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APPENDIX C 171 2005.49 Several promising technologies are currently undergoing extensive testing, but an operational system is not expected to be in use until 1999 or beyond.50 U.S. Coast Guard DGPS Service The Coast Guard currently is establishing a DGPS network that will for the first time, meet the extremely accurate navigation requirements of commercial and recreational mariners in our nation's environmentally sensitive harbor and harbor approach areas.51 When fully operational in 1996, the system is expected to reduce the number of navigation-related grounding and collision incidents by 50 percent over existing navigation methods. A total of 50 reference stations will be installed at sites along the coastal United States, the Great Lakes, Puerto Rico, Alaska, and Hawaii. Each site will use a marine radiobeacon to broadcast differential corrections and integrity information in the RTCM SC-104 message format.52 The radiobeacon signals can be received by a device about the size of a computer modem with an antenna similar in size to one used by a GPS receiver. By applying the broadcast differential corrections to a GPS position solution in real-time, a user can achieve navigational accuracy as good as 1.5 meters (2 drms) up to 460 kilometers (250 nautical miles) from the reference station.53 The Coast Guard hopes to eventually meet the stringent accuracy requirements of inland waterway navigation with their DGPS network as well. In order to achieve this goal, the Coast Guard has entered into a Memorandum of Agreement with the Army Corps of Engineers that will expand DGPS service throughout the navigable waters of the Mississippi River and its tributaries.54 NOAA Continuously Operated Reference Stations The goal of NOAA's Continuously Operated Reference Station (CORS) program is to implement a single, consistent set of federally funded DGPS reference stations that would provide GPS data to all users in a single common format with continuous monitoring of 49 Federal Aviation Administration, FAA Draft GPS Transition Plan, 1994. pp. IV-5 and IV-6. 50 Federal Aviation Administration, FAA Draft GPS Transition Plan, pp. 11-29. 51 U.S. Coast Guard, U.S. Coast Guard GPS Implementation Plan, June 1994. 52 The Radio Technical Commission Maritime (RTCM) SC-104 data message is very similar to the GPS navigation message and uses the GPS parity algorithm. Radiobeacons broadcast this message at frequencies between 285 and 325 KHz. 53 U.S. Coast Guard, U.S. Coast Guard GPS Implementation Plan. 54 U.S. Coast Guard, U.S. Coast Guard GPS Implementation Plan.
