Page 420 - Fundamentals of Radar Signal Processing
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FIGURE 5.40 Pulse Doppler spectrum for a large RCS crossing target in weak
clutter.
The concept of clutter mapping is shown in Fig. 5.41, which presumes that
conventional pulse Doppler processing is applied to targets having Doppler
shifts sufficient to separate them from the ground clutter, i.e., those in the clear
region of the Doppler spectrum. The output of the zero-Doppler bin and others
in the clutter region is used to create a stored map of recent clutter echo power
for each range-azimuth cell in the radar’s search area. This map is updated
continuously to allow for clutter variations due to weather and other
environmental changes. On each scan, the received power in the clear region
Doppler bins is applied to a conventional threshold detector using a threshold
based on the noise that dominates the interference in those bins. Instead of being
discarded, the current received power in the clutter region Doppler bins for
each range-azimuth cell is applied to a separate detector using a threshold based
on the stored clutter power level for that cell. The clutter map procedure is a
form of constant false alarm rate (CFAR) detection but with the interference
power estimated by averaging in time instead of in space. The details of
threshold detection and CFAR are discussed in Chap. 6
