Abstract
In the microwave remote sensing of a vegetation canopy over a flat ground, the vegetation-ground interaction scatter can become large. For such a case, the traditional theories used to explain the radar signatures, that is, the fiist order vector transport theory and the distorted Born approximation (DBA), differ in the backscatter direction. This difference, known as the backscattering enhancement effect, is due to the coherent interaction between forward and reverse going ground-vegetation interaction scatter and is accounted for by the field-based DBA but not by the transport theory, which is basically an incoherent theory. At some point away from the backscatter direction, the two theories agree, This means that the enhancement effect has a fiiite width associated wi$ it. This enhancement width, ranging anywhere from 1/2O to 20' for practical microwave frequencies, depends on the frequency and the vegetation layer thickness, and can be an important factor when measuring soil moisture and its sensitivity. This is because if the enhancement width is small relative to the receiving antenna beamwidth, the effect will not likely be seen. Such a case occurs for C-band remote sensing using a ground-based radar system with antenna beamwidths of over 10. On the other hand, if the enhancement width is large relative to the receiving antenna beamwidth, the effect will likely be seen. Such a case occurs for L-band remote sensing using an airborne SAR system with antenna beamwidths of less than 1. Thus, the theory (either DBA or transport) used in the modeling procedure will depend to a large extent on the type of radar system being used.
Published Version
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