The usefulness of radar plotting, as at present practised, may be considerably enhanced by the application of a doppler radar technique which gives instantaneous measurement of relative velocity components and quickens the whole plotting process. The range and bearing of the target are given by an ordinary radar PPI, from which the rate of change of bearing may also be determined. The doppler radar gives an immediate measurement of the radial component of relative velocity and the derivative of radial velocity: from these data the course and speed of the target may readily be determined, using an automatic computer if so desired. Possible errors in deducing the true aspect and speed are discussed and the mode of operation, and principal design parameters of suitable doppler radar are given.i. INTRODUCTION. Although the number of collisions at sea between vessels equipped with radar continues to be a matter of grave concern, there has been little real progress in recent years in the development of anti-collision techniques. Whilst it is certainly true that so-called 'radar assisted collisions' are due to misapplication of the information supplied by radar, rather than to any shortcoming in the actual radar performance, there is frequent lament that information concerning the aspect of a target is seldom readily apparent, and many mariners would place greater confidence in their radar sets if aspect information were always immediately available as part of the normal performance.Captain F. J. Wylie (this Journal, 10, ^6) has postulated three factors for the reduction of collision risk in clear weather:
The difficulties of determining latitude and longitude under adverse weather conditions, when neither the Sun nor stars can be sighted, are well-known, and the advantages of a non-visual system of position finding which could operate through clouds or fog are too obvious to require emphasis.A Radio Sextant, which detects and locks-on to 8 mm. radiation from the Sun, has already been made and tested in America with reputedly excellent results. An analysis of both the theoretical and the practical design factors is given in the present paper, together with the results of successful experiments made in Great Britain.
The basic principles of radio sextants are reviewed and their application is compared and contrasted with that of infra-red and visual wavelength sextants. For maximum versatility an automatic sextant should be able to operate both on radio wavelength and at one of the others. A complete automatic system requires not only a means of making automatic celestial observations but also a means of carrying the data forward—that is to say, as inertial reference. In the paper presented in Paris the development of inertial systems was briefly reviewed with particular reference to linear vibration gyrostats which lend themselves readily to light and compact systems where the highest accuracy is not required.It is suggested that future developments in automatic navigation may well see novel forms of inertial reference coupled to radio sextants of millimetre wavelengths.
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