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

Figure 5-19. Maritime Probability of Detection
C. For an area that has been searched repeatedly, with appropriate
corrections made for drift, a Mean Coverage Factor (Cm) is obtained by
averaging the individual search coverage factors. Cm is then used with
the appropriate search curve of Figure 5-19 to determine the Cumulative
POD. For a sixth or subsequent search, the fifth search curve should be
used. Cumulative POD should be calculated by the SMC at the conclusion
of each search. A high Cumulative POD for successive searches of an
area without locating the target may indicate the target was not in or
has drifted out of the search area, has sunk, or has changed
characteristics and requires a reevaluation of search area and coverage
(e.g., primary target changes from a fishing vessel to a liferaft).
D. For searches involving multiple resources, an overall coverage
factor is calculated as outlined in paragraph 541.D. This coverage
factor is used with the first search curve of Figure 5-19 to determine
POD for the total area searched. If the search is unsuccessful, the
search area should be expanded, using the search radius safety factors
in paragraph 522, and a new overall coverage factor calculated. The POD
for that particular search is determined as before, and the Cumulative
POD is found by averaging the overall coverage factors and using this
average coverage factor with the first search curve of Figure 5-19. The
second through fifth search curves are not used because, with each
successive expansion, a portion of the total search area is being
searched for the first time.