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

problem, colors are more easily distinguished, and
target/background contrast is better.
b. Target detectability, however, has been shown to be
essentially the same whether an SRU passes a target on the
up-sun or down-sun side. These relationships are illustrated in
Figure 6-10.
6. Aircraft movement causes the field of view to be moved along.
Eye movement should be away from the aircraft to the maximum
detection range and then back toward the aircraft to a point
as near under the aircraft as can be comfortably seen.
Aircraft should consider using scanners from rear observation
positions. For surface SRUs, the direction of movement is not
as important. A systematic pattern that does not leave voids
in the field of vision is all that is needed.
7. Night scanning poses additional considerations.
a. Eyes require about 30 minutes of dark adaptation,
best accomplished in total darkness. However, the wearing of
red goggles enables dark adaptation to occur in a lighted
room. Exposure to intense sunlight may cause a person's dark
adaptation threshold to rise, and the effect may take several
hours to wear off. When a night search is scheduled, the crew
should wear dark glasses during brilliant sunshine. The trip
to the search area should be used for dark adaptation by
ensuring that the SRU interior is dimly lit, with red light if
available. Dark adaptation can be hindered by lack of oxygen,
and by consumption of cigarettes and alcohol.
b. Night scanning can use any systematic geometrical
pattern. Maximum effectiveness in night scanning is achieved
by a series of short, regularly spaced eye movements.
Scanners should concentrate their search on the horizon where
the contrast between the craft's silhouette and the sky would
be greater than the contrast between the dark target and the
dark ocean surface. On the other hand, if the distressed
craft is able to illuminate itself, the contrast would be
greater against the dark ocean than against the lighter sky
and low stars. If the search is being made at night with
expectations of finding light signals or flares, the eyes need
not pause so frequently in sweeping the visual field.
Periodically, the lookouts should close their eyes for a
period of 5 seconds to allow rest.
c. When binoculars are used for scanning at night, the
principle of off-center vision still applies. Binoculars
should be held straight forward and the eyes turned off-center
toward the perimeter of the field. The scanner should avoid
looking directly at any object located by scan, and should
look instead off-center, thereby preserving night vision. A
single stationary point of light may appear to move aimlessly.