GPS differential positioning technologies for hydrographic surveying

The real-time GPS (Global Positioning System) differential kinematic positioning techniques developed for shipborne surveying applications for the Canadian Hydrographic Service are presented. These include pseudorange and carrier-phase integration methods, cycle slip and multipath counter-measures, local clock constraint techniques, and roll, pitch, and heave estimation algorithms. Major factors considered in the development and implementation of these techniques are accuracy, reliability, and real-time operation. Preliminary results obtained from a recent controlled kinematic experiment to assess the affect of multipath are presented. It is concluded that the GPS differential positioning technologies developed for the Canadian Hydrographic Service have resulted in external accuracies ranging from 50 cm to 5 m in land, shipborne, and airborne modes