The present paper studies the characteristics of electromagnetic scattering from vegetation models constructed as random wire structures for the purpose of PolSAR imaging and ground surface cover recognition and classification. Radar vegetation index (RVI) has been developed for the purpose of vegetation growth monitoring. Anew method is proposed to use the RVI as an accurate monitor for the natural grassland height taking into account the operational parameters such as the PolSAR look angle and the operating frequency. Also, the present paper addresses a problem that may lead to false indications of the RVI measured for grassland areas. It frequently occurs that some of the narrow long leaves of the grass cloud are quasi-parallel and of nearly equal lengths leading to the generation of internally resonant modes. The enhancement or diminishing of the backscattered field at such internal resonances may give false indication of the RVI and, hence, wrong information can be estimated such as the water content and the grass height. A new method is proposed to model the natural grasslands as clouds of electrically conductive random curly strips for the purpose of obtaining the backscatter coefficients and, hence, the corresponding RVI. The error in height estimation using the proposed method due to the existence of the internal resonances is numerically investigated.
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