Page 38 - Fundamentals of Radar Signal Processing

FIGURE 1.1 Spherical coordinate system for radar measurements.

Because most people are familiar with the idea of following the movement
of a “blip” on the radar screen, detection and tracking are the functions most
commonly associated with radar. Increasingly, however, radars are being used
to generate two-dimensional images of an area. Such images can be analyzed for
intelligence and surveillance purposes, for topology mapping, or for analysis of
earth resources issues such as mapping, land use, ice cover analysis,

deforestation monitoring, and so forth. They can also be used for “terrain
following” navigation by correlating measured imagery with stored maps. While
radar images have not achieved the resolution of optical images, the very low
attenuation of electromagnetic waves at microwave frequencies gives radar the
important advantage of “seeing” through clouds, fog, and precipitation very
well. Consequently, imaging radars generate useful imagery when optical
instruments cannot be used at all.

The quality of a radar system is quantified with a variety of figures of
merit, depending on the function being considered. In analyzing detection
performance, the fundamental parameters are the probability of detection P D
and the probability of false alarm P . If other system parameters are fixed,
FA
increasing P always requires accepting a higher P as well. The achievable
FA
D
combinations are determined by the signal and interference statistics, especially
the signal-to-interference ratio (SIR). When multiple targets are present in the
radar field of view, additional considerations of resolution and sidelobes arise
in evaluating detection performance. For example, if two targets cannot be
resolved by a radar, they will be registered as a single object. If sidelobes are
high, the echo from one strongly reflecting target may mask the echo from a
nearby but weaker target, so that again only one target is registered when two