Identifying the relationship between GPS data quality and positioning precision: Case study on IGS tracking stations

The number of Global Positioning System (GPS) tracking stations is increasing, primarily because the stations are multifunctional: in civil engineering, they can be used for precision positioning; in earth sciences, they can be used to monitor faults and earthquakes; and in atmospheric sciences, they can be applied to predict perceptible water vapor. Currently, there are more than 400 GPS stations in Taiwan, but the data obtained through such stations are not being assessed carefully. Experienced scientists and engineers examine the data in advance to see if they qualify for research purposes. However, inexperienced users can adopt poor quality data that eventually lead to inaccurate research results. Of the observation stations with receivers that were renewed between 2006 and 2008 in the International GNSS Service (IGS) Network, four stations, ZIMM, BOR1, NRC1 and NICO, were selected to be the subjects of this research. Six indices of data quality were observed to calculate the quality of data obtained before and after receiver renewal. Then, analyses were conducted to understand the relationship between the quality indices and positioning precision. Results showed that, after receiver renewal, the positioning precision of the four stations was improved by 1-19%. Therefore, positioning precision is positively affected by the six data quality indices. It was also discovered that receiver clock error was the most critical factor among the six indices. In conclusion, if data quality control can be applied to GPS tracking stations, the data obtained will be more reliable for research purposes, and the accuracy of subsequent engineering and science measurements will be improved.