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Volume 1, Number 1 (2000)

Use of a Multi-Reference GPS Station Network for Precise 3D Positioning in Constricted Waterways

August 9, 2013


Numerous coastal and inland marine operations, including navigation in shallow constricted waterways require time-consuming and expensive maintenance that includes frequent precise multi-beam hydrographic surveys and dredging operations. In addition, environmental and safety concerns lead to the establishment of stringent regulations regarding the minimum under keel clearance for commercial shipping operations. The clearance is partly a function of the navigation channel charting accuracy and the ability to determine the instantaneous water level in real time. The use of real-time kinematic (RTK) GPS to provide a three-dimensional accuracy of better than 10 cm has the potential to improve the effectiveness of channel maintenance and commercial navigation. In order for RTK GPS to yield such a high level of accuracy, carrier phase observables must be used. One of the most important limitations is the requirement for short distances between the ship and shore-based fixed reference stations. With the current GPS capability, the distance should be kept to less than 15 to 20 km to assure a continuous service. Establishing reference stations with such a high density is time-consuming, logistically difficult and results in high maintaining cost and operational reliability issues. In this paper a method to substantially reduce the number of reference stations is investigated through field trials conducted along the St. Lawrence Seaway, Canada, in 1998 and 1999. The proximity of the trials to a solar maximum resulted in a very high level of atmospheric activity and provided an opportunity to examine the advantages and limitations of both the conventional and multi-reference station RTK methods under such conditions. The results of the trials show that the new approach results in a substantial improvement of up to 60%.