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183 | 210 | 188
148 243 | 274 | 211
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214 | 248 |>279| 276 | 211
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b Band 7
Figure 8. a Anomaly on Landsat TM7 image (16 March 1985) within a crater of the
Luscar volcano, Chile; b corresponding TM7-based pixel-integrated temperatures. (a,b
Francis and Rothery 1987)
distribution of temperature and movement of coal fires. Such
information would hardly be available by any other technique.
4. ESTIMATION OF GROUND DEFORMATION
RELATED TO EARTHQUAKES, VOLCANISM, CREEPS
4.1 Physical Principle
There has always been a need for estimating surface
deformation and movement related to earthquakes, volcanism,
tectonic movements, creeps, landslides, glaciers etc. This type
of data can make valuable inputs in natural disaster
management, as well as in modelling Earth's processes.
The conventional method of aerial photo interpretation have
long been used to map faults and lineaments, and deduce
directions of relative movements in the geological past,
wherever possible; but these methods fall short of the needs,
particularly in natural hazards and disaster management.
Synthetic Aperture Radar (SAR) interferometry (InSAR) has
emerged as a powerful technique for producing digital elevation
models (DEMs). The method combines complex images
recorded by SAR antennas at different time-instances to
generate interferograms. This permits determination of
differences in the 3-D location of objects, i.e. generation of
DEMs. The DEMs have wide application for geoscientific
studies, e.g. for topographic mapping, geomorphological
studies, detecting surface movements, earthquake and volcanic
hazard studies, landslide studies and several other applications.
The basic strength of SAR interferometric technique is that the
difference in distances from any two antenna positions can be
measured with fractional wavelength accuracy in terms of phase
difference. The phase difference can then be processed to derive
height information, i.e. generate a DEM.
Differential SAR interferometry can detect relative changes, of
the order of a few centimeters or even less (Gabriel et al. 1989).
The technique utilizes three or more SAR images, which are
processed to yield two or more interferograms (Fig. 9). Then
from a set of interferograms, a difference image is generated to
depict surface changes and movements that have taken place in
the intervening period.
4.2 Methodology
Figure 9. Principle of differential SAR interferometry
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