Millimeter-Accuracy Structural Deformation Monitoring Using Stand-Alone GPS: Case Study in Beijing, China

Abstract

Structural monitoring and engineering surveys that use the Global Positioning System (GPS) have traditionally performed using a so-called carrier-phase double-difference method in data processing. The method requires at least one reference GPS station to be continuously operated in the field during the monitoring period. The stability and data quality of the reference station would directly affect the accuracy of displacement measurements at the rover station. Furthermore, it becomes increasingly difficult to maintain “ideal” reference stations in urban environments. This article introduces a method for using stand-alone GPS units to conduct millimeter-accuracy structural deformation monitoring for poststudy or for near real-time structural health monitoring. Two years of continuous GPS observations obtained from two high-rise buildings in Beijing were used to depict the detailed method. The method comprises three steps: (1) solving GPS antenna positions with respect to a global reference frame (IGS08), (2) establishing a stable local reference frame and transforming the global positions into the local reference frame, and (3) deriving a regional seasonal model and correcting GPS-derived positional time series with the regional model. It is concluded that 2- to 3-mm horizontal accuracy and 5- to 7-mm vertical accuracy can be achieved for daily solutions with the proposed method in the Beijing metropolitan area. The key products from this study are the Stable Beijing Reference Frame (SBJRF) and the local seasonal model for GPS-derived (vertical) positional time series. SBJRF will be incrementally improved and periodically updated to synchronize with the update of the IGS reference frame. The general theory and method presented in this article could be applied to other urban areas for conducting structural health monitoring in near real time.