f. The electro-optical (E-O) sensor employs digital imaging technology
similar to a thermal sensor to collect imagery in the visual range. Major
advances of E-O sensors are:
(1) Sensor range is much greater than that of film.
(2) The sensor can penetrate light atmospheric
conditions
that
are
opaque to a sensor using photographic emissions.
(3) E-O imagery can be manipulated to reveal the characteristics of an
object that are not readily apparent in the original image.
5. There are four types of film used in aerial photography to assist in
detecting camouflage:
a. Black and white film records images in tone gradation between white
and black. While not reproducing color, it does provide a permanent record
of tonal differences.
Select filters are often used to improve the
photograph or to record only the light that is known to give the greatest
tonal differences between natural backgrounds and the object being sought
(Figures 1-3, 1-6, and 1-9.
b. Color film will detect camouflage which does not match the colors in
the background.
However, this film has many operational difficulties and
gives best results only under ideal conditions.
Colors tend to blend
together at high attitudes, shadow density is not as accurate on this film
as on the black and white film, and atmospheric conditions must be ideal in
order to obtain a clear photograph.
For these reasons, this film is not
widely used.
c. IR waves or rays refer to a position of the electromagnetic spectrum
which is invisible to the human eye. Most things in nature, such as living,
green vegetation, reflect these IR waves readily and in large quantities.
Most artificial materials normally do not reflect these IR waves to the same
extent. Thus, IF film which is nothing more than black and white film that
is sensitive to IR waves, can result in a picture showing contrasts between
natural materials and artificial materials. The natural materials will show
up as a light tone of gray while the artificial materials will up show up as
a dark tone of gray. IR film has another important use. It can be used to
take photographs at night if there is a source of IR radiation. To counter
the detecting ability of this film, camouflage paints and dyes have been
developed that have a high IR reflectance, similar to foliage.
All
camouflage materials are now issued with this type of coloring so that IFR
film can no longer detect differences between natural and artificial
camouflage that has been treated with such paint and dye (Figure 1-11).
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