Image Processing Reference
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context of endmember abundances estimated by the spectral mixture analysis.
This is the approach used here.
Kuwait City and most parts of the Arabian Shield are characterized by a desert
environment with scanty rainfall, and a dry, hot climate. Spring (January-March)
temperatures in Kuwait are generally low and quite pleasant compared to the sum-
mers, especially July with a mean temperature of 37.4°C and a maximum mean
temperature of 45°C. The March average temperature for Kuwait City for the last
50 years is 19.3°C, with a maximum mean temperature of 25.6°C and a mean mini-
mum temperature of 13.2°C. Beyond the limits of Kuwait City, the suburban area
consists of flat undulating desert with more than 50% eolian sand surface deposits.
During the spring rain season the area supports the growth of ephemeral vegetation.
However, desert areas are heavily overgrazed by camels, sheep, and goats, leaving
the soil nearly bare most of the time. Local landscaping, greening, and beautifica-
tion projects were initiated in the 1960s as a source of national pride and to enhance
economic productivity.
New York City, in contrast, is characterized by a temperate climate modulated
by the thermal inertia of the Atlantic Ocean. Annual temperatures generally range
from −20°C to 40°C with seasons dictated by temperature rather than precipitation
cycles. Contrary to popular belief, the New York metro area is characterized by
abundant urban and suburban vegetation in the form of mature deciduous street
trees and numerous parks and public green spaces.
Vegetation fraction images were generated from a three-component mixing
model based on high albedo substrate, vegetation and dark surface that is physically
consistent with the spectral characteristics that might be expected for an urban
environment (Small
2001
). Fractional abundance images resulted from a unit sum
constrained least squares inversion of the linear mixing model using the spectra of
endmembers. The surface brightness temperatures were derived from the Landsat
ETM+ thermal band 6 as explained in
Section 14.4.
Figure
14.1
shows vegetation fraction and surface temperature images for
Kuwait City and New York City derived from Landsat 7 imagery. The Kuwait City
image was acquired under desert springtime conditions on March 6, 2001, while the
New York image was acquired under late summer drought conditions on August 6,
2001. The datasets have been subjected to the same processing and enhancement
techniques and therefore the dark and light tones in the vegetation fraction and
surface temperature images are comparable. The only exception is the Kuwait City
vegetation fraction image in which the brightness to contrast ratio has been increased
by 30% so that features are observable. From Fig.
14.1
, the distribution of vegeta-
tion fractions observed in Kuwait City is generally lower than that in New York
City which has abundant vegetation in the form of large deciduous trees, wetlands
and closed canopy forest in parks and cemeteries. In the New York City image, parks
and public greenspace are easily distinguished. In addition, interurban differences
in street and courtyard vegetation can be consistently detected. Vegetation in Kuwait
City consists of palm and shade trees, shrubs, groundcovers, and grass, which are
irrigated year round (Kwarteng
2002a, b
). In spite of the low vegetation cover
observed in Kuwait City, the relative amounts of the vegetation fractions in different
