Enhanced loran for maritime harbor entrance and approach

The U. S Coast Guard and Federal Aviation Administration are cooperating in a major effort to define and analyze the performance of a new Enhanced Loran system as a backup for GPS provided services. Each transportation mode has defined requirements that the new Enhanced Loran must meet to be acceptable in the radionavigation mix of systems. The USCG developed a set of requirements for Loran maritime navigation in terms of availability, accuracy, integrity and continuity for the Harbor Entrance and Approach (HEA) region. The USCG chaired Loran Accuracy Performance Panel (LORAPP) is spearheading the research and a proof-of-concept project into Loran meeting maritime navigation needs. This paper examines Loran\u27s ability to meet HEA requirements. The accuracy component is considered the greatest challenge for Enhanced Loran to overcome in the maritime environment. The paper explores how the Loran system can correct for signal propagation variations by broadcasting differential corrections similar to the DGPS system. The differential corrected Loran, or dLoran, uses a 32-state Pulse Position Modulation scheme on one additional pulse in the Loran group. The data pulse is used to broadcast a propagation correction to a nominal Additional Secondary Factor (ASF) value derived from multiple land-base monitor sites. A detailed analysis of the communication scheme is given as it relates to the data channel using the 100kHz sine wave Loran signal. The ASF correction value is composed of a spatial and temporal component. We examine the process to survey desired waterways creating a spatial grid for each transmitter station in view. The waterway grid is correlated to a land-base monitor station that measures the temporal component. In broadcasting the temporal variations, the shipboard receiver then moves the entire grid up/down to match the temporal correction