Differential GPS marine navigation

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Differential GPS marine navigation

Lachapelle, G. / Hagglund, J. / Jones, H. / Eaton, M.

A GPS Marine Positioning test involving two T14100 receivers was carried out in November, 1983, by Nortech Surveys for the Canadian Hydrographic Service of the Canadian Department of Fisheries and Oceans offshore Nova Scotia's East Coast. The major objectives were, firstly, to assess the accuracy and reliability of single point GPS navigation and, secondly, to assess accuracy and reliability of differential GPS navigation using baselines of 10 to 275 kilometres. GPS positions were tested against Syledis derived positions which were accurate to three to five metres. Tests were carried out for three to five hours per day during which three to four GPS satellites could be tracked. The accuracy of both single point and differential navigation was analysed in terms of satellite geometry. During periods of relatively good satellite geometry (GDOP better than five), single point dual frequency P code positioning was generally accurate to 10 to 15 metres, while differential positioning was accurate to five metres. These differential results were obtained using a straight average of L1 and L2 P code pseudo-range measurements. The use of ionospherically corrected L1/L2 data led to inferior results in differential mode. Results using L1-only data are also presented and analysed, and related implications for C/A code differential positioning accuracies are discussed.