Published online by Cambridge University Press: 18 January 2010
The accurate, continuous determination of position, heading and course at all times, under all normal operational conditions, would be very desirable. This ideal has not been achieved for flights or voyages of long duration, but the many developments of recent years begin to give some promise that it may be possible. For high altitude aircraft the continuous optical observation of celestial bodies offers an evident solution, and doppler systems can give continuous speed over ground. For ships, however, the attainment of such an ideal navigation system is difficult. The various shore-based radio navigation systems have made important contributions, as have the development of inertial techniques. In addition, automatic optical sextants have been developed which can be used in clear weather.