The St. Lawrence River flows 3,800 kilometers from the Great Lakes to the Atlantic Ocean, carrying some 36 million metric tons of cargo through the Montreal-Lake Ontario section in the course of a typical nine-month navigation season. The U.S. locks at Messina, New York, see some 3,167 vessel transits during the same period. Since it is a limited-depth waterway carrying as much traffic as it does, the St. Lawrence River needs to be managed in a way that takes into consideration the dual priorities of safety and efficiency. This task includes figuring out the optimal uses for the river in terms of vessels, speeds and traffic without permitting unnecessary safety hazards. In the heavily trafficked 300-kilometer Laurentian section of the river, dredging operations are essential. Ice forms during the winter and flows downstream in spring, displacing huge amounts of rock and debris that, in turn, significantly alter water depth in spots. Those depth changes require constant vigilance to ensure ships' safety. Nearly four years ago, the Canadian Coast Guard began to look for a real-time kinematic Global Positioning System solution that would give vessel positioning data as well as greater overall accuracy, and would take into account the hydrodynamic effects which the old system could not measure. After a demonstration that achieved real-time kinematic (RTK) initialization at 65 kilometers from the base station, the officials selected Thales Navigation's Long Range Kinematic (LRK(trademark)) solution. The system takes full advantage of dual-frequency Global Positioning System technology while reducing initialization times to just a few seconds. Importantly, the system maintains optimal real-time positioning accuracy to within a centimeter at a range of up to 40 kilometers, even with a reduced number of available satellites. "The three-dimensional position of the survey vessel is obtained in real-time, thanks to the system's LRK feature," Marceau said. "The position is expressed in the WGS84 geodesy datum and can be converted to the chart datum with the help of a so-called seamless datum." The seamless datum is a grid model designed by the Canadian Coast Guard and the Geodetic Survey of Canada that helps calculate the differences between the WGS84 datum and the chart datum, he explained. The overall system, implemented in late 2001, has allowed the Coast Guard to begin to phase out the tide gauge system.


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    Titel :

    St. Lawrence River marine survey via global positioning system


    Beteiligte:
    Jaouen, R. (Autor:in)

    Erschienen in:

    Sea Technology ; 44 , 6 ; 49-51


    Erscheinungsdatum :

    2003


    Format / Umfang :

    3 Seiten



    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch




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