Monitoring landslide displacement fields at different temporal scale by using GB-INSAR

The application of SAR Interferometry technique (InSAR) for landslide monitoring, in order to resolve the problems connected to the implementation from the satellite platform, such as spatial resolution, incidence angles, temporal coverages, etc., can benefit from the use of ground-based instrumentation. This work concerns the application of ground-based SAR interferometry (GB-InSAR) to the monitoring of landslides characterized by different kinematics and diverse materials. This implementation has been realized by using the LISA (Linear Synthetic Radar) system developed at the JRC. The test sites, chosen to demonstrate the capabilities of such a technique in operational conditions, are the Ruinon rock slide in Valtellina, the Tessina earth slide in the Italian Dolomites and the Firenzuola rockslide in the Northern Appennines. The presence of independent monitoring systems within these landslides has allowed the radar measures to be validated. The LISA is a SAR system with interferometric capabilities specifically design for field applications. It is composed by a 2.8 m linear rail along which a motorised sled with two antennas is moved in order to obtain the synthetic aperture. The system can operate in the frequency band Ku (l = 1.8 cm) or C (l = 5.6 cm). Coherent SAR processing transforms raw data, acquired by the system, into a SAR images containing for each pixel information regarding the signal phase which depends on the target-sensor distance. Acquiring the data exactly from the same position (zero baseline condition), it is possible to directly relate the phase variations obtained by the interferometric analysis of consecutive couple of images to ground displacements along the line of sight of the radar instrumentations. Otherwise, by acquiring two radar datasets from slightly different positions it is possible to relate the phase variations obtained from the interferometric analysis to the topography of the observed area, providing an accurate DEM of the scene. While the first application allows to continuously follow the short term temporal evolution of the mass movements, the second one permits, by the comparison between interferometric DEM obtained in different periods, to observe the landslide evolution on a longer temporal scale. The application of these approaches to the selected test sites have demonstrated, by means of the comparison with traditionals instrumentations, the excellent precision and accuracy of the new technique. The use of such a technique, providing deformations maps of the studied area, facilitates the interpretation of the movement mechanism. Due to its non-invasive character, the good versatility in terms of suitable mass movement and the very high definition, the technique is well suited to mass movements, especially for those affecting urban area and cultural heritage.