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Figure 3: Result of the screening analysis over an area of 28 by 12 km based on 10 ERS interferograms. The deformation velocity
field, which was estimated between June 1995 and August 2000, is superposed to a SAR amplitude image of the same area.
3. DISCUSSION OF RESULTS
The above described DInSAR procedure can be employed in
different operational contexts. In this paper we describe two
applications. The first one is a screening analysis, which
allows unknown subsidence phenomena over large areas to
be detected using a limited set of SAR images. In this
application the major emphasis is on the “early detection” of
unknown deformations, rather than on a quantitative
estimation of the deformations. For this reason, the analysis
can be performed using a limited SAR dataset. This low-cost
deformation detection takes full advantage of the wide arca
coverage of the SAR images, which typically cover 100 by
100 km. The second type of application is a quantitative
analysis of an already known deformation area: a urban
subsidence of small spatial extent due to mining activity.
The above described screening procedure was used over a
test area of about 340 km“, which is located in Catalonia
(Spain), where no a priori information on land deformation
was available. The analysis was based on 10 interferograms,
Which were computed from 13 ERS ascending SAR images.
These images cover more than five years, from June 1995 to
August 2000. The interferograms have different values of
temporal baseline (the time interval between the acquisitions
of M and S), which span from 630 days up to 1750 days. The
fest areas is shown in Figure 3, where the deformation
velocity field is superposed to a SAR amplitude image. As it
could be expected, most of the considered region shows no
deformation. However, there is a relatively big area of about
4 km” with is characterized by a deformation rate of about 5
mm/yr, and other deformation areas of small spatial extent,
Which show deformation rates up to 10 mm/yr. It is worth
noting that this only represents a first detection of these
subsidences, whose actual importance will be assessed in the
future. However, this example shows the potential of
DINSAR as an “carly detection tool” of deformations.
167
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0 10mm/year
Figure 4: Result of the screening analysis over an industrial
area, whose location is shown by a white frame in Figure 3.
The deformation velocity field is superposed to a 1:5000
orthoimage of the Cartographic Institute of Catalonia (ICC).