Monitoring the quality of GPS station coordinates in real time

This paper evaluates various statistical process control algorithms for monitoring the quality of GPS station coordinates in real-time kinematic applications. Real-time detection of small but persistent shifts in GPS coordinates is critical for applications requiring automatic and reliable results in deformation monitoring. Examples include monitoring of dams, high-rise buildings, bridges, tectonic movements, landslides and so on. The conventional cumulative sums (Cusums), the robustified and self-starting Cusums, the adaptive Cusum and the exponential weighted moving average are some of the control charts applied to real-time-kinematic (RTK) data in field experiments. All control charts have been evaluated for their effectiveness in detecting an actual but intentional deformation shift of at least 0.5 standard deviations from a target mean. The observations used in testing these control charts had initially been assumed to be independent and follow a normal distribution, but later, their serial correlation was taken into consideration. These results show that the self-starting but robustified Cusums as well as the exponentially weighted moving average charts are suitable and efficient tools in monitoring quality in the RTK data. All presented control charts are implemented as modules in a software package being developed by the Technical University of Crete.