Monitoring Land Subsidence in the Euganean Geothermal Basin with Differential SAR Interferometry

Land subsidence of the Euganean Geothermal Basin, Italy, is a well-known process which is related to the geothermal groundwater withdrawal. Up to 1991 the maximum rate of land subsidence has been 1 cm/year as observed from precision levelling surveys. From 1991 to 1995 a decrease of land lowering due to a regulation of groundwater withdrawal has been measured. In this study the question of a convenient use of differential SAR interferometry for land subsidence mapping in the Euganean Geothermal Basin was addressed using a time series of ERS-1 and ERS-2 SAR data from 1992 to 1996. Multiple interferograms were combined into a single subsidence map in order to reduce errors caused by atmospheric phase distortions, phase unwrapping, baseline estimation and noise. The analysis revealed a clear subsidence signal over Abano Terme with a maximum annual subsidence velocity of 4 mm/year that is in agreement with the results of the last levelling surveys performed in 1991 and 1995. The comparison of SAR interferometry and levelling surveys also indicates advantages and disadvantages of both techniques, individually used, that should be considered for an accurate, rationale and cost-effective monitoring of subsidence. In any case an integrated survey could provide the best way to investigate the regional subsidence process.