Image Processing Reference
In-Depth Information
As you might expect, UV light is not transmitted through the atmosphere in the
same way as visible light or NIW/SWIR light. Aerosols and particulates in the air
tend to absorb and scatter UV. Certain types of air pollution absorb UV light and
get converted to other chemicals. Every good film photographer has a 2A haze filter
for their camera lenses. These filters protect the lens surface and also reduce UV
haze that is especially apparent in landscape photography.
Figure 1.41 shows four images of the moon and the landscape around Nellis Air
Force Base in Las Vegas. The UV image is highly affected by haze in the air that
makes the mountains less distinct and by Rayleigh scattering of UV light by the
atmosphere that completely obscures the moon. The visible image of the moon is
hard to see against the bright blue sky. In the near-IR band, the moon is much more
distinct, as the sky brightness diminishes and the effects of haze in the air become
less substantial.
This chapter has included many examples of differences between near-IR, near-
UV, and visible light in terms of their reflection by and transmission through
materials, yet there can also be significant differences between the amounts of
visible and infrared emissions by a luminous object such as a flame. The presence
Figure1.41 The setting moon over Nellis Air Force Base in near-UV, VIS, near-IR, and
midwave IR wavebands. (Midwave IR image courtesy of FLIR)
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