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

B. POD can be increased by decreasing track spacing, but decreased
track spacing means that more time is needed to search an area with the
same number of SRUs. If extra time is not available, the search area
may need to be reduced. Conversely, search area can be expanded by
increasing track spacing, but this will decrease POD. Unless an optimum
number of SRUs is available, the SMC must choose between the amount of
area to be covered and the POD desired. See Figure 5-15.
C. The practical limits of SRU turning radii and navigational
accuracy limit how much track spacing can be reduced. Optimum track
spacing yields maximum POD during the time available, consistent with
the economical use of available SRUs.
535 Sweep Width
A. Sweep width (W) is the distance on both sides of the SRU where
the probability of detecting a target outside of the sweep width is
equal to the probability of missing a target inside that distance. It
is a measure of detection capability based on target characteristics,
weather, and other factors. Sweep width is less than twice the maximum
detection range, which is the farthest range at which the target can be
detected. See Figure 5-16. It is usually expressed in yards for
underwater and ground searches, and in nautical miles for other types of
searches. Use of the sweep width concept in any search allows solution
of otherwise unworkable problems.
B. Sweep width varies with the type of search conducted. Visual
searching is used most often. However, sensor searches can be far more
efficient than visual and should be considered when it is known, or even
suspected, that the distressed craft or persons may be more readily
detected by electronic or other nonvisual means.
1. Sensors include radio, radar, magnetic, voltage, radioactive,
infrared, ultraviolet, electro-optical, and other
electromagnetic signal sensing equipment. Most common in SAR
applications are radio and radar, with infrared becoming
increasingly available. Detection range information may be
available from parent agencies, operating commands,
manufacturers, or operators. Chapter 6 has additional
information on use of electronic equipment for searches.
2. Each SAR agency should test its specific equipment to develop
accurate estimates of sensor sweep width. Output power,
reflective capabilities, antennae heights, environmental
ambient noise and clutter levels, and other factors that
affect the quality of sensor receiving and transmitting may
affect sweep width.
5-18