Figure 1-17.
Shadow.
5. Shade.
The distinguishable variations of gray in which an object
appears on a black and white image are known as its tone or shade (Figure 1-
18). The shade of an object is almost entirely due to the amount of light
reflected from it to the camera.
Light reflection, in turn, depends on a
number of contributing factors, such as the texture of the surface, position
of the sun, and wind velocity.
a. The wind may disturb the reflecting surface of a body of water, or it
may expose an entirely new surface to reflected light, as when the wind
bends crops or vegetation. Therefore, the shade of an object may vary even
on two consecutive images of the same mission.
b. Thus, when the earth, grass, or vegetation is crushed flat, say by a
tank or truck, the reflected light will be altered from the norm. Depending
on weather conditions, tracks made by one man walking across a grassy field
can be detected up to 48 hours later on images taken from 30,000 feet.
Figure 1-18.
Shade.
6. Surroundings (Figure 1-19).
This factor is applied as an
aid
to
identification in instances where an object under consideration is:
a. One of a number of similarly shaped objects; for example, shellholes
or fighting positions.
b. Too small to be identified by size, shape, or shadow.
19
IT 0649
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