Analysis of Terrain Effects on DGPS and LORAN Signals

Benjamin Peterson, Dean Bruckner, Michael Danish and Peter Morris

Abstract:	The expansion of the U. S. Coast Guard's Differential GPS system to support land users, coupled with the need to upgrade aging LORAN transmitting equipment in the western U.S. and Alaska, has highlighted the need for accurate prediction of LF and MF ground wave signal strength over land paths. Traditional prediction methods, generally credited to Millington in honor of his contributions in the early 1950s, assume a smooth surface of inhomogenous conductivity. While these methods agree well with observations over flat or moderately rolling terrain, we see prediction errors of 20 dB or more in data from extremely rugged terrain in the western Continental United States, western Canada, and Alaska. Using highly detailed Digital Terrain Elevation Data (DTED) from the National Imagery and Mapping Agency (NIMA), we are analyzing terrain effects on measured signal strength. Both LORAN and DGPS data show very high correlation between Millington's method prediction errors and the integral of average slope along the path between transmitter and receiver. Initial results using a semi-empirical model that associates sloped terrain with an increased tangential component of electric field or “wave tilt” and therefore increased wave energy loss are promising.
Published in:	Proceedings of the 2000 National Technical Meeting of The Institute of Navigation January 26 - 28, 2000 Pacific Hotel Disneyland Anaheim, CA
Pages:	258 - 267
Cite this article:	Peterson, Benjamin, Bruckner, Dean, Danish, Michael, Morris, Peter, "Analysis of Terrain Effects on DGPS and LORAN Signals," Proceedings of the 2000 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2000, pp. 258-267.
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