ASF Correction Within an Integrated Navigation System of Loran-C / RDSS

Hongqing Chen and Xiuming Chen

Abstract:	Two geostationary satellites of the Radio Determination Service System (RDSS) can be constructed as a new integrated navigation system combined with two Loran-C stations. A common time reference used for navigation can be formed of the atomic clocks of the RDSS with the Loran-C system by comparing those clocks. It can also be measured and transmitted the time difference between the transmitting time of the Loran-C signals from the antennas relative to the common time reference. Thus the Loran-C signals combined with the RDSS satellite signals can become a new positioning platform. At the same time, an integrated receiver deals with the Loran-C signals as pseudo-satellite signals of the RDSS on the ground and determinates 3D position of the receiver and the difference of the receiver clock relative to the common time reference by use of four signals from RDSS satellites with Loran-C stations. It is the major source of positioning error that the Additional Secondary Factor (ASF) of Loran-C signal propagation over land path within this integrated system. The better way is making an ASF correction table over the coverage of Loran-C signals in China. A numerical integral equation mothed for calculating the propagation delay & field strength of Loran-C groundwave signal has been employed for ASFcorrection with a Geographical Information System (GIS) software included the geoinformation of longitude, latitude, altitude, ground electronic parameter, atmospheric refractive index. In October 2004 & July 2005, actual ASF measurement over an area around the Huangshan mountain was carried out. The theoretical predicted ASF by the GIS software & the traditionary Millington method have been compared with the actual measured ASF.The result shows the errors of predicting ASF reduce to about 0.5 microsecond.
Published in:	Proceedings of the 2007 National Technical Meeting of The Institute of Navigation January 22 - 24, 2007 The Catamaran Resort Hotel San Diego, CA
Pages:	357 - 360
Cite this article:	Chen, Hongqing, Chen, Xiuming, "ASF Correction Within an Integrated Navigation System of Loran-C / RDSS," Proceedings of the 2007 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2007, pp. 357-360.
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