Water (Water, Clouds, Snow, and Ice)

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limestones, and blue-gray = unaltered volcanics.

Courtesy of NASA/GSFC/METI/ERSDAC/JAROS,

and U.S./Japan ASTER Science Team.

(d) Water (Water, Clouds, Snow, and Ice). As previously mentioned, the

near infrared defines the landwater boundaries. The transmittance of radiation by

clear water peaks in the blue region of the spectrum. A ratio of band 5/band 2 is

useful in delineating water from land pixels. Mid-infrared wavelengths in the 1.5-

to 1.75-mm range distinguishes clouds, ice, and snow. See Figure 5-32.

(e) Urban Settings. Objects in an urban setting include man-made fea-

tures, such as buildings, roads, and parks. The variations in the materials and size

of the structure will greatly affect the spectral data in an urban scene. These fea-

tures are well depicted in the visible range of the spectrum. Near infrared is also

useful in distinguishing urban park areas. Urban development is well defined in

false-color and true color aerial photographs, and in high resolution hyperspectral

data. The thermal infrared range (10.5 to 11.5 m) is another useful range owing

to the high emittance of energy. A principal components analysis may aid in

highlighting particular urban features. See Figure 5-33.

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