Methodology for deploying ASF monitor sites in South Korea

There has been interest in recent years in backup systems in case of the loss of GPS in South Korea. The Ministry of Maritime Affairs and Fisheries had conducted the feasibility study using DGPS beacon signal and recently Ministry of Land, Transport and Maritime Affairs started to examine eLoran (enhanced Loran) system, especially in the harbor entrance and approach (HEA). In order to meet this HEA accuracy requirement, user receivers must employ additional secondary factors (ASFs) in calculating the user´s position. ASFs are time adjustments that modify the receiver´s times of arrival (TOA) to account for propagation over non-seawater paths. As these ASFs vary both spatially and temporally, both variations need to be compensated for to meet the HEA accuracy targets. In the proposed eLoran system, the spatial variations are accounted for through the use of grids of ASF values that are known by the receiver a priori. The temporal variations are accounted for by operating in differential mode; specifically, a nearby reference monitor station estimates and broadcasts the temporal changes in the ASFs relative to the published spatial grids. The U.S. Coast Guard Academy is conducting research and proof-of concept demonstrations of the ability of enhanced Loran to support the HEA navigational requirements. In this paper, we outline the methodology to import and deploy the eLoran system in South Korea; especially, ASF grid development techniques and location of monitor sites and operations in Busan harbor referring to the efforts of the United States.