Compact Polarimetry Potentials

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Compact Polarimetry Potentials

• My-Linh Truong-Loï, Jet Propulsion Laboratory /
  California Institue of Technology
• Eric Pottier, IETR, UMR CNRS 6164
• Pascale Dubois-Fernandez, ONERA

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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

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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

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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

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Background - Compact Polarimetry 1/2

• p/4 mode one transmission at 45 and two
  coherent polarizations in reception (linear H
  V, circular right left,)
• p/2 mode one circular transmission and two
  coherent polarizations in reception (linear H
  V, circular right left,)
• Hybrid polarity particular case of p/2 one
  circular transmission and two coherent linear
  polarizations in reception (HV)

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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)
• m-d 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.

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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

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Calibration Full-pol system

• Full-pol system calibration 7 unknowns d1,
  d2, d3, d4, O, f1, f2
• The S matrix can be recovered
• 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.
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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 d1,
  d2, ?, f1

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Calibration Compact-pol system

• Compact polarisation
• 3 reference targets are necessary
• Dihedral _at_ 0
• Dihedral _at_ 45
• Trihedral
• Full polarisation
• More unknowns
• But less targets are required
• Natural targets can be used
• Acquisition of both HV and VH

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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

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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
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Building compact polarimetric data
Raw data
Processed data
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Building CP data - Process 1 / Process 2
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Compact-pol - Process 2 / Process 2
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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

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Backscattering coefficients and biomass RAMSES
P-band data over Nezer forest
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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)
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Biomass map Nezer forest
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Biomass map Nezer forest
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Biomass estimate with HV regression
Using the HV regression as a reference,
computation of the biomass with HV backscattering
coefficient
RMS error20.1 tons/ha Bias19.5 tons/ha
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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

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Thank you for your attention