High resolution satellite multi-temporal interferometry for monitoring infrastructure instability hazards

Advanced remote sensing techniques are now capable of delivering more rapidly high quality information that is sufficiently detailed (and cost-effective) for many engineering applications. Here we focus on synthetic aperture radar (SAR), multi-temporal interferometry (MTI). With radar satellites periodically re-visiting the same area, MTI provides information on distance changes between the on-board radar sensor and the targets on the ground (e.g., human-made structures such as buildings, roads and other infrastructure). The detected distance changes are thus interpreted as evidence of ground and/or structure instability. In settings with limited vegetation cover, MTI can deliver very precise (mm resolution), spatially dense information (from hundreds to thousands measurement points/km 2) on slow (mm-cm/year) deformations affecting the ground and engineering structures. Radar satellites offer wide-area coverage (thousands km 2) and, with the sensors that actively emit electromagnetic radiation and thus can "see'' through the clouds, one can obtain deformation measurements even under bad weather conditions. We illustrate the potential of high resolution MTI and explain what this technique can deliver to assist in infrastructure instability hazard assessment. This is done by presenting selected examples of MTI applied to monitor post-construction behavior of engineering structures. The examples are from Italy and include: an earthfill dam, an off-shore vertical breakwater built to protect an oil terminal, city buildings and a highway. We also stress that the current approach to the assessment of instability hazard can be transformed by capitalizing more on the presently underexploited advantage of the MTI technique, i.e., the capability to provide regularly spatially dense quantitative information for large areas where engineering infrastructure may currently be unaffected by instability, but where the terrain and infrastructure history (e.g., aging) may indicate potential for future failures.