Simultaneous estimation of dam displacements and reservoir level variation from GPS measurements

GPS has been widely applied to monitor displacements using direct measurements. Even conventional ways using direct measurement can achieve millimeter level (better than 1mm in horizontal and 2mm in vertical component) accuracy displacement, the causative loads such as hydraulic thermal loads always have to be obtained by other sensors or methods. This paper proposes a novel method to derive reservoir level variation data with displacement estimation simultaneously for the mechanism explanation of deformations. This method is based on multipath theory for specular reflections and the use of Signal-to-Noise Ratio (SNR) data, rather than direct measurements in GPS. We took data from an existing GPS monitoring system which has been set up on the Xilongchi Dam in Shanxi Province, China. A whole year of data from the sites located beside the reservoir was used to conduct the experiments. The result indicates that the water level variation daily time series estimated with SNR measurements can be achieved to centimeter level. The correlation between the estimated value and the daily records can even reach up to 0.98. It can be concluded that the GPS-based system designed by this paper can monitor displacements and reservoir level synchronously, and GPS is also confirmed to be a viable tool for both the monitoring of dam displacements and a reservoir water level indicator.