Page 110 - Radar Technology Encyclopedia

100 COVERAGE, radar COVERAGE, radar

COVERAGE, radar. Radar coverage is the general term for
the three-dimensional boundary describing the volume in
space within which radar operational capabilities meet the
specified requirements. These requirements depend on the
type of radar and can be described in terms of detection and
false-alarm probabilities if the task is detection only. For
detection and tracking tasks, resolution and errors in measure-
ment are added to the requirements, while for target recogni-
tion the probabilities of correct and incorrect classification
become important.
The volumetric coverage of a given radar can be
described in terms of its maximum (and minimum) detection
ranges as a function of target azimuth and elevation angle, if
the detection criteria and the environment are adequately
specified. For doppler-measuring (CW, MTI, and PD) radars, Figure C49 2D search radar coverage (from Barton, 1993,
“coverage” also includes the range of target radial velocities Fig. 2.36, p. 69).
over which the radar can detect and process target data.
Required detection criteria include probability of detection P d
(per scan or cumulative), probability of false alarm P , or
fa
false-alarm time t per scan, target radial velocity, target
fa
radar cross section s, and statistical RCS fluctuation model
assumed. For comparing the performance of different radar
designs for the same mission, it is common practice to assume
a standard set of detection criteria (e.g., for a volume search
2
- 6
radar, P = 0.5 to 0.9, P = 10 , s = 1 m , Swerling case 1
d
fa
fluctuation model) and a standard environment, such as free-
space.
The graphical representation of coverage is called a cov-
erage chart (or diagram). A complete description of radar
coverage includes charts for (a) free-space coverage; (b) cov-
erage with lobing (multipath propagation), if applicable; (c)
Figure C50 3D, stacked-beam radar coverage (from Barton,
coverage with ground clutter; (d) coverage with sea clutter;
1988, Fig. 7.3.1, p. 348).
(e) coverage with weather clutter; (f) coverage with combined
clutter (e.g., sea plus weather clutter); (g) coverage with jam- o
60
ming; (h) coverage with combinations of clutter and jam- 15.5 o
ming; and (i) coverage under certain special conditions (e.g.,
13.5 nmi
anomalous propagation, fail-soft operation for solid-state
radar, etc.) To obtain an accurate assessment of radar cover-
age under such conditions, an appropriate description of the
conditions (corresponding to models of clutter and jamming) 50 nmi
must be included (see CLUTTER, JAMMING). 50 nmi
Figure C49 is an example of radar coverage in the eleva-
tion plane for a 2D ground-based, horizon-search radar. The
lobing effects due to interference from surface reflections are Figure C51 Airborne radar ground coverage.
clearly visible in the figure. (See PROPAGATION, wave.)
Other types of radar coverage charts can be prepared to
Figure C50 is an example of the elevation versus range cover-
portray the combined coverage of an air defense network, air
age provided by a 3D, stacked-beam search radar. Complete
traffic control system, or spaced-based ocean surveillance
coverage of the desired search volume would be covered by
system. In general, the broader the scope of the radar cover-
scanning the radar antenna 360° in azimuth.
age information desired, the more difficult and expensive it is
Airborne or spaceborne radars are often employed to pro-
to provide accurate, detailed, and timely information.
vide surveillance or mapping of the surface. Figure C51
Radar coverage charts can be prepared to show target
illustrates the ground coverage, in the elevation plane, of an
detection limits in other-than-spatial dimensions. Figure C53
airborne radar in its air-to-ground mode, and Fig. C52 shows
is a range-doppler map for a multiple-PRF radar, indicating
the wide-area coverage typical of a satellite-based ocean sur-
blind regions within the coverage due to eclipsing effects,
veillance radar.
mainlobe clutter, and range-doppler ambiguities.