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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004 
  
3. METHODOLOGY 
3.1 Selection of Data Pairs Appropriate for SAR 
Interferometry 
Base length values need to be calculated for selection of 
appropriate data pairs. A base line expressed by the length B 
and an inclination angle of a between two SAR antennas may 
also be expressed in horizontal (By), vertical (B,), perpendicular 
(B,) and parallel (Bj) components, as shown in Fig. 1. There 
exist a number of methods to compute base lengths. 
tat paths 
  
Figure 1. Interferometric Base Length Expressions 
Base length values were computed using DESCW program for 
selection of data pairs suitable for interferometry. Data having 
base length less than 600m are suitable for SAR interferometry 
(Gens, R., 1998). Therefore the data of 22556 and 23057 orbit 
numbers and the data of 42229 and 42730 orbit numbers are 
suitable for SAR interferometry process. However in this study 
we only used the data having 22556 and 23057 orbit numbers. 
3.2 Data Analysis 
After selection of appropriate data pairs ROIPAC software was 
used to analyze the data of 22556 and 23057 orbit numbers and 
the phase difference image depicted in Figure-2 was obtained. 
Since each fringe in this image corresponds to a 
deformation of 28 mm, which is half the wavelength, a 
total of 27 fringes are counted from the Black Sea Coast 
to the north of the Izmit Bay and the total deformation is 
calculated as ~75 cm. 
A number of techniques are then used to obtain the deformation 
information (deformation in the view direction of the satellite) 
using this image. 
  
  
  
  
  
Figure-2. Interferogram obtained from the data acquired on 
13.08.1999 and 17.09.1999 using the ROIPAC software 
Phase Unwrapping is one of the techniques employed. An 
interferogram image directly contains the phase information 
dependent upon the terrain topography. Since this phase 
information is given modulus 27, the integer coefficients of 2x 
needs to be calculated to determine the ambiguity, which is 
called, phase unwrapping. Although a variety of methods have 
been invented for phase unwrapping, which is the most 
important step in the interferometry technique, none of these 
gives exact results.[Rüdiger] 
For the interferogram image in Figure-2, each fringe was 
manually digitized as given in Figure 3, instead of using the 
phase unwrapping technique. Fringes were not clearly obtained 
on the fault line and its vicinity. There are two reasons for this. 
First, the deformation rate is probably too high. Second, 
temporal decorrelation in the rapture zone area is extreme 
because of the loss of coherence in the damaged areas. 
Therefore it is essential to make additional observations near 
the fault to estimate the ground deformation. 
  
  
  
  
  
Figure-3. Fringes manually digitized 
3.3 Estimating Absolute LOS Deformation from GPS 
measurements 
The slant deformation amount can be computed only in the line 
of sight of the satellite using radar data. d,,d,,d, 
respectively denote deformation components in north, east and 
vertical directions, dr denotes deformation component in the