JP 3-50 National Search and Rescue Manual Vol I - US Navy

Figure 6-16. Factors in Radar Detection
4. Radar detection is affected by a variety of environmental,
target, and controllable parameters. Wind and sea state
affect the amount of sea clutter present on the radar display.
Rain, water vapor, snow, and other atmospheric content can
have a drastic effect on radar detection ranges. Target size,
shape, and material all affect radar detection range. In
general, metallic targets are most detectable, while wood,
fiberglass, and other "soft" targets are much less detectable.
Target size determines the amount of transmitted power that
potentially can be reflected and the size of the target's echo
on the radar display. The effects of target shape on
detectability are complex, but when devices such as radar
reflectors are designed specifically to maximize the returned
target echo, they can increase detection range dramatically.
Antenna height affects the radar horizon and the grazing angle
of the radar signal with the ocean surface. In general,
shallow grazing angles produce the least clutter. Low
altitudes are best when searching for most common SAR targets.
Figure 6-16 illustrates the relationship between antenna
height, horizon range, and grazing angle. Radar searches
should always be used when:
a. A target may be detected by a radar-equipped search
platform available in addition to primary SRUs using visual or
other search methods.
b. Radar sweep width for the target and prevailing
conditions is greater than for visual or other available
search methods.