In this paper, we provide a review of the different approaches used for target decomposition theory in radar polarimetry. We classify three main types of theorem; those based on the Mueller matrix and Stokes vector, those using an eigenvector analysis of the covariance or coherency matrix, and those employing coherent decomposition of the scattering matrix. We unify the formulation of these different approaches using transformation theory and an eigenvector analysis. We show how special forms of these decompositions apply for the important case of backscatter from terrain with generic symmetries.

A review of target decomposition theorems in radar polarimetry

The authors examine the role of polarimetry in synthetic aperture radar (SAR) interferometry. They first propose a general formulation for vector wave interferometry that includes conventional scalar interferometry as a special case. Then, they show how polarimetric basis transformations can be introduced into SAR interferometry and applied to form interferograms between all possible linear combinations of polarization states. This allows them to reveal the strong polarization dependency of the interferometric coherence. They then solve the coherence optimization problem involving maximization of interferometric coherence and formulate a new coherent decomposition for polarimetric SAR interferometry that allows the separation of the effective phase centers of different scattering mechanisms. A simplified stochastic scattering model for an elevated forest canopy is introduced to demonstrate the effectiveness of the proposed algorithms. In this way, they demonstrate the importance of wave polarization for the physical interpretation of SAR interferograms. They investigate the potential of polarimetric SAR interferometry using results from the evaluation of fully polarimetric interferometric shuttle imaging radar (SIR)-C/X-SAR data collected during October 8-9, 1994, over the SE Baikal Lake Selenga delta region of Buriatia, Southeast Siberia, Russia.

Polarimetric SAR interferometry

In this paper, we examine the role of polarimetry in synthetic aperture radar (SAR) interferometry. We first propose a general formulation for vector wave interferometry that includes conventional scalar interferometry as a special case. Then, we show how polarimetric basis transformations can be introduced into SAR interferometry and applied to form interferograms between all possible linear combinations of polarization states. This allows us to reveal the strong polarization dependency of the interferometric coherence. We then solve the coherence optimization problem involving maximization of interferometric coherence and formulate a new coherent decomposition for polarimetric SAR interferometry that allows the separation of the effective phase centers of different scattering mechanisms. A simplified stochastic scattering model for an elevated forest canopy is introduced to demonstrate the effectiveness of the proposed algorithms. In this way, we demonstrate the importance of wave polarization for the physical interpretation of SAR interferograms. We investigate the potential of polarimetric SAR interferometry using results from the evaluation of fully polarimetric interferometric shuttle imaging radar (SIR)-C/X-SAR data collected during October 8-9, 1994, over the SE Baikal Lake Selenga delta region of Buriatia, Southeast Siberia, Russia.

The Kennaugh-Huynen scattering matrix con-diagonalization is projected into the Pauli basis to derive a new scattering vector model for the representation of coherent target scattering. This model permits a polarization basis invariant representation of coherent target scattering in terms of five independent target parameters, the magnitude and phase of the symmetric scattering type introduced in this paper, and the maximum polarization parameters (orientation, helicity, and maximum return). The new scattering vector model served for the assessment of the Cloude-Pottier incoherent target decomposition. Whereas the Cloude-Pottier scattering type alpha and entropy H are roll invariant, beta and the so-called target-phase parameters do depend on the target orientation angle for asymmetric scattering. The scattering vector model is then used as the basis for the development of new coherent and incoherent target decompositions in terms of unique and roll-invariant target parameters. It is shown that both the phase and magnitude of the symmetric scattering type should be used for an unambiguous description of symmetric target scattering. Target helicity is required for the assessment of the symmetry-asymmetry nature of target scattering. The symmetric scattering type phase is shown to be very promising for wetland classification in particular, using polarimetric Convair-580 synthetic aperture radar data collected over the Ramsar Mer Bleue wetland site to the east of Ottawa, Ontario, Canada

https://www.pcigeomatics.com/pdf/whitepapers/Touzi_target_scattering.pdf

Target Scattering Decomposition in Terms of Roll-Invariant Target Parameters

Polarization, together with the amplitude, time, frequency, phase, and bearing descriptors of radar signals, completes the information which can be obtained on target returns in monostatic radars. The exploitation of information on the echo polarization state through polarimetric radars is currently a subject of interest, due to theoretical and technological advances, as well as to the development of new radar applications. Many polarization techniques, which have been proposed and analyzed to enhance radar performance, are reviewed in this paper in order to assess the possible improvement they can provide in the signal-to-disturbance ratio, target detectability, target discrimination and resolution, and target classification and identification. Some recent experimentally based results relating to these applications are also presented. Those techniques are emphasized for which polarization-based capabilities appear sufficiently assessed, such as adaptive polarization cancellation of clutter, chaff, and jamming. Polarization Doppler processing of dual-polarization radar signals, meteorologic applications, and polarization adaptation for target detection in the clear (in free space) are also examined.

Polarization diversity in radars

The complete description of electromagnetic scattering processes implies polarization since an electromagnetic scatterer acts like a polarization transformer. The main objective is to show that due to the vector nature of electromagnetic waves, electromagnetic remote sensing and inverse scattering techniques, if applied rigorously, require incorporation of polarization information into their formulation. By applying this approach to existing and some novel theories, remarkable improvements in quality and fidelity of the reconstructed profiles and/or images can be obtained. Thus there is ample justification for continuing efforts in developing methods and theories of vector inverse scattering for the electromagnetic polarization-dependent case or in the even more complicated seismic case of p - and s -wave interaction in elastic media as for example encountered in vertical seismic profiling.

M. El-Arini

Papers

Polarization dependence in electromagnetic inverse problems