In 1965, following the Eastbourne Conference, the British, French and German Institutes of Navigation formed a Working Group to make a study of the environment in which the supersonic transport will operate and of its implications for the navigation of such aircraft. The Group's initial task has been one of education, largely through discussion of a series of papers submitted to it. Some of the papers considered have already been published in the Journal (Vol. 19) and a further selection is published below. Table I was contributed by Mr. G. E. Beck. The illustrations to these papers have not all been reproduced.

1. Atmospheric Conditions. It will be useful to distinguish between different kinds of atmospheric influences on supersonic aircraft operations. They may be classed as follows:

(a) Sporadic effects near the ground

(b) Sporadic effects in the free atmosphere

(c) Effects on sonic boom

(d) Effects of atmospheric ozone

(e) Permanently effective atmospheric parameters, such as temperature, density and wind.

In 1961 the Institutes of Navigation in Great Britain and France, with the Deutsche Gesellschaft für Ortung und Navigation, formed a representative Working Group to go into the question of regulating traffic in converging areas at sea with particular reference to the Dover Strait. The Group's Report, which was published in October 1962, made certain proposals for routing traffic in the area which were accepted, in April 1964, by the Maritime Safety Committee of the Inter-Governmental Maritime Consultative Organization.

The Loran C radio position-fixing system has been described in technical detail at international conferences and elsewhere. This paper tries to convey the general ‘feel’ of the system and its characteristics and to indicate, with as few irrelevancies as possible, what sort of process makes the two readout counters go round and give the navigator his position fix. The equipment to which the paper refers is the AN/SPN-31 marine Loran C receiver, which was designed and produced by Decca to a U.S. Bureau of Ships specification. Individual makes of Loran C set differ in various ways, but SPN-31 will serve for illustrative purposes.

1. Hovercraft Environment. With the exception of the sidewall craft which is unlikely to achieve speeds in excess of 30 knots, all hovercraft depend on their ability to rise clear and free from water drag in order to achieve their high economical speeds. Nevertheless a hovercraft will tend to conform with the surface over which it is travelling. A rough sea produces a rough ride which at speed produces a motion not unlike that of a car going over a series of hump bridges with vertical accelerations in the order of 1½ g—one needs to be strapped into a seat. The most efficient means of propulsion is achieved by using air screws; these are noisy and necessitate crew members using an intercom. Control surfaces, rudder and airscrews are aerodynamic and to reduce air drag the hovercraft is likely to be low in silhouette and give poor all-round vision to the command. The biggest single factor is drift; being aerodynamic and free of water drag, the hovercraft is completely wind borne and in moderate beam winds can track with as much as 45° of drift angle on and turns out of wind can be alarmingly large.

This paper contains a brief survey of a series of instruments which have been developed for use in sailing yachts. It then outlines the principles of two computers; one navigational, the other for sailing performance indication. It does not cover radio navigational aids, echo sounding or radar. The data requirements are: 1. Navigational, comprising distance run through the water, heading, leeway angle. 2. Functional, comprising speed through the water, direction of the apparent wind and speed of the apparent wind.

For measuring distance run, the classical towed rotator type of log, fitted with a mechanical or electro-mechanical revolution counter has been largely superseded in racing yachts by logs employing through-hull sensors on account of drag considerations and the inconvenience of having to shorten the line when sailing slowly in shallow water. It still finds favour in cruising yachts on account of its generally lower price and its simplicity.

Mr. Blake has given us an outline of what is needed in the context of Navigation of Long-Range Subsonic Transports in the 1970's. I now intend to pursue the theme by saying what I think v.l.f. navigation techniques can contribute to the solution of the navigation problem. In particular, I want to talk very briefly about the contributions that we feel v.l.f. might make towards the particular problem of limiting the numbers of aircraft which creep beyond Mr. Blake's navigation tolerance ‘fringe’ in addition to, possibly, by adding navigational information, increasing the effective M.T.B.F. of the total navigation system.

Clearly, addition of equipment cannot reduce M.T.B.F. in the narrow sense of the term—more equipment must have more faults—but if one interprets ‘fault’ as the incidence of a navigation error beyond the specified limit rather than narrowly as an electronic malfunction, I do think that v.l.f. navigation has its contribution to make to effective M.T.B.F.

Since the last Institute meeting on the Admiralty chart in 1967 the compilation office, formerly at Cricklewood, has been moved to a new building at Taunton, alongside our printing works established there in 1940. Thus, except for a small office in Whitehall, which keeps in touch with the ever changing defence scene, the whole of our organization is now concentrated at Taunton, from where every week between 30,000 and 40,000 Admiralty charts are despatched, through our agents, to navigators in every part of the world.

As readers of the Institute's Journal will know, to mark the 21st anniversary of the Institute a special edition, entitled The Navigation Explosion was published. Papers published in this edition highlight the very rapid advances which have been made during those 21 years as a result of a happy marriage between the ancient art of navigation and modern science and technology.

The basic concept of case and cluster rotation in inertial navigation (IN) systems is introduced, and the reduction in the errors caused by changes in gyro and accelero-meter biases is illustrated. The general properties of cluster rotated systems are summarized and it is concluded that, although errors inside the Schuler loops may be drastically reduced by rotation, care must be taken to avoid error sources outside the loops.

Marine and air navigation can still learn from each other. Mariners are following aviation in adopting some routing and control but aviation could follow mariners in their refusal to accept routing and control unless it is cost effective. However it may be easier in the marine case to measure the cost and probability of a collision than it is in the aerial case. But many states have established mandatory airways and routes; originally their navigational aids were very useful and in the event of forced landing the search and rescue people knew where to look. But many airliners now have self-contained navaids like the inertial navigation system (INS) or doppler so that they can navigate off airways, and also forced landings are rare. In the history of air traffic control at first it applied only around airports; when it spread to routes many aircraft were quite happy to fly off airways. But now airways have proliferated and have become customary and respectable to airline pilots so that few complain when some states force aircraft to follow lengthy and costly routes. The only virtue of airways is their freedom, theoretically, from uncontrolled traffic and from military dangers. If A.T.C. were confined to those situations where the risk of collision without A.T.C. would be worse than, say 1 in 10,000,000, flying would be a little more expeditious, but everyone feels secure within the system and insecure, guilty and uncomfortable outside it, so A.T.C. is used universally by airliners.

An increasing number of reference stations have been established, leading to a sharp increase in the workload of Double-Difference (DD) baseline solutions, which are not appropriate for the integrated processing of denser networks. Correlations among the ambiguities in DD models are complex, and it is difficult to get precise solutions. This paper improves the DD ambiguity resolution performance over a long baseline, using a modified strategy based on an Un-Differenced (UD) and Un-Combined (UC) model. The satellite clocks are estimated as parameters, which are properly constrained by real-time satellite clock products for improving the smoothness of ambiguities. We use data from the Earth Scope Plate Boundary Observatory to examine the presented method in Global Positioning System (GPS) networks. Our method obtained more obviously centralised distributions. The successful fixed rate was 96·4% for the DD baseline solution, and 98·4% for the UD method. The proposed strategy is appropriate for the distributed architecture of extensive systems and avoids a heavy computational burden.

Inland waterway transportation is one of the most important means to transport cargo in rivers and canals. To facilitate autonomous navigation for ships in inland waterways, this paper proposes a data-driven approach for predictions and control of underactuated ships with unknown dynamics, which integrates model predictive control (MPC) with an iterative learning control (ILC) scheme. In each iteration, kernel-based linear regressors are used to identify the relations between the evolution of ship states and control inputs based on the stored data from previous iterations and the collected data during operation, so as to build the system prediction model. The data are dynamically used to fix the prediction model over iterations, as well as to improve the controller performance until it converges. The proposed approach does not require prior knowledge regarding the hydrodynamic coefficients and ship parameters, but learns from the data instead. In addition, it exploits the advantages of MPC in handling constraints with minimised overall cost. Simulation results show that the controller could start from a nominal, linear data-driven ship model and then learn to reduce the path-following errors based on the data obtained over iterations.

In an earlier paper the present writer drew attention to the distinction between mixed and aggregated distributions. Incidentally, two minor mis-statements in that paper should be corrected. The first sentence in the last paragraph of section 2 (page 72) should read ‘As σ2/σ1 (=k say) tends to either zero or infinity, X/σ increases indefinitely; whilst for k nearer unity, X/σ is smaller’. Also the last line of the Appendix should not terminate with ‘X/σ = 3·724’ but with ‘X/σ→∞’.

Mixed distributions arise when for example an error occurs either from one distribution with probability p, or from another with probability 1–p, as in a set of position line errors due sometimes to one and sometimes to the other of a pair of observers of differing precision. An aggregate distribution occurs when the error consists of, say, two sub-errors, one from each of the two distributions; as when Captain Flint marks the chart and Long John subsequently reads it.

This paper examines a new interpretation for spatial mutual information based on the mutual information between an attribute value and a spatial random variable. This new interpretation permits the measurement of variations in spatial mutual information over the domain, not only answering the question of whether a spatial dependency exists and the strength of that dependency, but also allowing the identification of where such dependencies exist. Using simulated and real vessel reporting data, the properties of this new interpretation of spatial mutual information are explored. The utility of the technique in detecting spatial boundaries between regions of data having different statistical properties is examined. The technique is shown to successfully identify vessel traffic boundaries, crossing points between traffic lanes, and transitions between regions having differing vessel movement patterns.

Two practical measures might go a long way at the moment towards solving some of the questions raised by Captain F. J. Wylie in his paper (Vol. VI, p. 271) and discussed in the last number of the Journal (p. 202). The first is the provision of a suitable plotting device. It should not be too difficult to evolve a mechanism whereby a strip of transparent tracing material is passed across the face of the radar screen by means of two rollers (similar in operation to the echo-sounder paper passing over the plate in the modern sounding machine) in a direction parallel to the ship's course and at a speed representing that of the vessel and proportional to the scale of the radar picture in use. Plotting would be done by marking the ship's position and all other objects on the screen at short intervals and joining the consecutive positions of each object with a line. There would then be a continuous and up-to-date true plot of the area, which would be no more cluttered up with plotting than the actual area was with ships and objects.

Markley variables have advantages of slow variation, easy numerical integration and high precision in describing the attitude of spinning spacecraft. Previous attitude estimation methods based on Markley variables for spinning spacecraft usually employ a sun vector from the sun sensor, a magnetic vector from the magnetometer, or the angular rate from the gyro as the measurement. This paper proposes a Markley variables-based attitude estimation method using optical flow and a star vector from a star sensor as the measurement, where optical flow provides rate information and the star vector provides direction information. This method can estimate the direction of the spin axis and spin angular rate very well by using only one star sensor. In addition, the star sensor has higher accuracy than the traditional sun sensor and magnetometer, and the star sensor can also replace the gyro in case the gyro is out of action. The impact factors of this method are also analysed, which include spin angular rate, spin axis orientation and spacecraft moment of inertia tensor error.

This paper considers the need for better detectability of small targets at sea using marine radars in the 3 and 9 GHz bands. The problems of using radar reflectors and radar target enhancers to improve radar cross section, particularly when clutter is present, are discussed in detail. The IMO carriage requirement and the lack of suitably robust specifications are highlighted, and a proposal is made for a standard family of radar reflectors to meet the requirement. Radar target enhancers are also considered together with how these and radar reflectors should be mounted for best effect.

This article is based on a lecture to the Royal Institute of Navigation History of Air Navigation Group at Tangmere Museum on 12 May 2004. The author served as a navigator-radar – or a radar bomb aimer – within RAF Bomber Command during the mid-1960s. This article is based on his experience of this time in Bomber Command and describes how the Medium Bomber Force would have carried out their war operations had nuclear deterrence failed. In its day these plans were TOP SECRET.

This, and the following four papers, were first presented at the NAV99/ILA28 Conference on ‘Loran-C, Satellite and Integrated Systems for the 21st Century’ held at Church House, Westminster, London, 1st–3rd November 1999.

Just 25 years ago, the author presented a paper at the 30th Annual Meeting of the United States Institute of Navigation (ION) entitled ‘Radionavigation in North America, the Next 25 Years’. The paper received much attention and was given the ION's Burka Award for the best paper of the year. The author attempted to predict the worldwide implementation of Loran-C and Omega while acknowledging that satellite technology was on the horizon. ‘Global Radionavigation – The Next 50 Years and Beyond’ builds on the previous paper and is an attempt to define the future of global radionavigation based upon a mix of terrestrial and satellite systems. The time it takes for satellite systems and augmentations to mature and the reasons for this extended period provide the foundation of the paper. Also discussed are: the time to achieve a full constellation of space vehicles having signal specifications that meet the requirements for safety-of-life, the political complexities to achieve international harmonisation of service, and the use of a common worldwide protected frequency spectrum. The need for terrestrial complements is presented from the standpoint of supporting satellite systems and as a back-up in the event of loss of satellite services.

GNSS relative positioning technique is an important field of study, in which the standard ‘GNSS Baseline Model’ is often used. Differencing between observation equations is used to construct the mathematical model, since this method can eliminate some common errors in the GNSS signal measurements. The ‘Orthogonal Transformation’ method can also construct the GNSS Baseline Model. However, as is described by some scholars, this model may avoid some drawbacks of Double Differencing (DD) while maintaining all the advantages. For comparison purposes, this model is evaluated and the theoretical equivalence of both approaches is proved for the short baseline from two aspects: the Integer Ambiguity Resolution and the conditional least-squares baseline vector.

COMPASS or BeiDou is the new satellite navigation system under construction in China. In this paper, the standalone performance of COMPASS is compared to the Global Positioning System (GPS), including: Single Point Positioning (SPP), differential positioning (DGPS and Differential COMPASS) and single epoch ambiguity resolution and positioning. Based on the results, it was found that COMPASS SPP performance is clearly worse than that of GPS, due to larger broadcast orbit and satellite clock errors, especially the latter. Differential positioning performance of COMPASS and GPS are essentially similar, with GPS marginally better. COMPASS single epoch ambiguity resolution performance is obviously better than that of GPS due to more observed satellites and the single epoch positioning performance of COMPASS and GPS are similar.