The Navstar Global Positioning System (GPS) is a satellite-based passive radio-navigation system under development by the US Department of Defense (DOD) and due for operational deployment in the late 1980s. Each satellite carries an atomic frequency standard and transmits L-band spread-spectrum signals whose carrier frequencies and code epochs are synchronized with the satellite clocks. A suitably equipped user may measure the arrival time and frequency of the signals from at least four satellites to obtain accurate three-dimensional position and velocity information and, as a by-product, an accurate ‘system’ time.

This paper, which was presented at a seminar sponsored jointly by the Institute with the Nautical Institute in London on 9 December 1982, seeks to identify the environmental and political pressures behind the international and regional efforts to regulate the safety of shipping in European waters. It examines the role of Port State control and vessel traffic management in safety and the prevention of pollution.

The following Address, by the retiring Director of the Institute, was presented at the thirty-fifth Annual General Meeting held in London on 27 October 1982 at the Royal Geographical Society with the President, Captain B. J. Calvert, in the Chair. The President said that Mr Richey's pending departure (although he would continue to edit the Journal) was an event of considerable importance in the Institute's history and he felt it appropriate to have invited him on this occasion to present an Address in place of the Presidential Address normally delivered at the Annual General Meeting. Calling the Meeting to order, the President drew attention to a gavel, around which the names of past Presidents and Directors were to be inscribed, made from wood, for the anvil, from HMS Victory and, for the striker, from the yacht Jester. After the Address Wing Commander Anderson gave a reply reminding the Institute of Mr Richey's achievements during his long period in office. The audience then broke all traditions by giving the Director a standing ovation. His successor as Director, Rear Admiral R. M. Burgoyne, was then introduced to the Meeting.

Automated aids, computer assistance and other forms of advancing technology are gradually changing the human involvement in many tasks, so that the primary roles of man are to monitor, verify, manage resources and respond to emergencies, rather than to participate actively and continuously in the control loop. Many of the terms traditionally employed to designate or describe jobs are retained throughout this process although they are no longer apposite, and they can give a misleading impression of the nature of the residual human roles and of the skills required to fulfil them. In many respects an aircraft pilot may no longer actually fly his aircraft for much of the time, but monitor equipment that flies it automatically. A nominal supervisor may remain in many environments where revised human roles and facilities mean that effective supervision is impracticable. An assistant may not in fact be able to offer true assistance because he has no facilities to share any of the tasks, do parts of them, or assume temporary responsibility for them. The future navigator may not need to be able to navigate in the traditional sense.

It must be stated at the outset that the present author has a technical knowledge of Navstar GPS based only on fragments of the literature open to the public, and no knowledge whatever about the plans for its military use. An attempt will be made to discuss, from first principles, the consequences to both civil and friendly military users of the availability of a global, satellite-based navaid that makes possible the determination of position in three dimensions to a high accuracy. For civil users, confined to the ‘coarse acquisition’ mode, there is a 95 per cent probability that the horizontal position error will not exceed about 20 metres. For military users holding the key to a more sophisticated mode of operation, a significantly greater accuracy is available. The GPS also determines velocity, and data can be updated every second or so. It will be assumed that the navaid covers all the Earth's surface of interest, down to ground level. The cost of the satellite system is assumed to be high.

This paper describes the process of developing a safe access route to the Hook of Holland. The traffic situation in the Roads was tested by means of simulation. Van Riet, Pollen and Valstar are with the Directorate General of Shipping and Maritime Affairs in the Netherlands, Tresfon with the Maritime Research Institute in the Netherlands.

Since its inception in 1972 progress of the Channel Navigation Information Service (CNIS) has twice been described in the Journal. The tenth anniversary of the first broadcast bulletin of information occurred on 31 July 1982, and it is perhaps appropriate to review and bring up to date the major milestones in the history of the Service and to review the safety of navigation in the Dover Strait.

It will be recalled that, following the multiple collision off the Varne in 1971 and bearing in mind previous major disasters – Torrey Canyon, Pacific Glory, etc. – the Department of Trade concluded that a voluntary Traffic Separation Scheme (TSS), without surveillance and without a coordinating information service, was inadequate for the dense and complex maritime traffic problems of the Dover Strait. Thus was born the Dover Strait Information Service, now CNIS, under the aegis of HM Coastguard, and located on the upper floor of an old Port War Signal Station at Leathercote Point, St Margaret's Bay. The Decca Marine Radar Company installed a simple harbour radar and its associated display towards the end of 1971 and Coastguard evolved the essential elements of what remains to this day a half-hourly bulletin, broadcast on vhf/rt Channel 10. In low visibility intermediate broadcasts are given, based on actual visibilities reported from sea.

In August 1973 the French authorities installed a similar system at Cap Gris Nez and a very close co-ordination, vital from the mariner's point of view, developed.

Seafaring has always been an occupation which exposes the seafarer to more than an ordinary degree of risk, and a significant part of that risk arises from his inability always to know his position with sufficient accuracy as and when needed. This lack of precision has always had a fundamental impact on the practice of navigation, the development of navigational aids, the production of charts and so forth, and to a much greater degree than is, perhaps, generally realized. As we are now approaching the time when a global capacity to fix position on demand and to a high degree of accuracy is becoming available it seems sensible that we should go back to first principles before forming a view as to its likely impact on future navigational practice.

One of the major concerns in the operation of an air traffic system is the maintenance of adequate separation between aircraft. The assurance of an ‘acceptably low’ risk of collision is a crucial element in the system design. A number of factors need to be assessed in this process. What is the navigational performance of the aircraft in the system ? What are the possibilities for radar surveillance ? Are procedural arrangements together with position reporting a suitable mechanism? What difference would be made by collision avoidance or warning systems? Given that any combination of these or other factors has an implication on the minimum separation between aircraft, the level of safety ‘assured’ has to be balanced against the costs of the various alternatives which may present themselves.

In planning for change the implications of new operating practices or devices have to be assessed carefully. For most changes the process is one of evolution rather than revolution, although collision avoidance devices may have more of the latter's characteristics. Even for ‘revolutionary’ changes it may be possible to model the new system. Thus the existing situation is studied and its characteristics observed, then there are hypotheses of the ways in which the change alters the mechanisms in the system and finally the likely effects on system performance through mathematical and computer (often fast-time simulation) modelling.

Work on integrated navigation for aircraft started at RAF Farnborough at least as early as the mid 1950s. At that time the Inertial Navigator (IN) for a guided bomb was being developed and the navigation of the aircraft to the target used a combination of the weapon IN, Doppler radar and position fixing. An output of the navigation process was a calibration of the weapon IN. The operational concept was interesting in that after weapon release the aircraft had to return home using Doppler and compass.

Development of this system included flight trials in raf and a & aee aircraft using the Decca Navigator chains in Southern England for position reference. The same method was used in the development of the FSP 100 IN intended for the TSR 2 which took place in 1960/63. On these trials an early airborne digital computer on board the trials aircraft enabled Decca, Doppler and the IN information to be recorded and processed in-flight in a form suitable for post-flight analysis using a ground digital computer. This technique formed the basis for producing the reference navigation system which has been used for all our subsequent trials. The production of a position, velocity and attitude reference system for trials of inertial and other navigation systems has formed a major objective for RAE work on integrated navigation since that time.

The feasibility of utilizing psychometric tests to investigate accident liability at sea has previously been reported. Analyses of four psychometric tests and ship handling measures, using the statistical techniques of factor analysis and discriminant analysis, investigate the relationship between safety margins and accident liability and support and expand upon earlier conclusions. Evidence is also provided on the validity of a perception-of-risk test for navigators.

Over the last decade there has been considerable development of the applications of modern technology to the avionics of new aircraft. Examples of this have been the provision of area navigation and flight management systems, and now with the advent of cathode ray tube displays there is the opportunity to provide a greater range of information to the pilot in a more readily assimilable form than is at present possible. There have been similar developments in computer assistance to air traffic control (ATC) to aid the ground controller. There has, however, been a tendency for these and other parts of the operational system to be improved without fully evaluating their interaction with each other, especially the interaction between ATC and the flight deck. Unless this aspect is studied it is probable that the full capability of the system with its potential for improving the safety and economy of operation will not be fully realized.

The Civil Avionics Section of Operational Systems Division at RAE Bedford, in collaboration with UK avionics manufacturers and funded by the Department of Industry, has been concerned for a number of years with the development and integration of these systems in the flight deck of the future and with the way in which they can be used to develop, in conjunction with ATC, an improved system of air traffic management.

The history of aeronautics has been marked by a number of revolutionary breakthroughs influencing both designers and users. A major example is the advent of jet aircraft. In flight deck instrumentation the technical revolution has followed a steadier course, enabling a gradual evolution from the rudimentary instruments used on yesterday's aircraft to the sophisticated instruments used today.

In this respect, the information displayed has evolved both in quantity and quality. This has gradually led to new flight deck designs such as that used in the Airbus A 300. The impression of a gradual evolution in instrument technology is due to the fact that information is often displayed in the same manner as before, i.e. using dial indicators. Today, a new revolution is taking place in commercial aircraft flight decks: the use of digital systems displaying processed data on cathode ray tube (CRT) displays.

Preliminary Studies. The use of CRT in flight deck instrumentation has been under study for a number of years. Many aircraft are already fitted with CRT for specific applications such as weather radar information and computer-processed data (on display units linked with computers).

The present CRT breakthrough is tending to compete with or replace conventional instruments. This tendency started in 1968–70, giving rise to a number of preliminary studies, with military aviation quickly taking the lead. Studies were also carried out in commercial aviation, for example those of the Boeing SST programme which, as is commonly known, was later cancelled.

Based on a survey of its members in Europe and the Middle East, IATA expects that by 1985 almost half their aircraft will be equipped with Flight Management Systems (FMSs) incorporating 2-D, 3-D or 4-D navigational capabilities. The prime aim of this very significant investment is to increase airline operating efficiency, in particular through fuel saving. Flight Management Systems can perform a wide range of tasks, including flight planning and performance management, for which inputs of meteorological data are required. The more sophisticated systems can accept a number of wind and temperature inputs for the climb and descent profiles plus a wind input at each way-point of the cruise phase. Any estimate of flight progress and fuel requirements based on the use of the most economical aircraft speeds, whether made by the pilot or by an FMS, can only be as good as the knowledge of the wind-vector data pertinent to the flight. Whereas FMS-equipped aircraft in level cruise can often ‘update’ or correct the forecast data relating to the next flight leg, this is not feasible when major changes of altitude are necessary, e.g. during the descent phase. Accurate meteorological data are essential to ensure the optimum results from the FMS.

During the early 1970s, before the fuel crisis began, some thought was being given to the problem of handling the rapidly increasing number of aircraft movements in Europe.

This paper reviews the measures commonly used in experiments to evaluate collision avoidance systems. The use of Closest Point of Approach, Time to Closest Point of Approach, and Manoeuvre Magnitude was criticized particularly for multi-ship encounters. However, the data do suggest that two measures, Entropy and the use of experienced judges to give rank scores of performance, seem to be good measures even in multi-ship encounters. The use of a composite measure is not experimentally evaluated in this paper, but it is suggested that if one were used, it would have to be very complicated. Mr Cook is with the Department of Applied Psychology at UWIST, Dr Crawshaw in the Department of Psychology at the University of Hull.

An examination of accounts of sixteenth-century voyages shows that the estimations of latitude then arrived at by astronomical means were subject to widely varying error. The purpose of the present study has been to discover by practical experiments at sea, with replicas of instruments in use at the time, to what extent the size and irregularity of the errors can be attributed to the characteristics of the instruments and to what extent they arise from other causes. Observations were made from a 9-ton yacht under conditions not wholly dissimilar to those obtaining in some of the very small ships whose voyages are recorded.

The evidence for latitude errors is derived from published studies and from the writer's own analyses of three voyages made in northern waters by ships of the Muscovy Company: those of Stephen Borough of 1556 and 1557 and that of Arthur Pet and Charles Jackman of 1580. These were chosen because the masters in that Company's service received the best nagivational advice of the time3 and from the early 1550s onwards regularly recorded both latitude and compass variation. Furthermore, the relatively low altitude of the Sun in the higher latitudes was conducive to greater accuracy with a cross-staff.

The traditional non-adaptive Kalman filter includes models of the error characteristics of the navigation aids in use and such filters are very successful, so long as their model assumptions approximate to the true error characteristics sufficiently closely. However, for any filter there will be times when the environment changes and one or several aids will have errors which are not consistent with the assumed error models. It is necessary to consider carefully the sensitivity of the filter to such changes and, where a significant reduction in performance ensues, modifications to the filter are necessary.

This paper introduces a Kalman filter which monitors the behaviour of internal variables to detect and characterize any model imperfections. The filter will then adapt its internal model of the environment accordingly. The discussion is restricted to the development of a navigation filter for integrating dead reckoning (EM log and gyrocompass) and Omega data. The principles are the same for any filter and details regarding similar analysis involving the use of other aids, for example Satnav and Decca, have been developed in a similar way.

Before implementing any filter it is necessary to understand the behaviour of the measurement errors. For the dead reckoning and Omega aids this behaviour is described in section 2, while section 3 outlines a filter for integrating these aids and introduces the problems of model imperfections.

In spite of, or perhaps because of, the almost universal use of some ftym of electronic calculator for the reduction of astronomical sights, there is a growing demand for a simple back-up method for emergency use when a calculator is not available. Presumably the need arises because of the disinclination to carry the material for a standard method in order to provide cover for the small chance of calculator failure. It is a surprising development, enhancing the continued interest in, and use of, astronomical navigation in a field increasingly dominated by instant and continuous position-fixing systems of high precision and universal applicability.

Similar considerations may apply to the ephemeris data, which are being increasingly generated by calculator or computer. However, to a precision adequate for emergency use, near-permanent data for the Sun and stars can be given in a few pages in tables similar to those for G.H. A. Aries (Vol. I) and the Sun (Vols. 2 and 3) in Table 4 of AP 3270 Sight Reduction Tablesfor Air Navigation. In fact the simplest conceptual solution might well be to carry the appropriate latitude pages extracted from the loose-leaf US edition, HO 249.

In 1948 I had occasion to review the existing tables for the reduction of astronomical sights (this Journal, Vol. 1, p. 298, 1948); the review was limited to intercept methods and, mainly, to those based on the use of the DR position.

The paper, an edited and shortened version of the original, discusses a new approach to the display of collision threat parameter areas, obtained as a result of theoretical considerations. It can be applied to radar-computer anti-collision systems as well as manual radar plots.

With the development of digital techniques, and electronic digital computers in particular, radar-computer anti-collision systems are now aboard ships. Digital processing of signals and data in such systems can be divided into three stages as follows:

(a) Primary processing, which includes an analysis of radar signals within one rotation of the radar antenna. A result of this processing would be the position coordinates of detected objects. For relatively simple algorithms and high speed of analysis, special devices are usually employed.

(b) A secondary processing, which includes a correlation of the information obtained in the primary processing stage; the objects' position coordinates in consecutive antenna rotations; and an estimate of position, motion and approach parameters. For secondary processing devices general-purpose mini- and microcomputers are usually applied.

(c) A graphical display of the calculation.

Estimation methods and filtering techniques are nowadays an integral part of any computer-based navigation system. The purpose of these techniques is to provide an estimate of required variables which is sufficiently accurate for real-time command and control purposes. Repeatability, which is important for so many applications, is deemed to be a by-product of the estimation process. For this requirement it is not strictly necessary for the process to be accurate, it is sufficient if it is only consistent; these are closely linked but one does not imply the other. The modern approach is to minimize the variance of the noisy observations or the sum of the squares of the residuals, and the methods available for doing this are increasingly refined. The impression given in the literature (and it is extensive) is that data processing can somehow compensate for the shortcomings of the basic sensors with respect to the operation being considered. Within certain limits this is true, but the real reason for the sudden surge of Kalman filtering for real-time on-line applications was the relative simplicity of the computational process. In a way, Kalman filtering has done for estimation theory what the Fast Fourier Transform has done for spectral analysis.

The concept is simple enough to state. It consists of combining two independent estimates of a variable to form a weighted mean. One of these estimates is a forecast and the other is the current measurement.