Loran-C Implementation in the Coastal Confluence Zone

Abstract The Secretary of the Department of Transportation announced the selection of Loran-C as the U.S. Government sponsored radio navigation system to serve the Coastal Confluence Zone (CCZ) on May 16, 1974. This paper provides information concerning the implementation of Loran-C in the CCZ. It will address chain configurations/ reconfigurations (as appropriate), coverage, accuracies and operational schedules. The expanded Loran-C grid will permit navigation fixes to 1/4 NM or better 95% of the time throughout the CCZ and use of the signals in a repeatable mode will permit returning to within 100 ft of a previously determined position throughout much of the CCZ. Detailed information concerning Loran-C coverage characteristics in the Gulf of Mexico and the Western Coast of North America will be discussed, including representative examples of near shore accuracies. A status report on the West Coast/U.S. Canadian/Gulf of Alaska stations scheduled to become operational January 1, 1977 will be made during the presentation. INTRODUCTION Loran-C is a pulsed hyperbolic radio aid of navigation operating in the frequency band of 90–110 kHz. Specially designed receivers make time difference comparisons of the received signals which are then translated to a navigational fix by utilizing either lines of position (manual with charts) or direct coordinate conversion to latitude/longitude (more sophisticated receivers). Due to the signal format and the low frequency of transmission, Loran-C transmitting stations can be separated by hundreds of miles, thus only 22 are needed to produce coverage with 1/4 NM accuracy in the CCZ A generalized explanation of the system is contained in the LORAN-C USER HAND BOOK. Since the May 19"Z4 announcement, much has been done to implement the coverage of Loran-C in the CCZ. The schedule, published in the Annex to the National Plan for Navigation, provided for a three phase implementation West Coast/Gulf of Alaska in 1977, Gulf of Mexico/ East Coast reconfiguration in 1978 and completion of Great Lakes coverage on 1980. Sites have been selected, Environmental Impact Statements (EISs) have been filed and land has been reserve for all stations with the sole exception of the Great Lakes site (currently referred to as International Falls, MN). A diagram showing both existing and proposed coverage is shown in Figure 1. It should be noted that this diagram differs slightly from those produced in 1974 because site positions reflect final locations. Another item to be noted is that the diagram is for 1/3 Signal to Nosie (S/N) ratio rather than the 1/10 ratio used in the development of N.D. 5130. This paper will address all three phases of the implementation, but with emphasis on the Gulf Coast/East Coast reconfiguration phase. WEST COAST/GULF OF ALASKA Three Loran-C chains will be established and eight new stations will be constructed between December 1975 and January 1977. The most difficult phase to date was that of land acquisition. Locating a 200 acre site in a suitable environment without creating significant interference to existing developments proved to be a real obstacle and over 60 sites had to be considered.