Monitoring landslide displacements by using ground-based synthetic aperture radar interferometry: Application to the Ruinon landslide in the Italian Alps

Synthetic aperture radar (SAR) data are collected by a ground-based radar system forming the synthetic aperture by the sliding of the antennas on a linear rail. Coherent SAR processing converts the raw data into a complex image. The phase of each image pixel contains information on the target-sensor distance and can be exploited as a ranging tool. The interferometric technique, based on the comparison between paired and coherent SAR images taken at different times, permits the quantitative extraction of this information, thus allowing the monitoring of the morphological changes. The portable device used in this application was developed by the Joint Research Center, Ispra, Italy, specifically for measurements in the field. It is known as Linear SAR, and it is able to provide 17 GHz measurements with a 2.8 m synthetic aperture. A measurement campaign, lasting about 1 week, was performed between July and August 2000 for monitoring superficial displacements at the Ruinon landslide, a 30 million m3 rockslide in the Italian Alps. Two sequences of interferograms are presented and discussed. The interpretation of the sequences has allowed us to derive multitemporal deformation maps of the test area, thus showing the entire displacement field of those landslide sectors characterized by higher radar reflectivity and coherence. Displacement rates up to 1.2 mm h-1 have been measured with a pixel resolution of 5 m and a measurement precision of 0.75 mm. The results have been validated by using ground truth data obtained through automatic extensometers and topographic measurements. Discrepancies are limited to a few millimeters.