Long-term GNSS and SAR data comparison for the deformation monitoring of the Assisi landslide

A relevant part of the Assisi urban area (central Italy), built up after 1950 and located outside of the ancient town center, is interested by a landslide characterized by a slow rate of movement, which has caused important damages to buildings for an accumulation effect in time. The movements of the soil surface have both a horizontal and a vertical component. A GNSS network for deformation monitoring purposes has been established over the area since 1995, connecting by means of a baseline network the moving region with stable geologic formations located well outside of the landslide body. Further (1999), a leveling network has been added to improve the definition of the vertical component of the motion field. Surveys of both GNSS and leveling networks have been carried out in time, with an approximately annual cadence, until the actuality. Time series of coordinates and heights spanning along the observation period (1995-2010) are hence available for the network points. The Assisi landslide area has also been investigated by means of satellite SAR interferometry InSAR: the data here presented derive from the analysis of ENVISAT ASAR data spanning in time from 2003 to 2010, thus with a 7-years overlapping with the GNSS and leveling surveys, which make possible a comparison. The comparison has been made for each GNSS marker with the surrounding InSAR scatters, trying to take into account local topological effects when possible. A good agreement between the results of the different techniques has been found in most cases, and a deeper analysis of the movement field and the landslide edge is derived from the complete set of data.