The shape, size and orientation of the protected volume of airspace generated by the airborne collision avoidance system currently known as TCAS II are derived. While based on constant-velocity aircraft flight paths the results are shown to have more general application. It is also shown how the essential features of the protected volume may be used to calculate alarm rates for some simple traffic patterns.

The United Kingdom's interest in the Joint Tactical Information Distribution System (JTIDS) and its Relative Navigation (relnav) capability began in 1979 with studies into an Electronic Counter-measures (ECM) Resistant Communications System (ERCS). The Singer Kearfott Division (SKD) Time Division Multiple Access (TDMA) JTIDS system, which includes a relnav and position reporting capability, was selected to fulfill this requirement. Early in 1985, approval was also granted to the Royal Navy to procure an ERCS.

Technical studies on JTIDS for airborne applications are being directed by RAE Farnborough and by ARE Portsdown for maritime use. Systems Designers Scientific (SD Scientific) is providing technical support in a number of areas including relnav.

This paper, which was presented at an Ordinary Meeting of the Institute held in London on 15 January, gives a very brief overview of JTIDS and describes the principles of relnav before outlining the structured approach to JTIDS relnav evaluation which has been adopted.

There can be little doubt that the overall standards of safety at sea are high, particularly with the traditional maritime nations. Cockcroft states that of a total of 22600 ships over 1000 g.r.t trading in 1979, 9400 were from the traditional maritime nations. He goes on to say that during the period 1977–9 these countries lost 16 ships out of a total of 189 worldwide losses. Thus the traditional maritime nations ran 41·59 per cent of the ships and incurred only 8·4 per cent of the losses. This does suggest that high standards are not universal and there may be considerable resentment among operators of high standard ships when casualties to sub-standard vessels result in the implementation of measures, such as marine traffic management systems, which give rise to increased operating costs.

There is an increasing interest in crossing situations. This has been stimulated by the success of traffic separation schemes to generally reduce the level of risk of collision from ships approaching in opposing directions. There have recently been crossing collisions in the Dover Strait which have occurred during conditions of poor visibility. These might have been avoided if the officers in charge of the vessels had allowed more time to manoeuvre. They bear witness to the fact that, in fog, a vessel can travel a considerable distance before its course alteration is detected on another ship's radar and appropriate collision-avoidance action taken by that other vessel.

For many practical purposes it is desirable to have a yard-stick with which safety can be measured. A criterion for the estimation of the safety of ships against collisions is outlined in this paper. The method is based on mathematical simulation and embodies all relevant factors. Numerical results are given for the English Channel and the German Bight showing the effect of parameter variations.

One aspect of marine navigation which has particular application to the protection of the environment is the establishment of traffic separation schemes and other routing measures in coastal waters. Extensive pollution may be caused by marine casualties. The use of routing to reduce the risk of strandings and of collisions between ships or with offshore structures will be considered in this paper.

The paper first of all defines conventional aids to navigation and compares both the historical and future roles of these aids in relation to developments in the field of radio navigation systems and technological advances in shipborne navigational aids. It goes on to emphasize the need to provide for all classes of vessel, i.e. those equipped with a high level of sophisticated shipborne aids and those equipped with a low level of such aids, including the not-so-well-found vessel, fishing vessels and leisure craft. Mention is made of present mandatory requirements in respect of the carriage of electronic shipborne navigational aids and the effect of changes in these requirements on the future role of conventional aids. The availability, reliability, accuracies and errors of both conventional aids and radionavigation systems are discussed. The paper concludes that, with the anticipated developments in the field of radionavigation systems such as Global Maritime Satellite Navigation, GPS, Differential GPS, Loran-C and Differential Loran-C, there may be a decline in the requirement for some conventional aids to navigation; the provision of these aids, however, is seen as still playing an important role in the overall mix of aids to navigation used by the mariner. The level of importance of this role bears a direct relationship to the level of shipborne navigational aids carried by the various classes of vessel and changes in the mandatory requirements for such aids.

Australia, with its large continental shelf, requires faster and more economic methods of conducting hydrographic survey. Backed by the Royal Australian Navy an experimental programme to investigate airborne laser methods was commenced in the mid 1970s and completed in 1984. This programme demonstrated that airborne laser depth sounding can be used effectively in Australian coastal waters. This paper reviews the achievements of the experimental programme and describes some features of LADS, a ‘Laser Airborne Depth Sounder’ planned for operational use by the RAN Hydrographic Service. The paper was presented at the Congress of the International Association of Institutes of Navigation, Tokyo, 1–5 October 1985.

In a previous paper the writer considered the problems of establishing latitude at sea in the sixteenth century and in part based his conclusions on the results of experiments made with modern replicas of the quadrant, the mariner's astrolabe and in particular the cross-staff, these being the instruments in use at the time. Reference was made to the backstaff or Davis quadrant which, though first described by John Davis in its simplest form in 1595 was not in effective use in its final version until well into the seventeenth century. It remained, together with the cross-staff, the principal altitude-measuring instrument in use at sea until the introduction of instruments of reflection in the eighteenth century and indeed continued in use long after that time, no doubt because it was cheaper than the new instruments, but perhaps also in part because of the ingrained conservatism of seafarers. The name ‘backstaff’ can be used generically to refer to all those instruments with which the observer turns his back on the Sun (e.g. the Gunter's bow), but they all post-dated and derived in concept from the Davis quadrant, which remained the most common in England and elsewhere. (The French knew it as le quartier anglais.) It is in this sense that the term is used here.

Positioning by navigation satellites is carried out in three-dimensional geocentric cartesian coordinates, X, Y, Z. This applies to both the Transit System, which has now been in operation for over 20 years, and the Global Positioning System which is being tested and is due to become operational in 1988. Traditionally, the cartographer, the seafaring navigator and the geodetic surveyor have always expressed their coordinates in geographical terms, i.e. latitude and longtitude, whereas the land-based civil engineer, surveyor and the foot (or mechanized) soldier preferred theirs in terms of projection grid coordinates, i.e. northings and eastings. Transformations between these various coordinate systems involve not only complex algebraical formulae, but also some very specific numerical parameters, which are appropriate for different countries and continents and which can only be determined empirically. Moreover, the treatment and interpretation of the different systems of coordinates may frequently involve some very basic conceptual misunderstandings. These include confusing astronomical latitudes and longitudes with their geodetic counterparts, treating projection northings and eastings as if they were ordinary plane coordinates and, in the case of positions derived from observations to Transit satellites, applying the wrong set of transformation parameters or using inappropriate geoidal contour maps. These are typical examples of the sort of common misconceptions leading to gross errors and affecting even the most precisely determined absolute positions. Relative positioning, with respect to another point or a framework of points with known coordinates, eliminates some of the worst effects of these systematic sources of error, and is commonly used in geodetic surveying. However, instantaneous navigation (especially by using satellites) is most likely to be based on continuously determined, successive absolute positions and will therefore inevitably be affected by reference system errors. This is particularly important in the case of land navigation where much higher accuracies will be expected. This is a review paper with definitions and descriptions of the various types of coordinate systems and their mutual relationships. Geographical and geodetic coordinates are discussed in section 2, and projection grid coordinates in section 3. This is followed, in section 5, by a description of three-dimensional cartesian coordinates used in conjunction with navigation satellites. A brief discussion on current and proposed navigation satellite systems is given in section 6 and the paper is concluded in section 7.

Magnetic sensors have been used in navigation for many centuries. During this time the effects of magnetic interference from ferromagnetic materials used in vehicle construction have become an increasing problem, and correction techniques have evolved progressively to allow the continued use of magnetic heading detection. The advent of the microprocessor has made it possible to take a fresh look at the problems of compass operation in vehicles and to devise more accurate processes for the correction of the indicated heading. The compass system described in this paper uses a mathematical representation of the magnetic environment based on fundamental physical principles to supply accurate heading information even in the most magnetically hostile land vehicles.

Large numbers of land vehicles, ranging from complex and expensive military vehicles to private cars, are fitted with, or are considering fitting, navigation systems from the range of systems available. Common requirements for all applications are that the navigation system should contribute to increased operational performance and, at the same time, reduce the crew's workload. A most important element of the system is the operator's display.