A patent is in the works for this hydrographic navigation system.

A new GPS-based hydrographic navigation system has been developed, which eliminates tidal uncertainties of hydrographic surveys in coastal areas. The Real-Time Kinematic (RTK) GPS Tides concept was developed at the U.S. Army Corps of Engineers’ Engineer Research and Development Center’s Topographic Engineering Center (TEC) in Alexandria, Va. A patent is being pursued. The highly accurate system uses a land-based GPS reference station operating in a carrier differential mode of operation. Radio signals transmit carrier differential information to ships in the approach channels, enabling properly equipped GPS receivers onboard to produce centimeter-level, three-dimensional positions every second. This position information is coupled with the ship’s keel distance below the GPS receiver to determine the keel height above a predefined grid of the navigation channel and specifically the project depth or the bottom of the navigation channel. The bottom of the navigation channel should be slightly above the actual bathymetry. If it is not, a shoal has formed in the channel, and dredging is required to remove the shoal.