En-Route Coverage Validation and Calibration of Loran-C with GPS

G. Lachapelle, B. Townsend

Abstract:	The operation concepts of Loran-C are presented. The North American coverage of the system, together with a qualitative summary of its user population are discussed. The performance of the 100 kHz system is then described in terms of repeatable and absolute accuracy. Error sources, which are divided into two groups, are quantified with the use of North American field examples. The first group consists of the time-varying errors and includes weather effects, atmospheric noise, and transmitter’s and receiver’s errors. The second group consists of the errors which are practically constant in time and includes the effects of conductivity and topography. Time-varying weather effects can result in position errors of up to 50 m with higher extremes. The effects of conductivity and topography on absolute or relative positions are much higher and reach several hundred meues in mountainous areas. The effects are however constant and can be determined directly by field comparisons with GPS-derived positions, these being unaffected by the above phenomena. The LORCAL2 (LORan CALibration at The University of CALgary) system being developed for the en route calibration of Loran-C using differential GPS (DGPS) is described. The configuration consists of two major parts, namely a vehicle mounted segment and a stationary segment for differential operation. The vehicle segment includes a high performance Ashtech LD-XII GPS receiver, a PC-based recording system, and a Megapulse Accufix 520 receiver which measures time differences, field strength and envelope-to-cycle difference. Additional Loran-C receivers can be added to the vehicle segment to test en route receiver performance. The stationary segment consists of a second LD-XII GPS receiver and recording system and, optionally, a Loran-C receiver for DLC performance analysis. The DGPS part of the system yields a constant position accuracy of 2 to 5 metres at normal cruising speeds. Initial static tests conducted during Summer 1989 in the coastal range of British Columbia, where position distortions can reach several hundred metres over distances of 20 km, are reported. Future applications of LORCAL2 are described. These include calibration of the Canadian coverage of the North Central U.S. Chain, which is due to become available in early 1991, detailed analysis of the secondary phase lag distortions at the prairie/mountain boundary of Western Canada, and study of the spatial secondary phase lag variation over the Canadian Rockies, this being of interest to Loran-C air navigation users.
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	199 - 205
Cite this article:	Lachapelle, G., Townsend, B., "En-Route Coverage Validation and Calibration of Loran-C with GPS," Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990), Colorado Spring, CO, September 1990, pp. 199-205.
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