Precision Loran-C Navigation on the St. Marys River

Abstract

The united states coast guard has performed a successful demonstration on the St. Marys River of the feasibility of precision navigation in restricted waterways using Loran–C as a prime sensor. The St. Marys River, located in northern Michigan near the city of Sault Ste. Marie, serves as the only water shipping route connecting Lake Superior with the rest of the Great Lakes and the St. Lawrence Seaway. The 65–mile river, which is traversed by iron ore carriers up to 1000 feet long and 105 feet wide, has channels as narrow as 300 feet. A special four–station Loran–C mini–chain was established by the Coast Guard in 1976 to provide an all–weather, year–round navigation capability. Initial tests were performed on USCG vessels to determine the feasibility of using Loran–C as a navigation aid on the St. Marys River. The navigation accuracy objective was a maximum cross–track error on the order of 25 feet using Loran–C data integrated with gyrocompass heading information. This paper describes the operational environment, Loran–C mini–chain, shipboard user equipment configuration and software approach, and results of the feasibility tests. Various statistical performance parameters are presented on the Loran–C signals, static accuracies, and dynamic navigation performance. The results of the USCG feasibility tests to-date indicate that Loran-C offers great promise for high-precision navigation.