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

I. Homing Patterns (H) are used to locate emergency transmitters
or other radio or electronic emissions from survivors or distressed
craft when the detected signal is too weak for homing equipment to
receive, or the SRU does not have homing equipment. See para 642.C.2.
J. Drift Compensation During a Search. If the target and SRU are
in motion, it may be necessary to consider the relative motion plot of
the SRU with respect to the target, especially in high current areas.
Failure to account for target motion may cause the target to drift out
of the search area before the search is completed. Even if the target
remains in the search area, the pattern relative to the target may be so
distorted that POD is greatly reduced.
1. While it is possible to compensate any search pattern for
drift, in practice compensation is normally applied to
parallel path (PS/CS) searches. To determine whether
compensation is needed, planners ascertain expected velocity
of target drift (v) during the next search, maximum dimensions
(length (l) and width (w)) of the search area, and search
speed (V) and track spacing (S) to be used.
a. If the value of (v x l)/(V x S) is less than 0.1,
compensation for drift is not necessary. Otherwise, orient
the search area so that the major axis is parallel to target
drift direction, and investigate further the problem further.
b. If the value of (v x w)/(V x S) is less than 0.1, no
compensation is necessary. Otherwise, patterns for drift
compensation should be considered.
2. Patterns accounting for search target motion are:
a. Parallelogram Pattern (Pd). In these patterns the
search legs are parallel to target expected motion. The
perimeter of the area relative to the earth can be found by
moving the downcreep side of the uncompensated area the
distance the target is expected to drift during the search of
that area. For multi-SRU searches, the total area should be
divided into adjacent areas which join only along sides
parallel to the search legs (see Figure 5-39). All SRUs
should creep in the same direction with altitude separation
provided for aircraft SRUs. Each area should be compensated
to account for differences expected in drift rate between
subareas.
5-40