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Introduction

 

Dependence of Polarimetric Surface Scattering on Spatial Resolution

Sang-Eun Park(1), Laurent FERRO-FAMIL(1), Eric POTTIER(1) and Sophie ALLAIN(1)

(1) University of Rennes 1, IETR, Bat 11D, 263 Avenue General Leclerc, 35042 RENNES, France

Abstract

The objective of this study is to understand the influence of spatial resolution on surface backscattering characteristics for high resolution polarimetric radar systems. Several studies have reported the causal relationship between surface scattering responses and the spatial resolution cell size [1-3]. Since these studies have been conducted under fixed dielectric conditions, the effect of the spatial resolution on the roughness statistics probably cause the variation of backscattering signatures. Especially, in the microwave surface scattering problem, an adequate mathematical formulation for the roughness autocovariance of the target surface is essential to obtain accurate backscattering characteristics. The actual or realistic expression of surface ACF has been an important issue, and different types of roughness autocovariance function have been proposed in literatures. Previous studies were carried out based on the infinitely long scattering surfaces. However, a radar image is acquired from a coherent summation of elementary scattering contributions within finite ground resolution. Statistical properties of random rough surfaces are affected by the spatial resolution of the radar sensor. In this study, a new expression for roughness autocovariance function of the truncated surface is proposed in order to characterize surface scattering of high resolution imaging radar. Simulation results obtained from the autocovariance function of the truncated surface show that the angular behaviors of backscattering coefficients increase with the spatial resolution. In addition, variations of the correlation length also affect backscattering coefficients. Traditional computation of the surface backscattering based on the autocovariance function of infinite surface leads to an underestimation of the radar response in case of the surfaces with a high correlation length. Furthermore, simulated polarimetric backscattering coefficients obtained from the new autocovariance function have been compared with indoor polarimetric SAR measurements acquired by the European Microwave Signature Laboratory under the Joint Research Center. The simulation results are in good agreement with the measured values which are dependent on the spatial resolution. The roughness descriptors for the truncated surface of high resolution radar are pertinent to explain the relationship between the polarimetric surface scattering and the spatial resolution.

[1] K. Sarabandi, and Y. Oh, “Effect of antenna footprint on the statistics of radar backscattering from Random Surfaces”, in Proc. IGARSS, Florence, Italy, 1995, pp. 927-929. [2] G. Nesti, J. Fortuny, and A. J. Sieber, “Comparison of backscattered signal statistics as derived from indoor scatterometric and SAR experiments”, IEEE Trans. Geosci. Remote Sensing, vol. 34, no. 5, pp 1074-1083, 1996. [3] S. Allain, L. Ferro-Famil, E. Pottier, and J. Fortuny, “Influence of resolution cell size for surface parameters retrieval from polarimetric SAR data”, in Proc. IGARSS, Toulouse, France 2003, pp. 440-442.

 

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