Power spectrum of wind-influenced vegetation backscatter at x-band

The baseband power spectral density characteristics of X-band radar backscatter from wind-influenced vegetation were investigated using a short-range continuous wave radar system. Radar reflectance and concurrent windspeed data were gathered from various individual trees from a distance of approximately 30 m. The power spectral density was observed to drop off at a rate slower than the widely-used single-peak Gaussian model. An empirical model which characterises the power spectrum as a combination of Gaussian functions with different peak locations is proposed. The model postulates that (i) the spectral broadening of the central peak is attributable to branch sway, (ii) the location of non-central peaks is attributable to leaf flutter, and (iii) the spectral broadening of the non-central peaks is attributable to a combination of branch sway and leaf flutter. The model shows satisfactory agreement with measured data. It is shown that realistic estimates of MTI improvement factors for delay-line cancellers can be obtained by knowledge of the type of vegetative clutter environment.