The dependence of the PolInSAR degree of coherence on forest parameters

Marco Lavalle, Domenico Solimini, Eric Pottier, Yves-Louis Desnos

Abstract

Modeling backscattering from natural targets is a challenging task in the simulation of Synthetic Aperture Radar (SAR) polarimetric and interferometric images. A promising application of PolInSAR is the estimate of tree height of forests. To this end, the availability of a reliable reference model for the PolInSAR observables is crucial: first, the model can be used to identify the biophysical parameters that have more impact on the observables; second, a parametric analysis helps to design an efficient inversion approach. The degree of interferometric coherence between a pair of polarimetric SAR images (PolInSAR) is an observable of major importance for forest parameters retrieval.

The prediction of the PolInSAR coherence of forest stands has been addressed by two approaches. The first is the Random Volume over Ground (RVoG) model, which combines incoherently the ground contribution with a random canopy contribution. The model is based on four input parameters: tree height, mean canopy extinction, ground-to-volume amplitude ratio and ground topography. The second approach simulates PolInSAR images by modeling the observed surface, including forest, bare soil and grass. The ESA toolbox PolSARPro provides this simulator that coherently adds the direct contributions from vegetation and soil, the one from the ground-vegetation interaction and that from the ground-vegetation-ground interaction, both for forest and grass. The input parameters are derived from the forest characteristics, the soil surface and the SAR parameters and acquisition geometry.

We have studied the dependence of the complex coherence on the scene parameters, in particular on tree height and density and on terrain slope. Different incidence angles and frequencies (L-band and P-band) have been also considered. We first compute the total backscattering and show the results for the main polarization states and in terms of regions in the complex coherence plane. Second, we consider only the direct contribution from the vegetation and the one from the soil. The comparison of this simulation with the single contributions of the RVoG model turns out particularly useful, since on one side it provides guidelines to improve the RVoG model or to design new coherence models and, on the other, it is a basis for a new inversion procedure that will be illustrated as a further step of our work

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Index Terms—PolInSAR. Interferometry. Coherence. Forest. PolSARPro

POLinSAR 2009, the 4th International Workshop on Science and Applications of SAR Polarimetry and Polarimetric Interferometry, ESA/ESRIN, Frascati, Italy, 26-30 January 2009.

© Authors, 2009

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