Assessment of Spaceborne SAR Micro-Motion Measurement for Vibration-Based SHM

Remote sensing methods for vibration-based structural health monitoring (VBSHM) are gaining interest given the benefits of non-contact sensing for this application: broader spatial coverage, easier measurement access to structures such as bridges, and cost savings from reducing the need for embedded sensor networks. Vibration measurement using micro-Doppler synthetic aperture radar (MDSAR) is an emerging technique enabling the measurement of structural vibrations from synthetic aperture radar (SAR) satellite data, exploiting recent advancements in high-resolution X-band radar imaging. This paper presents a detailed metrological assessment of MDSAR – using processing based on the pre-existing subpixel offset tracking (SPOT) concept as a representative method – to evaluate its applicability to VBSHM. Measurements are made from real SAR images of vibrating targets with synchronous ground truth data. The results verify that the technique can be used to measure target motion time-histories with dynamics relevant to SHM, namely different modulations with frequencies from 1 to 4 Hz, and radial RMS displacement amplitudes from 10.43 to 0.10 mm. These results pave the way for future measurements of infrastructure.