Ground deformation in the Greater Zurich Area from differential SAR interferometry

Space borne Differential Synthetic Aperture Radar Interferometry (DInSAR) is a consolidated remote sensing method used for the analysis of surface deformation at regional scales. Nowadays, archived multi-temporal satellite acquisitions allows generating time series of ground deformation spanning periods as long as 20 years. Moreover, the advent of new satellite missions, such as the ESA Sentinel-1, will increase our capability to identify and monitor surface displacements over space and time. Advanced DInSAR methods have been developed in the last decade to derive ground velocity maps and displacement time series. Among several, the Small Baseline Subset (SBAS) technique combines sets of interferograms with small orbital separation (baseline) and short revisiting time to reduce the temporal decorrelation and maximize the number of coherent SAR targets. SBAS has proven to be suitable in different scenarios, with accuracies of 1 mm/year for mean surface velocities and 5 mm for displacement measurements. In this work, we present surface velocity maps and displacement time series obtained in the Greater Zurich Area (GZA) by processing the ASAR Envisat data acquired from two different satellite orbits (ascending and descending) in the 2002-2010 time period. The SAR data was processed by leveraging a new service released within the ESA GRID-based operational environment, i.e. the unsupervised parallel implementation of the SBAS algorithm. The main advantage of this approach is that users with different backgrounds, more interested in the analysis of the surface deformation than in the details of the SAR data processing, can apply a reliable and validated state of the art algorithm without downloading large amounts of input data, nor owning costly processing hardware, or learning specific software. Despite a general overall stability, our results show interesting deformation patterns in the GZA. Here we illustrate the technique and show examples relevant to a known landslide in the Limmat valley, subsidence located in the vicinity of the Zurich and Zug lakes, as well as deformation patterns likely related to anthropic activities.