Worldwide Radionavigation Systems

The accuracy andor performance of navigation techniques has improved steadily since the early days of the cross staff and star sightings, and the current set of worldwide radionavigation systems has continued that trends. Loran-C, which became operational about 1960, has a location accuracy of 0.1-0. 25 nautical miles nmi, but its range is limited to 1,000-2,000 nmi. Omega, which became operational about 1980, is less accurate 2-4 nmi but provides true worldwide coverage. Transit, the first satellite navigation system, became operational in 1964. It gives worldwide coverage with two-dimensional positioning accuracy of 25 meters m but is limited to a minimum interval between fixes of 30 minutes or more. GPS, which is now becoming fully operational, provides full-time worldwide coverage with three-dimensional accuracies of 25m position and 0.1 ms velocity. Based on its technical performances, GPS is clearly the system of choice. It can also be shown, however, that GPS is probably the most vulnerable to interference or jamming.