Combined use of space-borne SAR interferometric techniques and ground-based measurements on a 0.3 km2 subsidence phenomenon

The built-up area of the village Hilsprich (Lorraine, France) is affected by a subsidence phenomenon localized over a few hundred square metres, causing damage to buildings. In this study, differential SAR interferometry (DInSAR) was used to:• te the boundaries of the subsidence in order to optimize ground-based monitoring networks (levelling and geophysical measurements) te the maximum deformation and highlight the evolution of the phenomenon (previously unknown due to insufficient historical ground-based data). udy was based both on L-band ALOS/PALSAR SAR data and C-band Envisat/ASAR data. The interest in PALSAR data lies in its better performance for InSAR with respect to C-band data on the affected non-urban areas (such as fields and farmlands) where, in addition, conventional techniques such as topographical survey information were limited, and had often not been carried out before the first damage was observed. Conventional DInSAR based on PALSAR data processing for the 2008–2010 period identified the boundary of the subsidence area and estimated its maximum magnitude. The PSI technique in the ASAR archive gave information regarding the beginning of the subsidence. The precision of the DInSAR results was consistent with the topographical data (in locations where this information was known) and therefore favours the SAR interferometric techniques in this context. Combined with the knowledge of the regional geological and structural setting, together with results from ground-based electrosounding, the results of the study established a basis for an increased understanding of the subsidence phenomenon, which was revealed to affect an elliptical bowl-shaped area due to salt dissolution.