Answer:
Color infrared photography, often called false color
photography because it renders the scene in other than
the normal colors seen by the human eye, is widely
used for interpretation of natural resources.
Atmospheric haze does not interfere with the
acquisition of the image, therefore is well suited to
aerial photography. Because the film is high speed and
subject to degrees of degradation in handling before
exposure, the aerial photographs can vary in overall
tone. This variability complicates the interpretation
of color tones between photographs. However, some
general guidelines can be given to aid the
inexperienced interpreter.
The red tone of color infrared aerial photographs is
almost always associated with live vegetation. Very
intense reds indicate vegetation which is growing
vigorously and is quite dense. An irrigated alfalfa
field would be an example of such vegetation. An
evergreen forest, which may be quite dense
vegetatively, will not appear as a similar bright red
because its level of growth activity is less, compared
to irrigated alfalfa. Knowledge of the vigor and
density of vegetation is important to the
interpretation of the red colors on color infrared
aerial photography.
As
the vigor and density of vegetation decreases, the
tones may change to light reds and pinks. If plant
density becomes low enough the faint reds may be
overcome by the tones of the soils on which the plants
are growing. The ground areas in this case will appear
in shades of white, blue, or green depending on the
kind of soil and its moisture content. As plant vigor
decreases, the vegetation will show as lighter shades
of red and pink, various shades of greens, and
possible tans. Dead vegetation, wheat stubble as an
example, will often be shades of greens or tans.
Bare soils will appear as shades of white, blue, or
green in most agricultural regions. In general, the
more moist the soil the darker the shade of that
particular soil color. Composition of the soil will
affect the color tones shown on the photographs. Dry
sand will appear white and, with more moisture, may be
very light gray or possibly light tan. Clayey soils
will generally be darker in color than sands and tend
toward tans and bluegreens. Again, wetter clays will
be darker shades of the same tones. Soils high in
organic matter, like silts and loams will be even
darker in color, and usually in shades of blues and
greens. Wet organic soils can be very dark blue or
green in the aerial photographs.
Man-made features will show in the tones that relate
to the materials they are made of. Asphalt roads, for
example, will be dark blue or black, gravel or dirt
roads will show as lighter colors, depending on the
soil materials involved in their composition, and concrete roads will appear light in tone,
assuming clean concrete. The buildings and streets of
towns can be considered in a similar manner, their
color dependent on the material they are made of.
Water will appear as shades of blue, varying from
nearly black to very pale blue. Clear, clean water
will appear nearly black. As the amount of sediment
increases, the color becomes increasingly lighter
blue. Very shallow water will often appear as the
material present in the bottom of the stream. For
example, a very shallow stream with a sandy bottom
will appear white due to the high level of reflection
of the sand.
Degraded film will result in photographs which have an
overall blue or green cast. When that occurs, the
interpretation must consider what that overall cast
will do to a "normal" rendition of the scene.
