Geomatics Engineering at The University of Calgary. J. Stephen is a ... several years with the introduction of Marine Differential ... free from blunders. .... instead because the cross-track error is of primary concern .... -90-75-60-45-30-15 0 15 30 45 60 75 90. 0. 10. 20 ..... Leick, A., 1995, GPS Satellite Surveying, 2nd Edition.
Testing and Analysis of Reliability Measures for GNSS Receivers in the Marine Environment S. Ryan, J. Stephen, and G. Lachapelle Department of Geomatics Engineering The University of Calgary
BIOGRAPHIES Sam Ryan holds a BEng (1992) from Memorial University, St. John's, Newfoundland and is an Electronic Systems Engineer in the Technical and Operational Services Directorate of the Canadian Coast Guard. At present he is on educational leave to obtain an MSc. in Geomatics Engineering at The University of Calgary. J. Stephen is a MSc. student in the Department of Geomatics Engineering, The University of Calgary. He obtained a BSc. in Geomatics Engineering from that department in Spring 1997. Dr. Gérard Lachapelle is Professor and Head of the Department of Geomatics Engineering where he is responsible for teaching and research related to positioning, navigation, and hydrography. He has been involved with GPS developments and applications since 1980. ABSTRACT Marine navigation has been revolutionized by the deployment of marine radiobeacon DGPS systems. While most of the precision requirements for marine navigation can now be met with marine DGPS, the reliability of the user’s position is often ignored. The reliability of the DGPS corrections is ensured through the use of redundant shore based equipment and real time integrity checks. However, reliable corrections do not guarantee a reliable user’s position since user blunders can still occur. The reliability of the user’s DGPS position is addressed in two parts. First, software simulations are conducted to evaluate the reliability improvement when DGPS is augmented with single point GLONASS, differential GLONASS, differential geostationary satellites, and height and clock constraints in constricted waterways. These simulations demonstrate that DGPS must be augmented with at least one differential satellite system in order to ensure reliable positioning. Second, the reliability performance of four representative marine user receivers is tested using a differential GPS signal simulator. None of the receivers tested employed a reliability algorithm, thereby allowing the multipath blunders to contaminate
the user’s position. Although the higher end receivers mitigated the multipath blunders, gross position errors still occurred. Therefore in addition to augmenting DGPS, it is shown that a simple reliability algorithm can dramatically improve user navigation performance. INTRODUCTION Marine navigation has been revolutionized over the past several years with the introduction of Marine Differential GPS (DGPS) systems by both the Canadian and United States Coast Guards. The levels of service being provided by the two Coast Guards are essentially identical, with both systems using Ashtech reference stations (based on the Ashtech Z-12™ receiver). The horizontal accuracy specification for both systems is 10 m (95% of the time), however meter level positioning accuracies can be achieved with high end GPS receivers. Table 1 lists some of the marine positioning accuracy requirements. Table 1 Marine Positioning Accuracy Requirements Applications
2DRMS Accuracy
Safety of Navigation [FRP, 1996] Ocean Phase
1.8 – 3.7 km
Coastal Phase
460 m
Harbor and Harbor Approach
8 – 20 m
Inland Waterways
2–5m
Other Desirable Requirements [Lachapelle, 1997] Placing Aids to Navigation
