However misleading statistics may be, they often make an interesting study and those of marine collisions are no exception. In Volume 13 of this Journal, page 430, some figures were given for collisions in fog with radar, which permitted the conclusion that, in North-west European waters in 1959, each day of fog produced 1·2 collisions. Up to and including 1959 this figure was not rising significantly.

Aircraft navigation using doppler and orbital information transmitted from a satellite is shown to be feasible, at least in a limited sense, using the least squares, differential correction method of computation. If sufficiently accurate velocity information can be provided, this approach could yield positions for long-range aircraft that are an order of magnitude more accurate than have been achieved with other world-wide, all-weather, all-altitude systems, such as doppler and inertial navigators.

The least squares, differential corrections solutions for both position and velocity do not converge for reasonable initial errors. Therefore, accurate aircraft velocity components, such as those provided by a doppler navigator, must be known. For one-knot velocity errors the position of a 500-knot aircraft can be determined to one-half nautical mile or better for latitudes up to 70 degrees. Several-knot velocity uncertainties result in position errors of a few nautical miles.

The position accuracies for supersonic aircraft are limited by the velocity accuracies achievable with the best doppler navigators. Computational methods that yield velocity as well as position, so that the satellite system would not have to depend so much on another navigation aid, would be most desirable.

During the first years of the last war the navigational problem was how to get to the target at all. In such conditions solutions to the navigation problem are priceless. Towards the end of the war it came to be accepted that, in transport operations at least, guidance to destination was almost a matter of course. Navigational performance ceased to be regarded as a question of success or failure and became a question of efficiency. This development in air transport we owed most of all to the radio compass.

As the volume of civil traffic grew, it rapidly became clear that the major limitation on navigational efficiency of air transportation was (and it still is) air traffic control. Although there has been considerable interest in the optimum trajectory particularly in connection with turbine aircraft, the development of refined operating techniques has been damped by restrictions on their application by A.T.C. The flat assertion by some would-be supersonic aircraft manufacturers that the supersonic (unlike the subsonic) jet will not take NO for an answer from A.T.C. once it is committed to a flight programme has recently been a most valuable stimulus.

The A.T.C. problem is well known. It is generally accepted that the capacity of an air space depends on the quality of navigational data, of the data link between aircraft and control centre and of the data correlation capabilities of the centre.

This paper, and the papers by Gérardin and Payne which follow, were presented at the meeting of the Deutsche Gesellschaft für Ortung und Navigation held in Dusseldorf 5–7 June 1962 and are printed with that body's kind permission. An account of the meeting was published in the last number of the Journal (16, 111).

The scientific engineering review of the U.S. Task Force on air traffic control, known as Project Beacon, was completed in the fall of 1961. In their report to the Administrator of the Federal Aviation Agency, the Task Force makes no claim for originality of most of the ideas and recommendations which were presented. Consequently, many of the problems resulting from the proposed plan of action have been previously discussed. However, the very positive and specific treatment of basic principles and the presentation of clear decisions produced considerable impact. The blurred picture created by less definitive approaches has been brought into better focus. The remaining problems are reduced in number, implementation efforts can be concentrated and the probability of success has been increased.

This paper (which was presented at a meeting of the Deutsche Gesellschaft für Ortung und Navigation held in Berlin in April 1963) describes the navigational techniques of manned space flight as they are at present conceived by the National Aeronautics and Space Administration in the United States. Although the paper is written in a more or less popular form, it should be of wide interest to navigators in showing the lines along which thought on this subject is developing, in one country at least.

For a long time, in countries where the tides show a large rise and fall in certain waters, thought has been devoted to the exploitation of the power brought into action by this phenomenon. Anyone interested in the problem will be familiar with the names of Passamaquoddy, Cobscook, Petit-Codiac, San José and Mezen bays, and the Severn, Abervrach and Ranee estuaries. All these stretches of water have been, as some still are, the subject of investigations carried to very different stages, with a view to building barrages to hold the water brought up by the tide, and plants to collect power from its return.

At the present time, radar is taking a more and more important part in air traffic control. That part is certainly going to develop even further in coming years, with the steady increase of traffic and the general use of jets on main airlines. Radar control has the advantage of presenting the controller with a clear picture of the position of each target, associated with an instantaneous view of the whole air situation. And, because radar information is renewed several times per minute, the situation displayed is always up-to-date. Unfortunately, that situation is rather anonymous. To make it usable, the targets observed have to be identified. In the first place, we have information about them from the flight plans; the identification of a particular aircraft then reduces to a choice between a few possible echoes only. A commonly used method is to send an order to the target to manoeuvre: the target obeying that order identifies itself by doing so. This method is simple, but not very quick. Moreover, the ordinary PPI unfortunately does not retain a memory of such an identification.

A radar installation, designed to serve as a navigational aid, is in course of being set up at the mouth of the Gironde. It is one of a long series of port- or river-radars installed in similar conditions. So far, these have been entrusted to port officials. They are used, almost exclusively in reduced visibility, to give ships accurate information about their position, and in particular to keep them informed of the presence of ships in their vicinity. Their chief function, in association with radio-telephony, is to allow traffic to be controlled at times when visual signals cannot be distinguished.

The Gironde enterprise is more ambitious. The intention is to entrust the radar to pilots so that they may guide shipping, in both clear weather and fog, without having to go on board. This method is to be used between the sea and Le Verdon, and in particular at the bar, the trickiest section of this stretch. It should entail a considerable reduction in the cost of pilotage, the chief of several reasons for this being that there would no longer be any need for a pilot-vessel. It is worth examining whether this is a sensible plan and under what conditions it can be made effective, in the Gironde or elsewhere.

That a pilot should use radar to direct a ship from some distance away is a completely revolutionary idea.

The following is an abbreviated version of the 29th Haldane Memorial Lecture given by Sir Frederick Brundrett in the University of London Senate House on 7 March 1963. Sir Frederick is Scientific Adviser to the Civil Service Commission.

If a radar transmitter and receiver are mounted together in the nose of an aircraft and flown at speed V over flat ground towards a vertical reflector (Fig. 1), then the received signal at the reflector differs in frequency from the transmitted signal by + V/λ (the doppler frequency), where λ is the wavelength of the transmitter. The reflected signal back to the aircraft undergoes a further increase of frequency + V/λ, thus the received signal at the aircraft differs from the transmitted frequency by + 2V/λ. This difference in frequency, referred to as the doppler shift, is proportional to the speed of the aircraft.

The continual increase in the complexity and performance of modern aircraft give rise to the need for improved accuracy and versatility in the electronic aids available to the crew. The system described is an example of digital computing techniques applied to the problems of air navigation. Navigation was chosen as a typical problem but the flexibility of the computer would allow it to be applied to other in-flight problems, such as the calculation of fuel and air data.

Dexan (Digital Experimental Airborne Navigator) is the outcome of some three years' work at the Applied Electronics Laboratories of the General Electric Company at Stanmore and the Royal Aircraft Establishment, Farnborough. The calculations performed by the computer to carry out a particular navigation process are shown schematically in Fig. 1.

It is now more than thirteen years since experimental work first started in Australia on controlled height/distance paths using radar distance and barometric height. At that time, however, the effectiveness of such a system was limited since no suitable altimeter with an electrical output existed, and since the number of radio beacons in existence was much smaller than at present. With the advent of more suitable altimeters, and now that distance measuring equipment (DME) is mandatory for all passenger carrying aircraft in Australia, work has been resumed and further trials have recently been carried out.

Aircrew reports of turbulence at heights between 20,000 and 40,000 ft. are analysed to show geographical and seasonal variation in incidence of turbulence. It is found that there is generally a summer minimum of turbulence and an autumn or winter maximum.

Reports of the occurrence or non-occurrence of turbulence have been made for the flights of Comet 4B aircraft of British European Airways. Although the assessment of the turbulence was no more than subjective it was thought that the uniform nature of the aircraft, operating over a large number of flight sectors in the European and Mediterranean areas, and the fact that ‘nil’ returns were also made, could give useful indications of the geographical and seasonal variation of the incidence of the high-level turbulence. An analysis of the reports, made during a period of twelve months, is presented here.

The following discussion took place at an Ordinary Meeting of the Institute held in London on 15 February 1963.

In 1518 a Spanish gentleman, just back from the West Indies, addressed a Summary of World Geography to his King. In the Dedication he pointed out that since the Pope's Line, which parted the Portuguese and Spanish spheres, ran through the mouth of the River Amazon, 28°W. of Ferro, all the World beyond 150°E. (i.e. 130°E. of Greenwich) lay open to exploitation by Spain. And according to the World Map of the day the area included Java, Japan, King Solomon's Ophir, and (best of all) the Spice Islands or Moluccas from which the Portuguese were already making fabulous fortunes. This gentleman was not the only person to speak to the young King on this matter. The captains and pilots who had opened up the Spice Islands for Portugal were dissatisfied with the rewards which their own King had given them, and a number of them offered their services and their special and secret knowledge to his rival. Ferdinand Magellan was one of them. From his experience in the Far East he was of the opinion that the Moluccas could be safely approached from the west, by way of the Great Ocean. And it should be emphasized that in suggesting this he had no romantic notions about becoming the first man to circumnavigate the globe. He put forward a business pro position which the Spanish King accepted. Immediately the most thorough preparations were set on foot. They included the making of new charts, new globes, new sea-quadrants and sea-astrolabes, by the best pilots and craftsmen of the day, of whom the most were Portuguese.

This paper is concerned with combining the information from a ground-based radio navigation aid (the Decca Navigator) with self-contained sources of dead-reckoning such as air data and doppler. The essentially complementary relationship between D.R. devices and a ground-reference radio system can be exploited so as to produce an airborne navigational system whose merit exceeds that of either component individually. There is, of course, nothing new in a proposition of this kind. It is suggested that a combination such as that of Decca and a self-contained dead-reckoning device can usefully be described as a ‘compound’ system since the whole is formed, to quote the relevant entry in Webster's dictionary, ‘by the aggregation of otherwise independent elements’.

Like Mr. R. S. Blicq (Journal 15,456) we have also been concerned in supplying details of the Sun's position to engineers on radar sites who use radiation from the Sun for, at present, two purposes:

(a) Measuring or checking the radiation pattern of the aerial in the vertical plane.

(b) Lining up the aerial in azimuth or elevation.

For these purposes the required accuracy of computation is usually about ±0°·1 in azimuth and elevation. Greater accuracy is never required, but less accuracy is sometimes adequate, up to ±1°.

We have found that graphical methods appeal most to engineers, and that even when a full table of values is supplied to them they prefer to display this information in graphical form. We have accordingly evolved a simple method of constructing graphs of elevation against time, and azimuth against time.

In order to achieve the required accuracy of ±0°·1 in elevation we have constructed a graticule of size 21 in. × 40 in. A skeleton version of this is shown in Fig. 1. The engineer has to know his latitude, and to find, from the Nautical Almanac or other source, the time of local noon (i.e. when the Sun is due south) and the mean declination, δ, of the Sun during the period of observation, which usually lasts up to three hours.

Each navigational aid has its advantages and disadvantages and for that reason the optimum aid will be a combination of several aids. The best way of combining the aids seems to be by means of an automatic dead reckoning computer which continuously computes position from true air-speed and wind-speed and other data which can be fed into the existing navigational aids by means of a data transformer. Data from the integrated system can be transmitted by data link to air traffic control to correct the flight programme, &c. This paper, which was presented at Dusseldorf at the German Navigation Society's meeting (5–7 June 1962), surveys the field of integrated navigation systems and describes a number of possibilities. Formulae are derived for the accuracy of Vortac and D.R. and Vortac and doppler. It is published with the kind permission of the German Navigation Society.

If we look critically at the navigational aids which are available today we find that all have advantages and disadvantages, and that no one aid can be claimed to be suitable for all purposes. This situation will still exist for many years. Therefore it seems very advantageous to combine the available navigational aids to form an integrated navigation system in such a way that the possibilities may be fully utilized.