Bridge deformations during train passage: monitoring multiple profiles using concurrently operating MIMO-SAR sensors

Sensors capable of measuring surface deformations with areal coverage and high spatial and temporal resolution are beneficial for many monitoring applications. However, such sensors are typically expensive, or their configuration cannot be adapted flexibly by the user like in case of satellite-based systems. Automotive Multiple-Input-Multiple-Output Synthetic Aperture Radar (MIMO-SAR) systems are interesting potential alternatives associated with low cost and high flexibility. In this paper, we present an experimental investigation showing the capabilities of a particular off-the-shelf, automotive radar system for structural monitoring. We analyse the accuracy of the measured line-of-sight displacements, the spatial and temporal resolution, and the impact of simultaneous coverage of the same area by two sensors of the same type. Finally, we demonstrate the MIMO-SAR system in a real-world use case measuring deformations of a railway bridge in response to dynamic load by trains passing over it. We operated two MIMO-SAR sensors simultaneously, analyse and interpret the individual interferograms and combine the data to derive the temporal and spatial distribution of vertical displacements along selected profiles. The results show that off-the-shelf automotive-grade MIMO-SAR systems can be used to quantify sub-millimetre deformations of structures and derive high-resolution time series beneficial for structural health monitoring applications.