Image Processing Reference
In-Depth Information
other land use categories however, application of remotely
sensed observations to studies of the urban environment
has been very limited. In part, this is because accurate
identification of most built components of the urban envi-
ronment requires finer spatial resolution (see Chapters 5
and 6) than has traditionally been available from opera-
tional satellites such as the Landsat or Satellite Pour
d'Observation de la Terre (SPOT) sensors. The 30 m spa-
tial resolution of the Landsat Thematic Mapper (TM) sen-
sor is comparable to the characteristic scale of urban land
cover (Welch 1982 ), but is generally too coarse for identi-
fication of individual structures. While this resolution has
limited Landsat and similar satellites' use for studies of
the built urban environment, it is sufficient to detect signifi-
cant spatial and temporal variations in urban land cover and surface conditions -
specifically vegetation, albedo, and surface temperature.
The most successful applications of remote sensing to the urban environment
generally involve measurement of physical quantities related to environmental condi-
tions such as vegetation abundance and surface temperature. In spite of the great
value that remotely sensed measurements can provide to the study of urban environ-
ments, it is important to acknowledge the limitations of these tools. While remotely
sensed imagery provides an invaluable reconnaissance and monitoring tool, there are
often other sources of environmental information that are more accurate and informa-
tive (Miller and Small 2003 ). This chapter explains the rationale and techniques for
urban vegetation and surface temperature mapping from satellite imagery, and illus-
trates the differences in two cities, New York and Kuwait City, by comparing their
surface properties and their influence on energy flux using Landsat 7 imagery.
the synoptic view
of urban land
cover provided by
satellite-based
sensors
complements
in situ
measurements
of physical and
environmental
conditions in
urban settings
14.2
Urban Physical Environment
The physical environment of a large city is profoundly different from the physical
environment of small settlements in rural settings. The spatial agglomeration of
built surface in most cities has different physical characteristics from most naturally
occurring environments. These physical characteristics influence environmental
conditions by changing the flux of mass and energy
through the environment. Most of the inhabited areas on
Earth are characterized by soil and vegetation but built
environments are dominated by more impervious surface
and have relatively small amounts of vegetation. Soil
retains moisture and allows for continuous evaporation to
the atmosphere while impervious surface increase runoff
and significantly reduce evaporative moisture flux in the
urban environment.
built environments
are dominated by
more impervious
surface and have
relatively small
amounts of
vegetation
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