Image Processing Reference
In-Depth Information
7.2.4
Temporal Resolution
The temporal resolution of a remote sensing system can be defined as either the
theoretical or operational capability for acquiring repetitive imagery over some
time interval. Platform characteristics are the pri-
mary factors influencing the theoretical temporal
resolution. Aircraft are more mobile than space-
craft platforms and provide the potential for tem-
poral resolutions of a few minutes (seconds for
rotary-wing aircraft). Most spaceborne systems
utilize polar-orbiting satellites, with limited repeat
potential from several days to a few weeks. The
spatial extent of images depends on the swath width,
and influences the resulting temporal resolution.
Larger viewing swath widths allow for monitoring of the Earth's surface in shorter
time periods and thus, shorter revisit intervals. Equatorial-orbiting, geo-stationary
satellites have the potential for nearly continuous imaging (i.e., infinitely fine tem-
poral resolution). Operationally, even polar-orbiting satellites tend to achieve higher
temporal resolution than airborne systems, because of their regular orbits and sys-
tematic data collection and archiving capabilities. Also, the pointability of many
newer generation satellite sensors enables higher temporal resolution for polar-
orbiting satellites that would normally have a long repeat interval.
In the early 1970s temporal resolution tended to vary inversely with spatial reso-
lution. The closer the platform is to the earth surface
(i.e., lower the orbit), the higher the spatial resolu-
tion and the lower spatial coverage and therefore,
the temporal resolution. This relationship is valid
for scanning radiometers (such as the Landsat
Thematic Mapper) designed to collect images over
a fixed swath width centered at nadir. However, as
discussed previously, with the advent of pointable
imaging sensors such as SPOT, IKONOS, and Quickbird, that can capture imagery
off-nadir while orbiting the earth, temporal resolutions have been reduced.
temporal resolution
refers to theoretical or
actual revisit time
intervals of the sensor's
platform over the same
location of the earth
surface
a system is called
pointable, if off-nadir
image capturing is
possible, implying an
increase in the revisit
capability of the satellite
Selecting the Appropriate Imagery for Urban Analysis
Given the complexity of urban environments and the high spatial heterogeneity
of urban materials, spatial, radiometric, and spectral resolutions of imagery
should be considered concurrently, with the objective of achieving highest
possible separability of features of interest. Current operational imaging
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