Vessel heave determination using the Global Positioning System

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This thesis investigation shows how the precise carrier-phase measurements available from the Global Positioning System in differential mode may be used to monitor the vertical motion of a ship - called heave. A model to utilize GPS observations in combination with ship attitude measurements has been devised and implemented. This model has been incorporated into a hydrographic navigation system being produced by Nortech Surveys (Canada) Inc. for the Canadian Hydrographic Service [Rapatz and Wells, 1990]. Testing of this model using a static data set indicates accuracy levels in order of five centimeters or less. Comparisons of GPS measured heave with commercial heave sensor data during a ship cruise 100 kilometres offshore of Shelburne, N.S. reinforces this initial accuracy estimate. The investigation illuminates some of the advantages, disadvantages and problems with using GPS for heave measurements and recommends areas of further research. The final conclusion is that used appropriately, GPS has the capability of accurately mesuring vessel heave, even under circumstances in which commercial heave sensors may be incapable.