Image Processing Reference
In-Depth Information
Table 6.1
Comparative energy and moisture exchange rates
Healthy green
vegetation
Impervious
surface
Exposed soil
Water
Energy
Insolation
Drives
photosynthesis
and evapo-
transpiration
Reflects some,
but absorbs
most
a
;
becomes a
heat radiator
Generally
absorbs and
becomes a
heat radiator
Absorbs and
stores energy;
radiates very
little
Diurnal heat flux
Minimal
Great
Moderate
Miniscule
Moisture
Precipitation
Intercepts and
stores in plants
and soil;
retards runoff
Promotes
rapid runoff
miniscule
storage
Intercepts and
stores;
intermediate
runoff rate
Accepts
and stores
Evapo-
transpiration
Significant
transpiration
and evaporation
Miniscule
evaporation; no
transpiration
Moderate
evaporation;
no transpiration
Considerable
evaporation; no
transpiration
a
Depending on brightness
Table 6.2
Sample sites of various urban/peri-urban environments
Percent
Sample site
V
I
S
Description of environment
1
8
87
5
Commercial area
2
36
60
4
High density residential
3
65
30
5
Low density residential
4
90
5
5
City park
5
5
65
30
Sparsely vegetated industrial
6
70
5
25
Forest or farm field in crop
7
23
1
76
Desert shrub land
8
10
20
70
Primitive village in arid land
of homogeneous pixels, an area such as a city block, a
spatial unit such as a CBD, residential area, golf course,
city park, or industrial complex, for example, or an entire
settlement. Sampling strategy may be based on random
pixels, a grid of pixels, all the pixels in the area, or a linear
transect of pixels through an area of interest (AOI).
Table
6.2
shows several hypothetical sites consisting of
various combinations of cover composition. Figure
6.2
places each of the sites in the V-I-S model. In each case the
combination sums to 100%.
Note that for most built-up urban landscapes (espe-
cially in the developed world) there is typically very little
exposed soil, usually not more than 5% (aside from some industrial sites or land
undergoing conversion). Consequently, the V-I-S difference between sections of
the city typically results in a tradeoff between vegetation and impervious surface.
Industrial areas may be an exception, especially in arid lands, where exposed soil
the V-I-S model
provides a scalable
means of revealing
the anatomy of a
targeted object,
whether this object
represents a pixel,
a neighborhood,
or an entire urban
region
