Abstract
Although major breakthroughs have been achieved during the last decades in the use of Global Positioning System (GPS) technology on structural health monitoring, the mitigation of the biases and errors impeding its positioning accuracy remains a challenge. This paper tests an alternative approach that can increase the reliability of the GPS system in structural monitoring by using the spectral content of the signal-to-noise ratio (SNR) of GPS signals to detect frequencies of antenna vibrations. This approach suggests the potential of using SNR data analysis as a supplement to low-quality positioning solution or as a near real-time alert of excessive vibration proceeding the position solution calculation. Experiments, involving a GPS antenna subjected to vertical vibrations of 0.4- to 4.5-cm amplitude at a range of frequencies between 0.007 and 1 Hz, examine the dynamic multipath-induced SNR response corresponding to the antenna motion. Synchronised fluctuations in the SNR time series were observed to reflect the antenna motion and their spectral content to include the frequencies of motion. SNR records from the GPS monitoring of the Wilford suspension bridge were used to validate the SNR sensitivity to controlled vibrations of the bridge deck. The natural frequency of 1.64 Hz was extracted from SNR measurements using spectral analysis on a 6-mm amplitude vibration, and the frequency of the semistatic displacement (∼0.02 Hz) was revealed in the SNR records permitting, after appropriate filtering, the estimation of a few millimetre semistatic displacement from the GPS time series without the need for any other sensor.
Highlights
In the last decade the potential for using the Global Positioning System (GPS) in Structural Health Monitoring (SHM) has been revealed through experimental studies, which proved its ability in monitoring oscillations of sub-cm level displacement and high-rate frequencies [1, 2, 3, 4, 5, 6], and applications to real monitoring of bridges [7, 4, 8] and buildings or towers [9, 10, 11], where the GPS monitoring was successfully used to estimate the main characteristics of the structures response
A new approach on the utility of the signal-to-noise ratio of GPS signals was proposed for GPS structural monitoring applications, focusing on the retrieval of frequencies of motion and the detection of excitation intervals
The real bridge monitoring application showed the potential of the signal-to-noise ratio (SNR) of the GPS signal to reflect high- and low-frequencies of motion in the more complex situation of a real structural response
Summary
In the last decade the potential for using the Global Positioning System (GPS) in Structural Health Monitoring (SHM) has been revealed through experimental studies, which proved its ability in monitoring oscillations of sub-cm level displacement and high-rate frequencies [1, 2, 3, 4, 5, 6], and applications to real monitoring of bridges [7, 4, 8] and buildings or towers [9, 10, 11], where the GPS monitoring was successfully used to estimate the main characteristics of the structures response. The multipath-induced oscillations on the signal-to-noise ratio (SNR) of the GPS signals have been used to map the multipath environment surrounding the geodetic antenna [25], retrieve soil moisture [26, 27], monitor vegetation growth [28] and estimate sea and snow level variations [29, 30] These applications are based on the SNR sensitivity to carrier phase multipath. The above principle of GPS-reflectometry is adapted to GPS structural monitoring applications, by reversing the given conditions and parameters (variable satellite elevation angle and reflecting objects, fixed GPS antenna etc.) and analysing the SNR variations in GPS satellite signals caused by multipath interference to detect frequencies of motion of structures. The SNR data collected from the GPS monitoring of the Wilford Bridge, a well-monitored pedestrian suspension bridge [7, 31, 32], were used to test the utility of SNR in identifying the natural frequency of the bridge and the semi-static displacement in two excitation events
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