IMPROVEMENT OF GPS AMBIGUITY RESOLUTION USING HEIGHT CONSTRAINT FOR BATHYMETRIC SURVEYS

 

Abstract

Centimeter level of GPS positioning is required for many applications including bathymetric surveys. In order to achieve such accuracy, it is required to correctly resolve carrier phase ambiguities, i.e., a number of cycles which is not measured by a GPS receiver. The ambiguity resolution on L1 or narrow-lane band (with an effective wavelength of about 20 cm) is more difficult to achieve than that for the wide-lane band (the wavelength of the wide-lane is 86 cm), especially when the distance between the survey ship and the GPS reference station gets longer. For the bathymetric survey operations on the St. Lawrence River, the closest GPS reference station can be as far as 75 km.

This paper discusses the method of GPS phase ambiguity resolution on long baseline vectors using height constraint obtained from the digital tide gauges deployed by the Canadian Hydrographic Service (CHS) along the St. Lawrence River. In this research, the quality of the a priori height information was assessed by comparing the tide gauge reading with the GPS height when the ship was in the vicinity of a GPS reference station and a tide gauge. The success rate to instantaneously resolve the correct GPS phase ambiguities was compared for the cases, with and without height constraint, for distances between the survey ship and a GPS reference station up to about 45 km.