Marine DGPS Using Code and Carrier in a Multipath Environment

G. Lachapelle, W. Falkenberg, D. Neufeldt, P. Kielland

Abstract:	The operational constraints of DGPS in the marine environment are reviewed. In particular. the problem of recovering the initial baseline, i.e., the initial coordinate differences between the shore-based monitor station and the vessel is discussed. The recovery of this initial baseline requires the use of code measurements. However, the relative position changes of the vessel are best determined using the relatively more accurate carrier phase measurements. A procedure to combine both code and carrier phase measurements to achieve the above goal in an operationally acceptable manner is discussed. An external accuracy of <5 m (95% confidence level) can generally be obtained with this method. However, code measurements can be affected significantly by multipath, which can decrease the reliability of the above method to an unacceptably low level. Examples of code multipath obtained under field conditions show systematic effects with peak to peak amplitudes of 20 m and periods of several minutes. Two multipath counter-measures are discussed and tested, namely the use of a RF absorbent ground plane made of carbon impregnated foam at the monitor station and the use of parallel filters at both the monitor and mobile stations. These methods reduce the effect of code multipath to a level sufficiently low to maintain the accuracy quoted above in a high multipath environment.
Published in:	Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989) September 27 - 29, 1989 The Broadmoor Hotel Colorado Spring, CO
Pages:	343 - 347
Cite this article:	Lachapelle, G., Falkenberg, W., Neufeldt, D., Kielland, P., "Marine DGPS Using Code and Carrier in a Multipath Environment," Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989), Colorado Spring, CO, September 1989, pp. 343-347.
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