Comparative evaluation of the sensitivity of multi-polarized multi-frequency SAR backscatter to plant density

Interaction of synthetic aperture radar (SAR) with vegetation is volumetric in nature, hence SAR is sensitive to the variation in vegetation density. At the same time SAR is also sensitive to other target properties such as canopy structure, canopy moisture, soil moisture and surface roughness of the underlying soil. However, the sensitivity of SAR backscatter to the vegetation density depends upon the frequency, polarization and angle of incidence at which the SAR is operated. This paper provides comparative evaluation of the sensitivity of multi-frequency and multi-polarized SAR backscatter to the plant density of Prosopis juliflora, a thorny plant. Monitoring of P. juliflora is of importance as the state forest department introduced it to arrest the spread of desert. In carrying out this study, data from the SIR-C/X-SAR mission over parts of Gujarat, India, have been used. In the present study, the variation of multi-frequency ( L and C) and multi-polarized (HH, VV and VH) SAR backscatter with plant density has been studied. The results clearly indicate that cross-polarized SAR backscatter at longer wavelength is the appropriate choice for the quantitative retrieval of plant density.