Differential OMEGA/VLF as a World-wide Navigation Aid in the 21st Century

A. Stratton

Abstract:	The paper first reviews the factors that determine the accuracy with which the phase of a VLF transmission (such as Omega) can be predicted at a location and hence the inherent accuracy as a radio navigation aid;particular attention is given to differential operation. Differential accuracy depends wholly on the local direction of propagation (azimuth) and local velocity. Recent work is summarized which measured both fixed and time varying deviations from the nominal azimuth,calculated from geodetic propagation,and from the normal reference velocity.The azimuth deviations are particularly large at night and are thus the cause of reported reduction in accuracy of differential Omega at night. By real-time measurement,correction can be applied,to realize the inherent accuracy of differential Omega, 100m (68% linear) or better. Application is then discussed on both local and global scales. The case for implementation is discussed under the headings; - the need for an alternative to GPS, - the relationship of Omega to other alternatives, - economics. To meet the stringent safety requirements of civil aviation,if GPS were the only global aid, it may be necessary to increase the GPS constellation by three.It is estimated that maintaining the existing 8 Omega stations in service,augmenting by two additional stations and introducing a world-wide differential monitoring service,would cost a fraction of the capital and maintenance costs of augmenting GPS. The Omega option should be evaluated before irreversible decisions are taken on the future of Omega.
Published in:	Proceedings of the 45th Annual Meeting of The Institute of Navigation (1989) June 27 - 29, 1989 Alexandria, VA
Pages:	87 - 95
Cite this article:	Stratton, A., "Differential OMEGA/VLF as a World-wide Navigation Aid in the 21st Century," Proceedings of the 45th Annual Meeting of The Institute of Navigation (1989), Alexandria, VA, June 1989, pp. 87-95.
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