Stability Monitoring of Bridges via Dual Frequency Terrestrial Radar Measurements

Abstract

The monitoring of the stability of bridges is a technical challenge that, in recent years, has been tackled by means of real aperture radar interferometers. Such technique extracts, for each radar range cell, the time series of the received signal phase, which is related to the displacement of the phase center of the radar range cell. By analyzing the displacement time series of the reflection points located on the monitored structure it is possible to extract the vibrational frequencies and amplitudes of such points. In this work we employ two different radar systems, working at 17 and 24 GHz respectively, to analyze the vibrations of a railway bridge in static conditions located in Galicia, North-Western part of Spain. The radar trials were realized by locating the radar systems at three different locations, one under the bridge with the radar Line-of-Sight parallel to the bridge longitudinal axis, one at the right and one at the left of the bridge. Such geometrical diversity allows to detect multiple vibrational modes, both on the vertical and tangential directions. Tangential and vertical modes are detected with amplitudes of tens microns. The results obtained using the two radar systems show a quite good agreement and are validated against accelerometer acquisitions, which is aimed at demonstrating the suitability of radar interferometers to measure bridge vibrations. The improvement of some performance of the radar survey using the higher frequencies radar is also discussed.