Modeling polarization properties of emission from soil covered with vegetation

Polarization characteristics of centimetric microwave emission from canopy-covered fields are investigated. Experimental data are compared against theoretical predictions obtained by two different models. In a simple and direct approach, vegetation is considered as a uniform absorbing and scattering slab with plane parallel boundaries, while in a more realistic description, plants are modeled as an ensemble of lossy dielectric disks and thin cylinders (needles). A parametric analysis, carried out to assess the sensitivity of the polarization index (PI) to the most significant parameters of vegetation shows that, although the PI is mainly influenced by global parameters such as leaf area index and plant water content, morphological parameters such as disk or needle dimensions and orientation distribution may play a relevant role. In particular, a model composed of a mixture of disks and needles is able to represent the negative value of PI sometimes measured over fully grown vegetation. >