compact versus full polarimetric sarearth.esa.int/workshops/polinsar2009/participants/525/... ·...

Canada Centre for Remote Sensing • Earth Sciences Sector

1R. Touzi, CCRS, Frascatti, Pol-InSAR 2009

R. Touzi

Canada Centre for Remote Sensing

Compact Versus Full Polarimetric SAR



Background

Full polarimetry requires doubling the PRF => half of the swathCompact (or hybrid) -dual polarization old technology 1960) rescucited (Souyris 05, Raney 07)

Missing message: Cheap way to do polarimetry at full swath!!!!

Compact versus Polarimetry ????

Compact versus dual polarization HH-HV, VV-VH?

Hybrid full polarimetry versus HH, HV, VH, VV ??



Compact & Hybrid

• Dual-Polarization (DP):1. Linear DP: HH-HV or VV-VH

2. Compact:– Transmitted polarization: H+V (π/4) or CP (hybrid)– Received polarization: H and V

Circular Polarization (CP): RR-RL

• Full-Polarimetry (FP):1. Linear FP: HH-HV-VV-VH

2. Hybrid FP: RH-RV-LH-LV



OUTLINE

HV measurement using Compact-Hybrid versus Linear DP

Compact Versus Polarimetry:

Wave Poincaré Sphere parameters: Degree of polarization and cross-channel coherence phase

Target Poincaré Sphere parameters: symmetric scattering type phase and magnitude (αs , Φαs ), and helicity (τ)

Compact Versus Polarimetry: What do we get???

What do we miss???



Fully Polarimetric System Design

Fundamental data reception strategies (Livingstone):1. All data are time multiplexed through a single receiver

(ESAR, DLR)

2. Two parallel receiver channels; each receiver is dedicated to one receiving antenna polarization (AIRSAR, SIRC)

3. Two parallel receiver channels; one receiver is assigned to HH-VV, and the second to HV-VH (CV580, Livingstone 1989)

R. Touzi, C.E. Livingstone, et al., Antenna Gain and Phase Patterns for Calibration of Polarimetric SAR Data; IEEE TGRS, 31, 6, 1993



Convair-580 Polarimetric SAR

HH and VV larger than HV and VH (6 dB)

LNA well beyond the receiver

(HV-VH)- S/N increased of 6 dB

HV and VH averaged => +3 dBincrease => (K. Raney TGRS 1988)



HV Measurement: Hybrid versus Linear FP

• Hybrid FP:– Received HH + jHV and VV + jVH– HH generally higher than HV: (6 dB) for azimuthally symmetric targets– Receiver of limited bandwidth

HH of higher values while HV of low signal missedHV of low signal while HH of large values missed

• Linear FP:– HH-VV and HV-VH in separate receivers

– LNA to increase HV-VH of 6 dB in S/N

Hybrid versus Linear: – Linear FP => HV of better S/N – Hybrid: Large incidence angles (range ambiguities Raney&

Freeman)



Compact Verus FPHV Reconstruction from Compact

• Compact an estimate of FP

HV reconstructed from Compact (J.C. SouyrisTGRS 2005)

Radiometric calibration error (3-6 dB)



HV reconstruction from CompactJ.C. Souyris 2005

• Reflection symmetry: <hh.hv*> = 0 = <vv.vh*>

• X= <|hv|2>, H=<|hh|2>,V=<|vv|2>, P= <hh.vv*>

• Iterative method to estimate <|hv|2> under the condition:

Estimate of FP covariance =>

[ ] ⎥⎦

⎤⎢⎣

⎡++++

≅XVXPXPXH

J *4/π

[ ]⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

−−

−−≅

XjXjX

XjXjC FP

22*

12

1211

0020

0ˆ

4/)1( *hhvvVHX ρ−≅+



HV reconstruction from Compact



HV reconstruction from Compact3-6 dB Error

<|hv|2> reconstructed not reliableMarsh dipole scattering of <|hv|2> very bright like for HH



HV Measurement: Dual: Compact versus Linear (HH-HV)

• Full Polarimetric versus dual-Compact– HV reconstructed (J.C. Souyris)– Radiometric calibration error (3-6 dB)

Dual linear versus Compact: HH-HV if the Client requires calibrated HV

High Faraday conditions RR-RL or RH-RV

Radiometry preserved even though the phase difference RR-RL not calibrated for Faraday rotation



Representation of Polarization for partially polarized waves: Poincare Sphere

• Degree of polarization:

• δ: Phase(EHEV*)

Hybrid equivalent to CP

⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢

⎣

⎡

==

>−=<

>+=<

=

)Im(2)Re(2

*3

*2

221

220

VH

VH

VH

VH

HV

EEsEEs

EEsEEs

Sr

0

23

22

21

ssss

p++

=

RLHV SSrr⋅

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

=

0010100001000001



Wetland Classification: RAMSAR Mer Bleu SiteConvair-580 SAR HH (red), HV (green), VV (bleue)

MarshSedge-Fen

Treed bogShrub bog

Treed Bog



Full Polarimetric C-band SARScattering Phase (Touzi Decomposition)

Tree BogFenShrub BogMarshUpland forest

Mer Bleue wetland classification Based on the NCC forest cover inventory



RH-RV Coherence PhaseVersus FP scattering phase


1. Conifer treed bog ≅ upland deciduous forests

2. Bog ≅ poor fen

3. Marsh



RH-RV Coherence PhaseVersus HH polarization

1. Conifer treed bog ≅ upland deciduous forests

2. Bog ≅ poor fen

3. Marsh



Wave polarization information

Wave Poincaré sphere parameters depend on the polarization of transmitting antenna

Transmitted polarization that optimizes scattered wave parameters

Methods for optimisation of scattered wave parameters:

Completely polarized wave extrema (Kostinski-Boerner 86)

Poelman multinock filter (Poleman 76)

Contrast optimization of partially coherent targets (Swartz 88)

Extrema of the degree of polarization & scattered wave intensity(Touzi 92)

Degree of Polarization signature (Degrandi 94)



What we Get? What we Miss ?



Hybrid versus FP polarization degree



Extrema of the scattered wave degree of polarization: the Touzi Anisotropy

• The Von Neumann Entropy Measure:

– [J]: coherence matrix of the scattered wave

– p : degree of polarization

The Touzi Anisotropy ΔH

R. Touzi. Calibrated Polarimetric SAR data for ship detection, IGARSS’00 , Hawaii, 2000

Touzi et al., Ship detection and characterization using Polarimetric SAR. CJRS, Vol. 30, No. 3, pp. 552–559, 2004.

[ ]( ) [ ] [ ]( )( )JJtrJH ln•−= [ ]( ) [ ]( ) ( ){ }psJtrFuncJH ,=

( ) ( ) 21

21

11)( 21

pp

ppps−+

−+=



The Touzi Anisotropy

• The total intensity of the scattered wave Ro = tr([J]) varies with the polarization of the transmitting antenna

• The degree of polarization p varies with the polarization of thetransmitting antenna

Entropy H varies with the polarization of the transmitting antenna

Touzi Anisotropy: ΔH => measure of target scattering complexity

The more the target is structured the higher is ΔH

Dynamic range of the entropy: ΔH



Polarimetric C-band SAR for Ship detection

Radarsat1 HH-Polarization Touzi-Anisotropy



Ships-Sea Contrast (in dB)

0

5

10

15

20

25

30

40 45 50 55 60 65 70

Incidence Angle (Degree)

dB

HH

HV

VV

RR

Ent. Var.

Ship-Sea Contrast

05

1015202530

20 30 40 50 60 70

Incidence Angle

dBHHHVVVEnt



Scattering type parameters using Compact reconstructed FP

Miss-leading: surface scattering Dipole scattering φ αs meaningless, ψ=0, τ=0



Compact φ αs meaningless



Color aerial photographs(2002) overlaid with a wetland classification based on the NCC the forest cover inventory.

What You Miss???Dominant scattering Type Phase Φαs1

for Wetland Classification




What You Miss???Asymmetry (τ) for Leaf-on Leaf-off

June October



Phis2

Psi1

Brook Classification

Polarimetric ALOSWapusk Park

tau2

Lichen melt pond bog

Sedge rich Fen

Lichen spruce bog

What You Miss???



Conclusions

Hybrid versus Linear: – Linear FP => HV of better S/N – Hybrid: at large incidence angles (range ambiguities

Raney& Freeman)Dual linear versus hybrid:

HV reconstructed not reliable

HH-HV when application requires calibrated HV

High Faraday conditions RR-RL or RH-RV

Radiometry preserved even though the phase difference RR-RL not calibrated for Faraday rotation



Conclusions

Compact versus Full polarimetry:

Degree of polarization for only one transmitted polarization (RCP)Wave polarization information not fully exploitedOptimum theory cannot be exploited (optimum completely polarized, optimum degree of polarization, .. Etc)

HV not well reconstructed

Scattering type parameters cannot be exploited

compact versus full polarimetric sarearth.esa.int/workshops/polinsar2009/participants/525/... ·...

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