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Fig. 6.6 Spectral changes as agricultural land is converted to urban residential land use (Ridd
et al. 1983 )
increased housing density toward the upper (I) vertex near commercial districts, and
grading into low density (typically higher income) residential sites toward the vegeta-
tion vertex.
The spectral transition associated with an agricultural to residential development
is illustrated in Fig. 6.6 (Ridd et al. 1983 ). With the clearing of farmland (Agr), the
spectral signature moves swiftly to the non-vegetation line, suggesting residential
development is about to begin. Roads, driveways, and houses begin to cover bare soil,
darkening the signature. As landscaping commences, and eventually matures, the
signature migrates back toward the green corner, settling somewhere near the center
of the visible/NIR envelope. How near the center depends on, again, the resulting
housing density.
Figure 6.7 illustrates the conversion of arid landscapes to urban use assuming
water is available to establish sufficient landscaping. The residential sequence is
similar but with little or no clearing before development takes place. End results lie
along the V-I and I-S axes as well. Cities rising from arid landscapes with insuffi-
cient water may end up on a more vertical axis from the I vertex downward toward
the center of the ternary diagram.
6.2.3
The Role of Remote Sensing in Urban Systems
As indicated in Fig. 6.8 remote sensing of urban systems provides a basis for inves-
tigations in (1) urban morphology, (2) biophysical systems, and (3) human systems.
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