Secondary surveillance radar is a combined radar and communication system, which provides aircraft position (range and azimuth) on the radar side and identity and height on the communication side. It is a main working tool in Air Traffic Control today and the information it produces is an ingredient in providing separation between aircraft in flight. This paper is concerned only with the reliability of the identity (Mode C) and the height (Mode A) data, and not with the radar position data as such. ‘Reliability’ is taken to mean ‘can the values reported by the SSR be relied upon?’ Consequently we are not concerned with cases where an interrogation elicits no response, but only with responses which are present but not correct. Furthermore, a ‘Mode C discrepancy’ is defined as a read-out that disagrees with the altimeter reading observed by the pilot, so that we are not concerned with altimeter errors, but only with the faithfulness (or otherwise) with which the SSR reproduces the altimeter reading. In cases where the Mode C read-out is obviously wrong, but no pilot's report is available, it is not always possible to distinguish between an altimeter error and a Mode C discrepancy.

Introducing the notion of a pseudoloxodrome, we generalise a single-heading navigation to conformally flat Riemannian manifolds, under the action of a perturbing vector field (wind, current) of arbitrary force. The findings are applied to time-optimal navigation with the use of the Euler–Lagrange equations. We refer to the Zermelo navigation problem admitting space and time dependence of both a perturbation and a ship's speed. The necessary conditions for single-heading time-optimal navigation are obtained and the pseudoloxodromes of minimum and maximum time are discussed. Furthermore, we describe winds which yield the pseudoloxodromic and loxodromic time extremals. Our research is also illustrated with the examples in dimension two emphasising the single-heading solutions among the time-optimal trajectories in the presence of some space-dependent winds.

In the title to this paper I have deliberately used the plural, for I do not think it possible that the compass was only invented in one country and knowledge of it transmitted from there to other parts of the world. It is much more likely that the possibilities of its use, not necessarily for purposes of marine navigation, were discovered in several parts of the world, that some who knew of it transmitted it to their neighbours, but that in some areas the original knowledge was lost again. Of course such inventions may have had forms very different from the compass as finally used.

The first definite European account of the compass is contained in the writings of Alexander Neckam (1157–1217), about A.D. 1187. In De Utensilibus he wrote: ‘Qui ergo munitam vult habere navem…habeat etiam acum jaculo suppositam; rotabitur enim et circumvolvetur acus, donec cuspis acus respiciat orientem sicque comprehendunt quo tendere debeant nautae cum cynosura latet in aeris turbatione.’ The translation of this which I accept is as follows: ‘Therefore he who wants to have a well-equipped ship…let him also have a needle placed under a dart; for the needle will rotate until the point of the needle looks towards the East, and thus sailors perceive in which direction they ought to go, when the Little Bear is hidden in disturbed weather’. It has been suggested that in this passage ‘donec cuspis jaculi respeciat’ was probably intended for ‘donee cuspis acus respiciat’.

The following discussion took place at an Ordinary Meeting of the Institute held at the Royal Geographical Society in London on 19 February 1960, with the President, Wing Commander E. W. Anderson, O.B.E., D.F.C, A.F.C, in the Chair. Dr. J. G. Porter is at the Royal Greenwich Observatory, Herstmonceux, Mr. D. J. Cashmore and Mr. T. McClymont are both with English Electric Aviation Limited.

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.

Although INMARSAT's founding charter includes provision for a space segment for radiodetermination, the organization has, to date, concentrated on the telecommunications aspects of its mission. However, a satellite radiodetermination (including radionavigation) services development programme has been under way for about two years, and includes both study and experimental activities. Early studies performed for INMARSAT on both passive and active radiodetermination provided a number of significant conclusions, including the rather obvious but important fact that all satellite radiodetermination concepts possess two common elements: the forward transmission (broadcast) of a relatively wideband timing/ranging signal, and the precise tracking in orbit of the satellites.

In this paper the ship is treated as an information handling and processing system with a variety of information sources, sinks and processing areas both internal and external. Information flows and is processed in a variety of patterns depending on a number of variables. These include the proximity of other ships, the shore or the sea bed, the state of the weather, whether it is day or night and whether the ship is at sea or in port.

The author wishes to thank the Science Research Council for help in funding this study and also many industries and organizations for their assistance.

At the end of a conference held in London in June 1957 to discuss the avoidance of collision at sea and in the air, it was recommended that the three sponsoring bodies (the British and French Institutes of Navigation and the Ausschuss für Funkortung) should set up a representative Working Group to study the desirability of amending the Collision Regulations to take into account the use of radar.

The Group, which was formed in January 1958, was composed of the following members, not all of whom were able to attend every meeting: Commander P. C. H. Clissold (School of Navigation, University of Southampton), Captain W. H. Coombs (Honourable Company of Master Mariners, Barrister at Law), Captain R. Dublineau (Compagnie Générale Transatlantique), Captain P. Dupuy (Compagnie des Chargeurs Réunis), Captain H. Giessler (Ausschuss für Funkortung), Captain H. D. Harries (Regierungedirektor beim Bundesminister für Verkehr), Vice-Admiral K. Hoffman (Bundesverkehrsministerium), Professor P. Hugon (Professor Général d'Hydrographic, Rear Admiral, Ret.), Captain E. H. Ketels (Verband Deutscher Radar), Captain Le Bihan (Compagnie des Messageries Maritimes), Captain G. Lohmnitz (Norddeutscher Lloyd, Bremen), Captain P. Marchand (Ocean Weather Ship Service), Dr. F. W. Marienfeld (Bundesverkehrsministerium), Captain D. G. Tait (Honourable Company of Master Mariners), President Dr. R. Vogler (Bundesoberseeamt, Hamburg), Captain F. J. Wylie, R.N. (Director, Radio Advisory Service), Captain C. J. Wynne-Edwards, R.N. (Director, Compass Department, Admiralty Compass Observatory). The members of the Group served only in a personal capacity.

Global Positioning Systems (GPS) are now in use in many applications, ranging from GIS to route guidance, automatic vehicle location (AVL), air, land, and marine navigation, and many other transportation and geographical based applications. In many applications, the GPS receiver is connected to some form of intelligent electronic system which receives the positional data from the GPS unit and then performs the required operation. When developing and testing GPS-based systems, one of the problems is that it is usually necessary to create GPS-compatible geographical data to simulate a GPS operation in real time. This paper provides the details of a Personal Computer (PC)-based GPS simulator system called GPSIM. The system receives user way-points and routes from Windows-based screen forms and then simulates a GPS operation in real time by generating most of the commonly used GPS sentences. The user-specified waypoints are divided into a number of small segments, each segment specifying a small distance in the direction of the original waypoint. The GPS sentence corresponding to the geographical coordinates of each segment is then sent out of the PC serial port. The system described is an invaluable testing tool for GPS-based system developers and also for people training to learn to use GPS-based products.

Det Norske Veritas is a Norwegian ship classification society with a large classified fleet registered in 94 countries. The paper printed below was presented by Mr Cuming at an Ordinary Meeting of the Institute held in London on 18 May 1983 with Dr J. F. Kemp in the Chair.

Risk analysis is a method of evaluating potential risks which has been used for the past ten years by Det Norske Veritas, in both the shipping and the offshore fields of operations. The method is based on the systematic identification of hazards, the estimation of probability of occurrence and the evaluation of consequences.

Judging from what is written in early Sailing Directions and navigation manuals it would appear that seamen of North-west Europe laid great store in their knowledge of the nature of the bottom in the seas in which they traded. And indeed, even at the present time, mariners are provided (although they may seldom use it) with fairly detailed information about the sea-bed, designedly to assist them in pilotage. A navigator may read, for example, that:

‘The bottom in the Western Approaches appears to consist, mainly of fine or coarse sand, a great deal of broken shell, occasional patches of pebble, gravel, small stones, and, now and then, mud. The sand is mostly white, but in numerous places yellow sand and also black specks are met with…. The greater proportion of yellow sand is found to lie southwards of 49°30′ N and the far larger portion of black specks northwards of that line. This peculiarity is so marked, especially between 9°40′ and 7°30′ W that the mariner running eastwards, and supposing his vessel to be to the southwards of this parallel, should certainly suspect his having been set northwards of his reckoning if the soundings disclose this mixture of black specks to any great extent and with any frequency.’

This article treats integration of navigation data from a variety of sensors in a submarine using extended Kalman filtering in order to improve the accuracy of position, velocity and heading estimates. The problem has been restricted to planar motion. The measurement system consists of an inertial navigation system, a gyro compass, a passive log, an active log and a satellite navigation system. These subsystems are briefly described and models for the measurement errors are given.

Four different extended Kalman filters have been tested by computer simulations. The simulations distinctly show that the passive subsystems alone are insufficient to improve the estimate of the position obtained from the inertial navigation system. A log measuring the velocity relative to the ground or a position determining system are needed. The improvement depends on the accuracy of the measuring instruments, the extent of time the instrument can be used and which filter is being used. The most complex filter, which contains fourteen states, eight to describe the motion of the submarine and six to describe the measurement system, including a model of the inertial navigation system, works very well.

This Anderson Memorial Lecture was given to the Boscombe Down branch of the Institute on 19 February 2004. In the lecture Pinky Grocott, a distinguished navigator and past President of the Institute, recounts the history of the formation of Ferry Command set up to ensure the safe and efficient delivery of aircraft from North America to the UK during World War II. He then provides personal insights into his role as a young first-tour RAF navigator employed in the Command and describes the contemporary navigation practice.

The three basic problems of navigation are determination of position, definition of direction, and steering the direction required. In polar regions, all these problems are affected either by the high latitude, or by the polar climate, or by both. In this paper the various problems which arise are reviewed, possible solutions are discussed, and it is indicated where further research and experiment might be desirable.

In a recent paper I endeavoured to give a statistical solution of the problem of the separation of aircraft tracks with safety. In it I assumed that the distribution of errors of navigation made by the aircraft was a normal gaussian one; but I added a proviso that the effects of blunders might modify the result. From enquiries of various navigators as to the frequency with which they considered they were likely to make blunders I gathered that with a good navigator an undetected blunder might occur on 1 per cent of occasions and further it seemed reasonable to assume that a blunder might be defined as an error greater than three times the standard error of normal navigation. These assumptions are of course quite arbitrary but they seemed to be suitable to give examples of the effect on track separation; this was done in an unpublished paper. In these examples it was supposed that aircraft flying in the same direction were using two parallel tracks distant L apart and on each track aircraft were flying at fixed intervals but quite independently of the aircraft on the other track.

This study aims to address the accuracy evaluation problem for rapid transfer alignment with the coexistence of large misalignment angles and uncertain observation noises. For the requirement of accuracy evaluation, complete information in terms of misalignment angles should be estimated during the alignment process. Thus, a fixed-interval smoothing approach is the core of solving this problem. In this paper, a new Divided Difference Filter (DDF)-based an Interacting Multiple Model Two-Filter Smoother (IMM-TFS) is developed to estimate the misalignment angles. The proposed DDF-based IMM-TFS releases the restriction of inverse nonlinearity by using the weighted statistical linearization regression method, and the resulting pseudo-linear model can be used for backward-time IMM filtering. The smoothing step takes into account the merging of estimations and the interaction of multiple models simultaneously. The new smoother is compared with the previous well-known methodologies in simulations. The results show that the DDF-based IMM-TFS can achieve better accuracy for misalignment angles estimation, and has a high efficiency for detecting the changes in a model.