| In this study results obtained from a series of X-band, vertically polarized, high-resolution radar backscatter measurements for winter wheat, soybeans and corn are discussed. The experimentally observed radar backscatter data indicate that leaves are the dominant scatterers for corn and soybeans. Although the scattering properties of the individual leaf have been studied, it is usually modeled as a homogeneous disk. As the leaf's ribs usually have a higher dielectric constant than the leaf surface, a theoretical investigation of the effects of dielectric inhomogeneity on the scattering behaviors of a dielectric disk was also performed here.; For winter wheat it was found that, at the early stages of heading, the heads are highly moist and lossy. As a consequence, they dominate the radar signal. At the late growth stage, as the heads become drier and cause almost no loss to the penetrating radar signal, ground returns dominate. For soybeans, leaves are the dominant scatterers at 30(DEGREES), while the stalks could be more dominant at 50(DEGREES). Under natural conditions soybeans were very lossy, so the upper 30-cm portions of the plants are the main contributors to the radar signal. For corn, the leaves are the single dominant source of scattering at all angles. For the entire canopy, the radar signal is contributed mainly by the leaves in the upper 1 - 1.5 m portion of the plants.; It is shown that, in contrast to the well-defined RCS pattern observed for a homogeneous disk, the RCS pattern of the inhomogeneous disk exhibits shallow nulls and high sidelobes (especially for the HH-polarization case at near grazing incidences). The above observations suggest that the rib has significant effects on the scattering behaviors of a leaf and, therefore, should be taken into account (in addition to a knowledge of the sources of scattering for various vegetation canopies) while developing a backscatter model for a vegetation canopy. |
