Published online by Cambridge University Press: 18 January 2010
This paper discusses some of the variations that occur in the Earth-ionosphere waveguide that can contribute to errors in the Omega lines of position that are used to obtain navigational fixes on a world-wide basis. Effects due to conductivity variations in the Earth's surface, night to day changes in the lower ionosphere, multi-mode propagation, and solar disturbances of the ionosphere are considered and attention is drawn to the use of the multiple frequencies transmitted in the Omega format to overcome some of these sources of error. The paper was presented at a Marine Navigation Symposium held in Sandefjord, Norway, on 24–26 September 1969 and is reproduced with the permission of the organizers. (Crown Copyright, reproduced with the permission of H.M. Stationery Office.)