the relief and deformation will not be accurate. These areas mask at the step of phase sweep, and common interpolation is performed in them.
Relief and deformations are evaluated only in areas with higher coherence. In this case, the image coherence of the interferometric couple is rather high, about 0.6-0.8 for most pixels of the coherence map.
Then, interferogram filtration with the adaptive algorithm was performed. Filtration was set at a minimum, as in this case the interferogram was almost ideal. Filtration results are presented in Fig. 7.
The filtered interferogram has undergone phase sweep. Direct sweep was done only in areas with sufficiently high coherence (the threshold value is selected interactively and is an expert judgment). In areas of low coherence, values were interpolated. Then, the swept phase was transformed into the geocoded absolute digital relief model shown in Fig. 8.
The length accuracy of the output DRM generated by analyzing the interferometric couple phase component is estimated in the first several meters. Still, these data could theoretically be used to trace subsidence in the Urengoi and Yamburg fields with centimeter or even millimeter accuracy.
An example of the generation of the earth surface deformation field based on the above photo couple is shown in Fig. 9. A pronounced slanting interference is visible, resulting from the inaccuracy of determining orbital parameters of the ERS-1 satellite after an accident on June, 5.
This example proves once again the importance of the exact determination of orbital parameters in interferometric processing.
Modern radar satellite systems (Radarsat-1 and especially ENVISAT) ensure accuracy sufficient to map centimeter and millimeter subsidence without the complicating effect seen in Fig. 9.
Thus, the intensity and amplitude of displacements in the Urengoi field can be determined reliably only after a survey using the aforementioned modern satellite systems with the positioning of radio signal corner reflectors