Electromagnetic scattering from grassland. I. A fully phase-coherent scattering model

A microwave scattering formulation is presented for grassland and other short vegetation canopies. The fact that the constituent elements of these targets can be as large as the vegetation layer make this formulation problematic. For example, a grass element may extend from the soil surface to the top of the canopy, and thus the upper portion of the element can be illuminated with far greater energy than the bottom. By modeling the long, thin elements of this type of vegetation as line dipole elements, this nonuniform illumination can be accounted for. Additionally, the stature and structure of grass plants can result in situations where the average inner-product of coherent terms are significant at lower frequencies. As a result, the backscattering coefficient cannot be modeled simply as the incoherent addition of the power from each element and scattering mechanism. To determine these coherent terms, a coherent model that considers scattered fields, and not power, is provided. This formulation is then used to provide a solution to the multiple coherent scattering terms, terms which include the correlation of the scattering between both dissimilar constituent elements and dissimilar scattering mechanisms. Finally, a major component of the grass family are cultural grasses, such as wheat and barley. This vegetation is often planted in row structures, a periodic organization that can likewise result in significant coherent scattering effects, depending on the frequency and illumination pattern. Therefore, a formulation is also provided that accounts for the unique scattering of these structures.