RR)
IGARSS’11
Biomass estimate – Nezer forest
Polarization
RMS error (tons/ha)
quadratic regression
RMS error (tons/ha)
exponential regression
HV
5.8
5.7
HV
6.2
6.5
RR
6.6
6.6
RH
12.2
12.8
RMS error = 2.6 tons/ha (HV vs HV)
IGARSS’11
Biomass map – Nezer forest
120 tons/ha
0
BHV  205.8e0.1274 HV
BHV  178.01e
IGARSS’11
0.1465 HV
BRR  53.142e0.1626 RR
Biomass map – Nezer forest
120 tons/ha
0
Measured biomass
BHV
IGARSS’11
BHV
BRR
Biomass estimate with HV regression
Using the HV regression as a reference, computation of the biomass with HV
backscattering coefficient
RMS error=20.1 tons/ha
Bias=19.5 tons/ha
IGARSS’11
Summary: systems implications
• Compact-pol allows
– To acquire larger swath (versus FP)
– To access wider incidence angle range (versus FP)
– To avoid Faraday rotation in transmission (versus DP)
• Calibration
– A solution with 3 external targets
• Raw data
– Equivalence between CP from FP raw data and from FP processed data
• Biomass estimate
– FP: RMS error for HV: 5.8 tons/ha
– CP: RMS error for HV reconstructed: 6.3 tons/ha
– CP: RMS error for RR: 6.6 tons/ha
IGARSS’11
Thank you
for your attention
IGARSS’11