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

2. This section provides sweep widths for a limited range of
target types and sea conditions. For other targets and sea
conditions, the manufacturer's detection performance estimates
should be used when available. Manufacturers should have
completed extensive testing of their products and may be able
to provide detection capabilities for particular targets and
specified environmental conditions. If this information is
not available, the SMC may ask radar operators for estimates
of sweep width based on operational experience. An
experienced radar operator familiar with the assigned radar
should be able to offer fairly accurate estimates of effective
(not maximum) detection range. Radar operators should be told
that the effective detection range is the range at which they
believe the target will certainly be detected under prevailing
conditions. Sweep width can be calculated as about twice this
estimate of effective range. Sweep width estimates for small
fiberglass or wooden craft that may be capsized are based on
the assumption that the target has no engine or significant
metal equipment exposed.
3. The Douglas scale (see Table 5-9) is a series of numbers from
0 to 9 to indicate sea condition, and was used in the
development of the radar sweep width tables. Douglas sea
states over 3 are not used because little data has been
collected under these conditions, and most radars show
excessive sea return (clutter) above sea state 3.
TABLE 5-9. Douglas Sea State
Douglas Sea State Description Wave Height
O Calm --------
1 Smooth 0 - 1 foot
2 Slight 1 - 3 feet
3 Moderate 3 - 5 feet
4 Rough 5 - 8 feet
5 Very Rough 8 - 12 feet
6 High 12 - 20 feet
7 Very High 20 - 40 feet
8 Precipitous over 40 feet
9 Confused --------
4. For Surface Vessel Radar (SVR), the following sweep widths can
be used, based upon data from AN/SPS-64(V) and AN/SPS-66
radars:
5-22