Doppler navigation

This paper describes a self-contained radio navigation aid for aircraft which works by virtue of the Doppler principle. Ground speed and drift angle are determined by measuring the Doppler shifts that occur when signals transmitted from a moving aircraft are reflected back from the ground along two or more beams. Ground speed with an error of less than 0.2% and drift angle with an error of less than 0.2° can be obtained with suitable equipment. Drift angle is combined with heading from the aircraft compass to give direction of travel with respect to north, and this information together with ground speed is fed to a unit which computes the aircraft´s present position. In general it is found that the accuracy of the indicated position is limited by the accuracy of the aircraft compass. Descriptions are given of the various units of the system, including an aerial which simplifies the problem of obtaining adequate accuracy. The errors are analysed and experimental results are given of those that occur over sea. An account is given of the experimental equipment that was built and tested at the Royal Radar Establishment and which formed the basis of equipments now in production.