1. The analysis of IR imagery requires that you become familiar with some of the same basic
characteristics used in the analysis of conventional photography. This includes size, shape,
shade (tone) shadow, and surroundings (pattern and site).
NOTE: On negative IR imagery, hot targets will appear black, and cold targets will appear
white. When a print (positive) is made from the film negative, the reverse is true.
Specific aspects of IR imagery discussed in this subcourse are based upon film
negative imagery unless specifically stated otherwise.
2. Five "Ss" are size, shape, shadow, surroundings, and shade and are applied in a slightly
different manner than in regular photography.
Size and shape. You can use size and shape characteristics if you keep in mind the
resolution limitations of the IR system. IR imagery may not often portray the true size and
shape of objects. This is because of three major effects:
(1) Halation or blossoming. A "halo" effect appears on imagery when an object is
considerably hotter than its surroundings. This creates an aura which enlarges the object on
(2) Incorporation is achieved when a large object touches or covers a smaller
object. This results in one large target on the imagery giving misinformation regarding target
size, shape, and numbers.
(3) Overloading. The IR recording system can be overloaded when sensing an
object is too hot for its established range. When this happens the imagery will reflect a large,
unidentifiable mess. The apparent shape may not indicate the object's true shape.
Size and shape characteristics can be used in detecting decoys. Annotation A in
Figure 1-9 shows decoy helicopters and Annotation B depicts actual helicopters.
Shadows. A unique feature of IR imagery is shadows. Shadows will appear on
daylight imagery and be missing on nighttime missions. Shadows are referred to as either
"thermal" or "ghosting."
(1) Thermal shadows can include the same areas as visible shadows. They are
caused by the ground surface temperature being lower in the area shaded from direct
radiation and from a reduced amount of near-IR solar radiation reflected from the shaded
area. True thermal shadows are present during daylight hours. This is caused by shading
from buildings, trees, or other elevated objects. These shadows usually dissipate shortly after
sunset or when cloud cover is present. Dissipation rates vary depending on the physical
characteristics of the