Radiative transfer theory for passive microwave remote sensing of a two-layer random medium with cylindrical structures

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Abstract
In passive microwave remote sensing of earth terrain, the application of the radiative transfer theory to the model of random medium has been used in the interpretation of various experimental data. For vegetation fields with cylindrical structures, we model the vegetation layer as a two‐layer random medium with a small correlation length lρ in the horizontal direction, and a large correlation length lz in the vertical direction. The closed form solutions for the brightness temperatures are obtained as lz approaches infinity. Using this model, the kernels in the scattering terms of the radiative transfer equations give rise to delta functions, indicating that forward scattering is dominant over all the other directions. For the case that lz is only a few wavelengths long, we find the first‐order solution with an iterative method. The results are compared with that obtained using the Gaussian quadrature method to solve the radiative transfer equations numerically. We also apply this model to match experimental data collected from corn fields.