Page 440 - Fundamentals of Radar Signal Processing

CHAPTER 6

Detection Fundamentals

As was noted in Chap. 1, the primary functions to be carried out by a radar
signal processor are detection, tracking, and imaging. In this chapter, the
concern is detection. In radar, this means deciding whether a given radar
measurement is the result of an echo from a target or simply represents the
effects of interference. If it is decided that the measurement indicates the
presence of a target further processing is usually undertaken. This additional

processing might, for instance, take the form of tracking via precise range, angle,
or Doppler measurements.
Detection decisions can be applied to signals present at various stages of
the radar signal processing, from raw echoes to heavily preprocessed data such
as Doppler spectra or even synthetic aperture radar images. In the simplest case,
each range bin (fast-time sample) for each pulse can be individually tested to

decide if a target is present at the range corresponding to the range bin, and the
spatial angles corresponding to the antenna pointing direction for that pulse.
Since the number of range bins can be in the hundreds or even thousands and
pulse repetition frequencies can range from a few kilohertz to tens or hundreds
of kilohertz, the radar can be making many thousands to millions of detection
decisions per second.
It was seen in Chap. 2 that both the interference and the echoes from

complex targets are best described by statistical signal models. Consequently,
the process of deciding whether or not a measurement represents the influence
of a target or only interference is a problem in statistical hypothesis testing. In
this chapter, it will be shown how this basic decision strategy leads to the
concept of threshold testing as the most common detection logic in radar.

Performance curves will be derived for the most basic signal and interference
models.
Clutter (echoes from the ground) is sometimes interference and sometimes
the target. If one is trying to detect a moving vehicle, ground clutter, along with
noise and possibly jamming, is the interference; but if one is trying to image a
region of the earth, this same terrain becomes the desired target and only noise
and jamming are the interference.
An excellent concise reference for modern detection theory is given in

Chap. 5 of Johnson and Dudgeon (1993). When greater depth is needed, another
excellent modern reference with a digital signal processing point of view is Kay
(1998). An important classical textbook in detection theory is Van Trees (1968),
while Meyer and Mayer (1973) provide a classical in-depth analysis and many
detection curves specifically for radar applications.