Modeling of microwave bistaic scattering from a rice canopy

Numerous works show the great potential of microwave remote sensing in assessing biophysical variables of rice plants. However, most studies are focusing on the backscattering character of rice canopy. Much lesser attention has been devoted to modeling bistatic scattering behavior of rice canopy. Therefore, this study aims to improve the understanding of bistatic scattering response of rice canopy, and thus help design a bistatic radar system for better monitoring rice growth and yield estimation. Firstly, a bistatic scattering of a cluster of rice plant was modelled by solving the vector radiative transfer equations up to the second order. For a rice canopy within the antenna footprint, the total scattered field is a coherent sum of scattered fields from all the clusters that are practiced into a two-dimensional quasi-periodic setting. In this study, the concept of antenna array is applied to account for the inter-cluster wave interactions to obtain the total scattered field and bistatic scattering coefficient The developed scattering model is validated by extensive comparisons with in-situ measurements from various regions. Then, the bistatic scattering characteristics of rice canopy was examined by identifying the frequency responses and angular dependence of rice eco-physiological properties. The results show that bistatic scattering coefficient varies greatly over different growth stages, and is strongly dependent on rice plants' structure, including the size, shape, and orientation, especially stems. In addition, the dynamic range of bistatic scattering coefficient can be substantially expanded compared to that of the backscattering coefficient. The model sensitivity will be discussed in regard of the rice canopy parameters retrieval.