Overview

After the signals have been filtered to exclude out-of-band noise, the pulse has been compressed (when necessary), and the clutter and interference have been reduced to the noise level, a decision is made as to whether the echo signal represents an object of interest. The decision may be made automatically or by an operator.

For radars that observe ground areas for moving objects, a gate may be set over the echo of interest and the operator is able to listen to the signal using earphones. Each type of animal, human, and vehicle gives its characteristic "music", which a trained operator is able to identify.

Most scatterers are irregular, and their fluctuation or fading characteristics have been described in Chapter 6 (Factors outside the radar). This chapter describes the probabilities of detection of five of the classical cases.

This chapter deals with the statistics of signals and noise giving the probabilities of:

• Random noise impulses adding together and by chance having the characteristics of a valid echo signal, the probability of false alarm, P _fa;

• A wanted echo being recognized as such, or the probability of detection.

Basic gamma distributions are used in this chapter in place of Pearson's form of the incomplete gamma distribution and the chi-square distribution for which there are tables as used by older texts. Modern computers are able to calculate Bessel and gamma functions and their integrals directly.

Fourier transforms, described in Chapters 15 and 16, are used to calculate the probability density functions...