Evaluating a global differential GPS system for hydrographic surveying

The Naval Oceanographic Office (NAVOCEANO), the U. S. Navy´s Fleet Survey Team (FST), and the National Oceanic & Atmospheric Administration (NOAA) conduct hydrographic surveys for nautical charting in accordance with International Hydrographic Organization (IHO) S-44 standards. To meet these standards, current practice requires shore stations for differential GPS control and local water level determination. A real-time global differential GPS (GDGPS) system, in which corrections are delivered by satellite, presents an opportunity to greatly simplify hydrographic operations by minimizing or eliminating shore stations. The three dimensional accuracy of GDGPS is demonstrated from static observations. The vertical accuracy of GDGPS positioning for hydrographic surveying is compared to that obtained from simultaneously acquired real-time kinematic (RTK) positioning. The accuracy of traditional hydrographic sounding reduction techniques, using water level corrections and measured heave, is also presented. The accuracy of GDGPS vertical positioning is observed to be adequate for IHO Order 1 hydrographic surveying.