Remote Sensing

Section 1. GENERAL PRINCIPLES OF REMOTE SENSING
1.1 USE OF ELECTROMAGNETIC RADIATION FOR REMOTE SENSING
Aerial photography was the earliest form of remote sensing other
than the telescope. For a long time, this technique relied on the
portion of electromagnetic radiation used by our eyes (the visible
spectrum). Early aerial photography was usually obtained on black and
white film which responded to light over a broad range of visible light.
Later, it was learned that by placing a filter in front of the lens
which would pass only a particular color of light, a black and white
record could be made of the objects reflecting light in that range. For
instance, an aerial photograph of a developed area with a red-passing
filter would show bare ground and many man-made surfaces which reflect a
significant amount of red light. Hence, this photograph would be useful
for identifying man-made features. This technique is used by the Landsat
series of satellites today.
Later, as color photography became available, color film was used
in aerial photography. Again, filters could be used to enhance particular
features.
V-I1.1.1 Near Infrared Aerial Photography. During the second World
War there was a need to detect camouflaged objects. Although a great
deal of aerial photography was obtained, it was often difficult to
detect objects which had been painted green or had been covered with cut
tree branches. Some experimental film was developed which responded to
to light in the near infrared portion of the spectrum, light just a
little more red than the red light detected by the human eye. One of
the anticipated uses for this film involved the monitoring of healthy
vegetation whose chlorophyll reflects the near infrared extremely well.
This film was simply a black and white film with extended sensitivity
which would record the near infrared if the visible light was filtered
out. Later, a color film was developed which responded to the near
infrared as...