Advances in RTK and Post Processed Monitoring with Single Frequency GPS

Abstract

In many monitoring applications, such as tall buildings, bridges and volcanoes, GPS offers significant advantages over other measurement techniques. GPS allows a high rate of measurement and long distances between the control and monitoring points and does not require line of sight to the control points. The traditional dual-frequency GPS receivers used in surveying are high accuracy but also relatively high cost per monitored point and therefore often prohibitive for the deployment of a GPS monitoring network. Until recently, cost effective L1 sensors and software have not been able to provide the necessary level of accuracy and reliability. A new solution from Leica Geosystems provides real time and post processed RTK positioning with L1 only GPS receivers for monitoring applications. The solution is built on Leica's RTK positioning algorithms, which have proven world-class performance in the surveying industry. The positioning algorithm used in the Leica GX1230 RTK GPS receivers has been implemented in the GPS Spider reference station software and tuned for monitoring applications, giving GPS Spider the capability to compute real time ambiguity fixed solutions for single and dual frequency GPS in addition to its powerful site configuration and data management tools. A direct link has been made between GPS Spider and Leica GeoMoS, Leica's geodetic monitoring software, so that users can combine GPS with the sophisticated terrestrial measurement capabilities of Leica’s robotic total stations and utilize GeoMoS’s flexible messaging and data analysis capabilities. In addition the RINEX data logged by GPS Spider may be automatically post processed for users with the highest accuracy and reliability requirements. This paper presents results from the system, including using a new ambiguity resolution technique, called quasi-static initialisation, designed for single frequency monitoring. Results from L1 processing are compared to a dual frequency solution in terms of accuracy and reliability. Data was collected with a range of baseline lengths up to 20km in medium multipath environments, typical of many monitoring applications. The L1 system is shown to have remarkable accuracy and reliability, especially in terms of price versus performance.