Land subsidence detection using long interval ERS/SAR data pairs

Actual possibility to extract interferometric fringes from long time interval ERS-1,2/SAR data pairs were evaluated. One of the test sites is eastern part of Saitama prefecture, which lies to the north of Tokyo, capital of Japan. Land subsidence caused by pumping water is reported in this area. Interferometric fringe pattern is not extracted from the data pairs with long baseline distances (more than 790 m), therefore, short baseline distance data pairs (less than 91 m) are used for the attempt. Coherences computed as the complex correlation coefficients between two SAR complex data reduce with time interval and indicate obvious temporal decorrelation. Interferometric fringes are obtained from the data pairs which interval are less than 1261 days even though their coherence are low. The data pairs which interval are 1739, 1774 and 2194 days do not indicate fringe pattern in spite of their baseline distance are short enough. Detected phase difference patterns agree with the leveling results. The result of this study suggests the possibility to detect a long-term land subsidence using around 3.5 years interval ERS-1,2 SAR data pairs.