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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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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).