Image Processing Reference
Figure1.11 False color key to LANDSAT image of San Francisco Peninsula (red: high
reflectance at blue wavelengths; green: high reflectance at near-infrared wavelengths; blue:
high reflectance in visible wavelengths). Built-up areas appear purple or gray, white areas
are high albedo objects, vegetation appears green because of its high near-IR reflectance,
and clear water appears black.
of light using different colors. The Marin Headlands in the upper left corner are
heavily vegetated, as are the East Bay hills to the right and the mountains in the
lower right corner. Urban areas show up as light gray, indicating that they have
a lower near-infrared reflectance. Buildings, streets, and parking lots absorb much
more near-infrared light, raising the summer temperature in some cities by as much
as 5 to 10 degrees centigrade over that of nearby heavily vegetated areas (the so-
called “heat island” effect).
Infrared light often is reflected off surfaces differently from visible light, which
is the principle behind the detection of the camouflaged factory in Fig. 1.10.
Infrared light is also absorbed and transmitted differently than visible light, and
this property can be used to see through layers of material that absorb visible light
but transmit infrared.
The absorption or transmission of infrared light in a particular molecular
material (e.g. wood, paper, ink, leaves, glass) is determined by the presence or