Electromagnetic scattering from short branching vegetation

A polarimetric coherent electromagnetic scattering model for short branching vegetation is developed in this paper. With the realistic structures that reasonably describe the relative positions of the particles, this model is able to consider the coherent effect due to the phase difference between the scattered fields from different particles, and account for the second-order, near-field interaction between particles, to which the relative positions and orientation of the particles are essential. The model validation with measurements is also presented, and excellent agreement is obtained. The polarimetric radar backscatter measurements for soybean plants using truck-mounted scatterometers were conducted at L-band and C-band under different soil-moisture conditions. Through an extensive ground truth, the important plant and rough surface parameters such as the soil moisture and surface roughness, vegetation dielectric constant, and geometry of the soybean plants, were characterized for model verification. It is found that the second-order near-field scattering is significant at C-band for fully grown soybeans due to the high vegetation particle density, and at L-band, the contribution from the second-order near field is negligible. The coherence effect is shown to be important at L-band and to a much lesser extent at C-band. This model is then used to demonstrate its ability for estimating the physical parameters of a soybean field, including soil moisture from a polarimetric set of AIRSAR images.