IGARSS’11

Compact Polarimetry Potentials

My-Linh Truong-Loï, Jet Propulsion Laboratory / California Institue of Technology

Eric Pottier, IETR, UMR CNRS 6164Pascale 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

• 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

Issues

IGARSS’11

Mode Swath ResolutionIncidence

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

Background - Example with ALOS system

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,…)

• Hybrid polarity : particular case of π/2 : one circular transmission and two coherent linear polarizations in reception (H&V)

1

2

11 1

2 2HH HV HH HV

VH VV VH VV

S S S jSkk

S S S jSk j

IGARSS’11

/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)– m- method based on Stokes parameters

(1) 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.

(2) 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.

(3) 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.

(4) R. K. Raney, Hybrid-Polarity SAR Architecture, IEEE Transactions on Geoscience and Remote Sensing, vol. 45, no. 11, November 2007.

Background - Compact Polarimetry 2/2

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

Calibration – Full-pol system

• Full-pol system calibration : 7 unknowns δ1, δ2, δ3, δ4, Ω, f1, f2

• The S matrix can be recovered:

• Distorsions can be retrieved with measures over known targets:– Trihedral, dihedral, transponder, natural targets, etc.

, jR TM A r e D R SR D N

NfSS

SS

ferAM

VVHV

VHHHj

24

3

11

2 1

cossin

sincos

cossin

sincos1,

1 1 1 1R TS R D MD R

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:

• The transmission defects cannot be corrected a posteriori

• System needs to be of high quality before transmission

• With a high-quality transmission 4 unknowns 1, 2, , f1

11,

2j

R TM A r e D R SR D Nj

11,

2j

RM A r e D R SR Nj

1 1 11

2R TR D M SR D

j

IGARSS’11

• Compact polarisation– 3 reference targets are necessary

• Dihedral @ 0°• Dihedral @ 45°• Trihedral

• Full polarisation– More unknowns

– But less targets are required

– Natural targets can be used

– Acquisition of both HV and VH

12

1

1212

11

cossinsincos

cossinsincos

2

1fjS

jSAe

fjSfS

jSSeAeM

HV

HVj

VVHH

VVHHjj

00

0 0

1

ln 22

D DD TRV RVRH

D DD DRHRV RH

M MMj Aj j

A MM M

0

0

2 *2 1 1 1 1

DRH

DRV

Mf f jf

M

0 0

0 01 2

D D DDRV RV RVRH

D DD DRH RVRH RH

M M MMj

M MM M

12

T DRH RHT DRV RV

jf

M M

M M

Calibration – Compact-pol system

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

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

{R;G;B}={HH;HV;VV}, SETHI data, L-band, Garons

Example of raw data, range spectra HH

IGARSS’11

Building compact polarimetric data

HVHHRH jSSM

Processed data

Raw data

Process 1

rawHVS

proHVS

rawHHS

Processing (corrections, antenna beam, etc.)

Processing (corrections, antenna beam, etc.)

Calibration:

MRHpro

rawHHS

proHHS

propropro HVHHRH SHHA

HVAjSHHAk

_

__

Hilbert transform

Processing (corrections, antenna beam, etc.)

Calibration:

MRH

Process 2

rawHVS

rawrawraw HVHHRH SHHA

HVAjSk

_

_

rawRHRH kHHAk _

rawHVjS

rawHHS

IGARSS’11

Building CP data - Process 1 / Process 2

Image of CP data from FP raw data, {R ;G;B}={ MRh+MRv ;MRh ;MRv }

Image of CP data from FP processed data, {R ;G ;B}={ MRh_pro+MRv_pro ;MRh_pro ;MRv_pro }proRH

rawRH

MM

0 1Coherence between both images

IGARSS’11

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 P-band data over Nezer forest

(HV)

(RR) (RH)

(HV)

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

0.1274205.8 HVHVB e

0.1465178.01 HV

HVB e 0.162653.142 RR

RRB e

120 tons/ha

0

IGARSS’11

Biomass map – Nezer forest

BHV BHVBRR

120 tons/ha

0

Measured biomass

IGARSS’11

Biomass estimate with HV regression

RMS error=20.1 tons/ha

Bias=19.5 tons/ha

Using the HV regression as a reference, computation of the biomass with HV backscattering coefficient

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