POTENTIALS OF A COMPACT POLARIMETRIC SAR SYSTEM
My-Linh Truong-Loï, ONERA/CNES/IETRPascale Dubois-Fernandez, ONERAEric Pottier, IETR – UMR CNRS 6164
Anthony Freeman, JPLJean-Claude Souyris, CNES
IGARSS 20102
Objectives
Missions dedicated to global environmental
change monitoring
Low frequency
radar
Ionosphere interaction Faraday
rotation Compact polarimetry
Transmitting a circular
polarized wave
No depolarization anymore
Receiving two orthogonal
polarized waves
Estimate Faraday rotation
High power of
penetration
Dual-pol system
Large swath
Dual-pol system
IGARSS 20103
Outline
• Background – compact polarimetry
• Faraday rotation estimate• Bare soil surfaces selection• Faraday rotation estimate
• PolSAR applications• Soil moisture estimate• Biomass estimate
• PolInSAR applications• Forest height estimate
• Calibration
IGARSS 20104
Background - Compact Polarimetry 1/2
• π/4 mode: one transmission at 45° and two orthogonal receptions (linear H & V, circular right & left,…)
• π/2 mode: one circular transmission and two orthogonal receptions (linear H & V, circular right & left,…)
• Hybrid polarity : particular case of π/2 : one circular transmission and two linear receptions (H&V)
1
2
11 1
2 2HH VH HH VH
HV VV HV VV
S S S jSkk
S S S jSk j
IGARSS 2010
• π/4-mode potentials: reconstruction of the PolSAR information (1)• Iterative algorithm based on:
• Reflection symmetry• Coherence between co-polarized channels
• π/2-mode potentials: avoid Faraday rotation in transmission (2)• Transmit a circular polarized wave• Adaptation of the reconstruction of the PolSAR information is possible
• Hybrid polarity potentials: decomposition of natural targets (3)• m-δ method based on Stokes parameters
Background - Compact Polarimetry 2/2
(1) J-C. Souyris, P. Imbo, R. FjØrtoft, S. Mingot and J-S. Lee, Compact Polarimetry Based on Symmetry Properties of Geophysical Media : The π/4 Mode, IEEE Transactions on Geoscience and Remote Sensing, vol. 43, no. 3, Mars 2005.
(2) P. C. Dubois-Fernandez, J-C. Souyris, S. Angelliaume et F. Garestier, The Compact Polarimetry Alternative for Spaceborne SAR at Low Frequency, IEEE Transactions on Geoscience and Remote Sensing, vol. 46, no. 10, Octobre 2008.
(3) R. K. Raney, Hybrid-Polarity SAR Architecture, IEEE Transactions on Geoscience and Remote Sensing, vol. 45, no. 11, Novembre 2007.
IGARSS 20106
Conclusion
• π/2 mode is required for low frequency spaceborne radar
How to estimate/correct for Faraday rotation in reception ?
Bare soil surfaces are first required
IGARSS 20107
The conformity coefficient
Double-bounce Volume Surface
SHV ~ 0
SHH, SVV correlated
Arg<SHHSVV*> ≈ 180°
-1< μ< t2
SHV is significant
SHH, SVV less correlated
t2< μ<t1
SHV ~ 0
SHH, SVV correlated
Arg<SHHSVV*> ≈ 0
t1<μ<1
222
2*
**
*
2
)Re(2
Im2
VVHVHH
HVVVHH
RVRVRHRH
RVRH
SSS
SSS
MMMM
MM
• This coefficient• Can be shown to be FR independent• can be used with CP data as well as FP data• discriminates 3 different types of scattering
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, Novembre 2009.
IGARSS 20109
Conformity coefficient vs Cloude-Pottier and Freeman-Durden classifications, RAMSES P-band data over St Germain d’Esteuil, France
Conformity coefficientCloude-Pottier classification Freeman-Durden classification
VolumeDouble-bounce Surface
S. R. Cloude et E. Pottier, A Review of Target Decomposition Theorems in Radar Polarimetry, IEEE Transactions on Geoscience and Remote Sensing, vol. 34, no. 2, Mars 1996.
A. Freeman et S. L. Durden, A Three-Component Scattering Model for Polarimetric SAR Data, IEEE Transactions on Geoscience and Remote Sensing, vol. 36, no. 3, Mai 1998.
•Pv > 0.6 Pd & Pv > 0.3 Ps
•Ps>Pd
•Pd
IGARSS 201010
Conclusion
• π/2 mode is required for low frequency spaceborne radar• Introduction of a parameter : the conformity coefficient
• Is FR-independent• Allows to distinguish 3 types of scattering
We can select bare soil surfaces with compact-pol data
Is it now possible to correct for FR with compact-pol data ?
IGARSS 201011
Flow diagram of the process
e
FP calibrated data (Ramses, PALSAR)
Select bare surfaces(by using the conformity coefficient)
Estimate the Faraday rotation
Synthesized CP data (add Faraday rotation)
(1) (2)
(3)
*1arg mod
2 2RR RLM M
*
* *
1arctan 2 mod
2 4RH RV
RV RV RH RH
e M M
M M M M
*arg mod2RH RVS S
IGARSS 201012
Faraday rotation estimate over PALSAR L-band data
Full polarimetric dataOver bare surfaces μ>0.2
Compact polarimetric data
Thanks to the ASF for providing the data.
4
4
4
IGARSS 201013
Conclusion
• π/2 mode is required for low frequency spaceborne radar• Introduction of a parameter : the conformity coefficient
• Is FR-independent• Allows to distinguish 3 types of scattering
• Estimation of FR over bare surfaces identified by the conformity coefficient
Now FR is corrected
Can we use this type of data ?• Let’s see PolSAR applications
• 1) soil moisture estimate
IGARSS 201014
FP vs CP signatures
VV
HH
RV
RH
jS
S
S
S~
~
SHV ~ 0 over bare soil surfacesσ H
h (d
B)
σRh (dB)
10
10-30
-30 10
10
σ Vv (d
B)
σRv (dB)
Window size : 7x7 σHh/ σRh
σVv/ σRv
Stdv: <2dB
RH HH HV
HV VVRV
S S jS
S jSS
IGARSS 201015
FP vs CP soil moisture – Dubois et al. algorithm
FP soil moisture0 100%
100%
CP
soi
l moi
stur
e
Stdv : 4%
CP/FP soil moisture Estimated soil moisture CP & FP vs ground truth
Stdv : 2%
RAMSES L-band data, Le Moulin du Fâ, France
AIRSAR/WASHITA L-band data over Chickasha area
P. C. Dubois, J. van Zyl et T. Engman, Measuring Soil Moisture with Imaging Radars, IEEE Transactions on Geoscience and Remote Sensing, vol. 33, no. 4, pp. 915-926, Juillet 1995.
IGARSS 201016
Conclusion
• π/2 mode is required for low frequency spaceborne radar• Introduction of a parameter : the conformity coefficient
• Is FR-independent• Allows to distinguish 3 types of scattering
• Estimation of FR over bare surfaces identified by the conformity coefficient
• Compact PolSAR applications:• Estimate of soil moisture is possible over bare surfaces selected by μ
and using Dubois et al. Algorithm – RMS error of 2% over AIRSAR L-band data
Can we use this type of data ?• Let’s see PolSAR applications
• 1) soil moisture estimate• 2) biomass estimate (FP, FP reconstructed from CP and CP)
IGARSS 201017
Backscattering coefficients vs measured biomass – RAMSES P-band data over Nezer forest
(HV)
(RR) (RH)
IGARSS 201018
Biomass estimate vs in situ measurements – Nezer forest
RMS error=6.25 tons/ha
RMS error=6.63 tons/ha RMS error=12.2 tons/ha
RMS error=5.8 tons/ha
IGARSS 201019
Biomass map – Nezer forest
HVeBHV1274,08,205
'1465,0' 01,178 HVeBHV
RReBRR1626,0142,53Measured biomass
0 120 tons/ha
IGARSS 201020
ROI biomass map – Nezer forest
Measured biomass BHV BHV’BRR
IGARSS 201021
Conclusion
• π/2 mode is required for low frequency spaceborne radar• Introduction of a parameter : the conformity coefficient
• Is FR-independent• Allows to distinguish 3 types of scattering
• Estimation of FR over bare surfaces identified by the conformity coefficient
• Compact PolSAR applications:• Estimate of soil moisture is possible over bare surfaces selected by μ and
using Dubois et al. Algorithm – RMS error of 2% over AIRSAR L-band data• Quantify biomass with HV’ (RMS error : 6,25 tons/ha) and RR (6,63 tons/ha)
instead of HV (5,8 tons/ha)
• Add interferometry concept compact-PolInSAR potentials
IGARSS 201022
Compact-PolInSAR vs full-PolInSAR
• Compact-PolInSAR (C-PolInSAR) information is represented by a 4x4 matrix
• Full-PolInSAR (F-PolInSAR) information is represented by a 6x6 matrix
IGARSS 201023
PolInSAR applications – vegetation height estimate
• Flynn et al. algorithm
max j
we
Tww
wewe
T
jTj
*12
*
22211 TT
T
* *12 12
** *11 22
( )T T
TT T
w w w ww w
w Tww T w w T w
11 126 *
12 22T
TC
T
T. Flynn, M. Tabb et R. Carande, Estimation of Coherence Region Shapes in Polarimetric SAR Interferometry, AIRSAR Workshop, Mars 2002.
IGARSS 201024
Phase centers height (FP & CP)
Phase centers height FP
Phase centers height CP
Nezer forest, P-band
IGARSS 201025
Vegetation height – Nezer forest P-band
S.R. Cloude and K.P. Papathanassiou, A 3-Stage Inversion Process for Polarimetric SAR Interferometry, IEE Proceedings Radar, Sonar & Navigation, vol. 150, no. 3, June 2003.
RMS : 1m, Bias : 0,4m (FP)
RMS : 1,1m, Bias : 0,4m (CP)
RMS : 2,45m, Bias : -1,8m (FP)
RMS : 2,5m, Bias : -1,78m (CP)
IGARSS 201026
Conclusion
• π/2 mode is required for low frequency spaceborne radar• Introduction of a parameter : the conformity coefficient
• Is FR-independent• Allows to distinguish 3 types of scattering
• Estimation of FR over bare surfaces identified by the conformity coefficient
• Compact PolSAR applications:• Estimate of soil moisture is possible over bare surfaces selected by μ and
using Dubois et al. Algorithm – RMS error of 2% over AIRSAR L-band data• Quantify biomass with HV’ (RMS error : 6,25 tons/ha) and RR (6,63 tons/ha)
instead of HV (5,8 tons/ha)
• Compact PolInSAR applications:• C-PolInSAR coherence region < F-PolInSAR coherence region• C-PolInSAR coherence region F-PolInSAR coherence region
• System implications Calibration
IGARSS 201027
Calibration of a CP system
• CP system:
• System has to be perfect before transmission because it is not possible to correct afterwards
• With a perfect transmission 4 unknowns δ1, δ2, Ω, f1
1, j
R TM A r e D R SR D Nj
1, j
RM A r e D R SR Nj
1 1
j j
2
23
1
21
2
f
fj
α ~ 1
β ~ -jδf 2~1
2 3
1 1 4 2
1 1cos sin cos sin 11,
sin cos sin cos2RH HH HV Hj
RV VH VV V
M S S NA r e
M S S Nf f j
IGARSS 201028
• Dihedral at 0°
• Dihedral at 45°
• Expansion of
• Trihedral at 0°
Calibration of a CP system
12
1
1212
11
cossinsincos
cossinsincos
2
1
fjS
jSAe
fjSfS
jSSeAeM
HV
HVj
VVHH
VVHHjj
0
0
0
0
D
D
AS
A
0
01
2 1
1DRH
DRV
M j
jfM
0
0
D
D
AS
A
1
1 2
DRHDRV
M j
M f j
0
01
1
2
DDRVRH
D DRV RH
MMm
M M
0
0
*
1 12
D DRV RV
DDRHRH
M Mje
MM
0 0
0 0
*
1 2
D D DDRV RV RVRH
D DD DRH RVRH RH
M M MMj
M MM M
D DRH RVM M
2* * *2 1 1 1 1
DRHDRV
Mf f jf
M
0
0
T
T
AS
A
1
2T DRH RHT DRV RV
jf
M MM M
*
*
2 *2 1 1 1 1
DRH
DRV
Mf f jf
M
0
0
1
ln 22
D DD TRV RVRH
T D DDRH RHRH
M MMj Aj j
M A MM
IGARSS 201029
Conclusion
• π/2 mode is required for low frequency spaceborne radar• Introduction of a parameter : the conformity coefficient
• Is FR-independent• Allows to distinguish 3 types of scattering
• Estimation of FR over bare surfaces identified by the conformity coefficient
• Compact PolSAR applications:• Estimate of soil moisture is possible over bare surfaces selected by μ and
using Dubois et al. Algorithm – RMS error of 2% over AIRSAR L-band data• Quantify biomass with HV’ (RMS error : 6,25 tons/ha) and RR (6,63 tons/ha)
instead of HV (5,8 tons/ha)• Compact PolInSAR applications:
• C-PolInSAR coherence region < F-PolInSAR coherence region• C-PolInSAR coherence region F-PolInSAR coherence region
• Calibration• Require a perfect transmission• Suggest 3 external targets to calibrate a CP system