Concept for military surveys to IHO standards without shore stations using the real-time gipsy (RTG) global positioning system (GPS)

The Naval Oceanographic Office (NAVO-CEANO) conducts hydrographic surveys in accordance with International Hydrographic Organization (IHO) S-44 hydrographic survey standards. Presently, under most circumstances, shore stations must be established for collecting tide information that is used to define the local vertical chart datum, derive tidal correctors to reduce soundings to the chart datum, and derive harmonic constituents for future tide predictions. In addition, in many cases a shore station must be established that provides differential corrections to the GPS pseudo-ranges used by the survey vessel for accurate horizontal positioning. This current concept of operations requires clearances and permissions from national/local authorities and landowners to access and establish these shore stations. It also requires substantial efforts to establish or maintain security for both shore parties and equipment left behind at the shore stations. Recently, NAVOCEANO acquired 21 GPS receivers from NavCom Technology, Inc. with Real-Time Kinematic (RTK) and Real-Time GIPSY (RTG) capabilities and associated StarFire (TM) Wide Area Differential GPS (WADGPS) services from C&C Technologies in partnership with NavCom. NAVOCEANO has integrated these RTK/RTG receivers into its Mission Survey Systems on its fleet of survey ships and their Hydrographic Survey Launches (HSLs) and non-ship survey assets. The RTG software produces globally uniform precise GPS orbit and clock corrections. Using StarFire's satellite-based RTG signal with corrections for solid earth tide, NAVOCEANO conducted tests that indicated horizontal accuracies of 20 cm (2 sigma) and vertical accuracies of 24 cm (2 sigma) wherever the INMARSAT-C signals can be reached. These accuracies in the horizontal and vertical along with techniques to acquire the ellipsoid-chart datum separation using GPS buoys indicate a capability to survey anywhere in the littorals (outside territorial waters) to IHO standards without establishing shore stations. This paper will discuss progress on a new concept of operations under development at NAVOCEANO using the NavCom GPS technology, GPS buoys, and bottom-mounted tide gages to support the Navy's need for navigational charting and near-real-time battlespace characterization.