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

B. Forward-Looking Infrared (FLIR) search is a passive detection
system used to detect thermal radiation.
1. All objects emit thermal radiation. Because the quantity of
radiation is temperature dependent, a FLIR system observes the
temperature differences to produce a video presentation. FLIR
can detect objects in total darkness and in the presence of
limited obscurations, such as dust, smoke, and haze.
2. FLIR detection capability is influenced by sea state and
atmospheric content. Sea state is the primary limitation on
maritime FLIR detection in clear weather. Rough seas mix
surface and subsurface water, resulting in cluttered FLIR
image. This makes small targets such as life rafts difficult
to detect, and persons in the water nearly impossible to
detect. The effects of sea state on detectability of medium
and large targets is not as great. Water vapor, carbon
dioxide, and aerosols in the atmosphere will reduce the
effectiveness of FLIR; in some cases, these factors can
degrade FLIR detection performance more severely than visual
detection performance.
3. Visual searchers normally achieve better detection performance
than FLIR in clear daylight conditions. Consequently, FLIR is
a preferred night search sensor, unless certain daylight haze
or smog/smoke conditions impair visual detection more than
FLIR detection.
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