A Web-Based Real-Time Monitoring System for GNSS Data Quality and Integrity

SUMMARY The single base real-time kinematic (RTK) positioning technique is distance-dependent in terms of accuracy and reliability of the integer ambiguity resolution. The Network RTK (NRTK) technique has been developed to overcome this limitation, so is able to be used over longer distances than is possible with single base RTK whilst maintaining centimetre-level accuracy. This multiple reference station approach provides a precise measurement correction to the RTK positions over long baselines by interpolating errors across the reference receiver network. In order to provide reliable corrections it is necessary for the NRTK service provider to have quality and integrity monitoring mechanisms. The Department of Lands, New South Wales, operates a network of Continuously Operating Reference Stations (CORS) called ‘SydNET’ around the city of Sydney to provide real-time GPS data via the internet. It is, however, difficult to predict the variation in performance and the status of the reference stations. Therefore a scheme to monitor data streams in real-time has been proposed for dealing with the data quality control issue. This paper presents a Web-based scheme for monitoring real-time Global Navigation Satellite System (GNSS) data streams from the SydNET stations. In order to demonstrate the feasibility of this Web-based monitoring system, a prototype was developed. Networked Transport of RTCM via Internet Protocol (NTRIP) was introduced to collect data streams. The challenging part of this QC system is implementing a system that provides a real-time monitoring service of multiple stations simultaneously, and publishes quality parameters on the Web in a graphical chart with real-time updates, preferably at a 1Hz data rate. This scheme enables a visualisation of reference station performance by monitoring RTCM messages, and subsequently will be utilised to access quality control of such infrastructure, as well as supporting the Virtual Reference Station (VRS) Network RTK solution.