Early warning system for the detection of unexpected bridge displacements from radar satellite data

Several hundred satellites are monitoring our planet every day, some of which are able to measure subtle ground movement. Satellites that carry synthetic aperture radar (SAR) sensors are capable of providing high-resolution weather-independent imagery of the Earth. By taking several images of an area of interest at different times and analyzing them with advanced processing techniques such as interferometric SAR (InSAR), millimeter-level motion on ground structures can be detected and measured. Ground motion maps have been validated for several scenarios over the past 20 years utilizing Earth Observation (EO) technology. This paper presents InSAR basics and the methodology to apply this mature EO technology to bridges with a focus on the interpretation and validation of satellite data and their use for 3D visualization and early warning of unexpected bridge displacements. The concept of thermal sensitivity and its use to monitor bridge behavior is introduced. Two case studies are provided to illustrate and validate the application, and specific calculation methods are proposed to determine the extent of thermal movement for given types of bridges. Finally, a new 3D visualization tool that incorporates processed satellite data is briefly presented, which will serve in future development phases as a platform for bridge movement assessment and early warning to identify and flag abnormal bridge displacements, and to help avoid failures.