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Description of  RADAR INTERFEROMETRY

Soon after the first attempts at Delft University of Technology to apply the radar interferometric technique for the monitoring of subsidence due to gas extraction in the province of Groningen, the Netherlands, it was recognized by Usai and Hanssen (1997) that man-made features remained coherent in radar interferograms over long time spans, while their surrounding was completely decorrelated. This particular area in the northern part of the Netherlands is well-known for its subsidence. Due to the slow subsidence rate—the maximum is approximately 1 cm/y—long temporal baselines needed to be used. Even though only interferograms with short perpendicular baselines were generated, temporal decorrelation severely limited the analysis, see (Usai, 1997, 2000; Usai and Klees, 1999). The Groningen data set was also used by Hanssen (1998), who analyzed artifacts of atmospheric origin in coherent interferograms with short temporal baselines. Aside from temporal and geometrical decorrelation, atmospheric signal is the main problem for the interpretation of interferometric signal of current day spaceborne sensors on board, e.g., ERS, ENVISAT and RADARSAT (Hanssen, 2001).