Abstract
Terrestrial Radar Interferometry (TRI) is a measurement technique capable of measuring displacements with high temporal resolution at high accuracy. Current implementations of TRI use large and/or movable antennas for generating two-dimensional displacement maps. Multiple Input Multiple Output Synthetic Aperture Radar (MIMO-SAR) systems are an emerging alternative. As they have no moving parts, they are more easily deployable and cost-effective. These features suggest the potential usage of MIMO-SAR interferometry for structural health monitoring (SHM) supplementing classical geodetic and mechanical measurement systems. The effects impacting the performance of MIMO-SAR systems are, however, not yet sufficiently well understood for practical applications. In this paper, we present an experimental investigation of a MIMO-SAR system originally devised for automotive sensing, and assess its capabilities for deformation monitoring. The acquisitions generated for these investigations feature a 180∘ Field-of-View (FOV), distances of up to 60 m and a temporal sampling rate of up to 400 Hz. Experiments include static and dynamic setups carried out in a lab-environment and under more challenging meteorological conditions featuring sunshine, fog, and cloud-cover. The experiments highlight the capabilities and limitations of the radar, while allowing quantification of the measurement uncertainties, whose sources and impacts we discuss. We demonstrate that, under sufficiently stable meteorological conditions with humidity variations smaller than 1%, displacements as low as 25 μm can be detected reliably. Detecting displacements occurring over longer time frames is limited by the uncertainty induced by changes in the refractive index.
Highlights
The effects determining the reliability of MIMO-SAR observations are still not completely understood. We contribute to this understanding by providing a more formal assessment of achievable performance of an automotive MIMO-SAR system by comparison with highly accurate reference measurements and measurements under stable indoor conditions and in an outdoor situation
To provide confidence intervals depending on the phase noise floor, we model displacement measurements ∆D k, k = 1, . . . , N as
The practical applicability of MIMO-SAR terrestrial radar interferometry (TRI) to structural health monitoring (SHM) still requires a better understanding of its accuracy limits and the effects impacting it
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Radar interferometry is used in a wide variety of monitoring applications ranging from small-scale phenomena like landslides to assessing large mass-movements as occurring e.g., after earthquakes [1,2,3,4]. Measurements are extracted from the relative attenuation, delay, and frequency shift of signals radiated by a transmitting antenna (TXA), reflected by an object, and detected by the receiving antenna (RXA). Radar interferometry uses the phase information of the complex received signal to derive metric displacements in line-of-sight (LOS), see Section 2.4 for more details
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