DMAHTC Support to National Ocean Survey Loran-C Charting

Abstract

The selection of Loran-C as the primary radionavigation system for the United States Coastal Confluence Zone (CCZ) requires, by joint agreement, that the Defense Mapping Agency Hydrographic/Topographic Center provide corrections to Loran-C lattices overprinted on National Ocean Survey (NOS) charts. Additional Secondary Factor (ASF) Corrections to warp the lattices are necessary if the system is to meet ¼ nautical mile or better positioning accuracy required by the Department of Transportation (DOT) and specified in the 1977 National Plan for Navigation. The Coast Guard, which has statutory responsibility for the Loran-C Radionavigation System, expects it to be the principal aid to navigation for civil use in the CCZ until the year 2000. For Department of Defense (DoD) purposes the system will be replaced eventually by the NAVSTAR Global Positioning System (GPS). This paper reviews future plans for refinement of the techniques to compute ASF corrections, as well as past and present computational methods. In addition, it examines the status of the Loran-C Radionavigation System and the status of NOS charts which support the system. The U.S. Coast Guard has surveyed critical areas in the CCZ to verify the accuracy of Loran-C NOS chart lattices. An example survey in the offshore area of the west coast is depicted and discussed.