Remote Sensing of Landslide Motion with Emphasis on Satellite Multitemporal Interferometry Applications: An Overview

Abstract Landslide hazard reduction can benefit from increased exploitation of affordable remote sensing systems, with a focus on early detection of ground deformations, long-term monitoring, and possibly early warning of catastrophic failure. Among several innovative space-based remote-sensing techniques, synthetic aperture radar (SAR) and multitemporal interferometry (MTI) hold the most promise, because of its capacities and strengths: (1) wide-area coverage (tens of thousands of square kilometers) combined with a high spatial resolution (up to 1 m for the new generation of radar sensors) and hence the possibility of conducting multiscale investigations with the same data sets (from regional to slope-specific); (2) systematic, high-frequency (from a few days to weeks) measurements over long periods (years); (3) a high precision of surface displacement measurements (millimeters–centimeters) only marginally affected by poor weather conditions; (4) cost effectiveness, especially in the case of long-term, large-area investigations (catchment to regional scale); and (5) integration of landslide monitoring (based on new satellite imagery) with retrospective studies (archived imagery) to investigate slope failure history or landslide reactivation/acceleration processes. We illustrate the potential of MTI and explain how it can be used to detect and monitor landslide motion by considering applications in areas with a broad range of geomorphic, climatic, and vegetation conditions. The chosen examples of local-to-catchment-scale MTI case studies focus on unstable hill slopes and landslides in the Apennines (Italy), the European Alps, and on the island of Haiti. The potential of MTI is further assessed by also considering the strengths and limitations of other innovative applications of remote sensing in landslide monitoring, which rely on several recent or emerging techniques: Corner Reflector SAR interferometry, which exploits artificial targets installed on the ground and radar satellite imagery; ground-based InSAR; air- and ground-borne Light Detection And Ranging (LiDAR); and air/space-borne image matching. These applications, however, typically focus on single failed slopes and their use for regular, wide-area mapping of ground surface changes is at present economically prohibitive. We foresee that MTI will make landslide monitoring more effective and more affordable in more situations, and will become increasingly more important in cases where little or no conventional monitoring is feasible (e.g., remote locations and limited funds). We also expect that the role of prevention in slope hazard management can be enhanced by capitalizing more on the presently underexploited advantage of MTI, that is, its ability to regularly provide vast amounts of quantitative information on slope/ground stability conditions in large areas currently unaffected (or thought to be unaffected) by landslides, but where the terrain geomorphology and geology may indicate potential for future failures. Finally, we stress that high spatial and temporal resolution satellite remote sensing of ground deformations open new possibilities for landslide research and for more timely and detailed slope hazard assessment.