TABLE OF CONTENTS The radar equations and the statistics of detection described in the previous chapters were based on the return signal from a target exceeding a fixed threshold. It was assumed that this threshold was established with respect to either the rms value of the system noise or the environmental noise prior to searching for the target. [1] In the typical surface-radar situation, environmental effects or electronic counter-measures make that assumption of limited value. Figure 4.1 shows, in an overly simplified way, the effects of the range dependence of the mean radar backscatter from various types of clutter at a transmit frequency of 3000 MHz (S-band). In this figure backscatter is normalized to the radar cross section of a target at a given range (left-hand ordinate); the right-hand ordinate is an estimate of the radar cross section of a target that can be detected in the presence of the clutter at the corresponding range. The required target signal-to-clutter ratio is assumed to be 20 to 1 (13 dB). This is a typical value for a narrow-beam surveillance radar. The purpose of this plot is to illustrate that:
The various types of radar clutter have different range dependencies and considerable time variations of intensity (rainfall rate, chaff density, sea state).
For the chosen parameters of the radar, the clutter effects exceed the receiver noise by several orders of magnitude.
The radar cross section of rural clutter is comparable to that of small aircraft (1 to 10 m 2) and...
