Page 137 - Fundamentals of Radar Signal Processing

tree leaves moving in the wind or waves on the sea surface, and by changes in

radar-target geometry for both clutter and targets. Various investigators have
experimentally characterized the decorrelation characteristics of clutter echoes
due to internal motion, or equivalently, their power spectrum. For example, one
model suggested to estimate the power spectrum of the RCS of foliated trees or
rain uses a cubic spectrum (Currie, 2010):

(2.67)

The corner frequency F is a function of the wavelength and either wind
c
speed (for trees) or rain rate (for rain). Some sample measured values are given
i n Table 2.7. A higher corner frequency (wider power spectrum) implies a
shorter decorrelation interval (narrower autocorrelation function). Shorter
decorrelation times render the clutter signals more like white noise and degrade
the effectiveness of some of the clutter suppression techniques of Chap. 5.
Notice that for a given weather condition, the clutter decorrelates more rapidly
at higher radar frequencies. Figure 2.23 plots additional windblown tree clutter

data that also show the decrease in decorrelation time for both increased clutter
motion and increased radar frequency.

Source: Currie, N. C. “Clutter Characteristics and Effects,” chapter 10 in J. L. Eaves and K. E. Reedy
(eds.), Principles of Modern Radar. Van Nostrand Reinhold, New York, 1987.

TABLE 2.7 Cubic Power Spectrum Corner Frequencies (Hz) for Rain and Tree
Clutter