The lives of sea turtles consist of a continuous series of migrations. As hatchlings, the turtles swim from their natal beaches into the open sea, often taking refuge in circular current systems (gyres) that serve as moving, open-ocean nursery grounds. The juveniles of many populations subsequently take up residence in coastal feeding areas that are located hundreds or thousands of kilometres from the beaches on which the turtles hatched; some juveniles also migrate between summer and winter habitats. As adults, turtles periodically leave their feeding grounds and migrate to breeding and nesting regions, after which many return to their own specific feeding sites. The itinerant lifestyle characteristic of most sea turtle species is thus inextricably linked to an ability to orient and navigate accurately across large expanses of seemingly featureless ocean.

In some sea turtle populations, migratory performance reaches extremes. The total distances certain green turtles (Chelonia mydas) and loggerheads (Caretta caretta) traverse over the span of their lifetimes exceed tens of thousands of kilometres, several times the diameter of the turtle's home ocean basin. Adult migrations between feeding and nesting habitats can require continuous swimming for periods of several weeks. In addition, the paths of migrating turtles often lead almost straight across the open ocean and directly to the destination, leaving little doubt that turtles can navigate to distant target sites with remarkable efficiency.

Wing Commander Anderson has drawn attention to the fact that the distribution of the larger navigational errors is frequently observed to be non-gaussian in character. He raises the point whether this can be accounted for by the generation of such errors in succession, rather than simultaneously. The successive generation of navigation errors arises through the error incurred on a particular leg being distributed about a mean which is dependent on the error up to the end of the previous leg.

When planning the replacement of an existing shore-based radar advice chain, which may have admirably served the port area under consideration for the past fifteen or twenty years, a number of basic elements have to be reviewed. The review and the ensuing process of analysis should be steps towards the adoption of a basic philosophy for the eventual development of a replacement system; this is necessary to judge requirements in relation to the many possible solutions, ranging from a simple shore-based radar advice service to sophisticated vessel traffic management systems. Elements for consideration include:

(i) The area to be served, present and future.

(ii) The traffic pattern, present and future.

(iii) The technology available or under development.

(iv) The other operational and administrative services available to shipping.

(v) The quality of manning and manning scales.

(vi) The economics of the shipping industry.

(vii) The cost of the new system.

(viii) The distribution of this cost over shipping and the community in general.

(ix) Legal aspects.

Besides these factual considerations and their analysis we should develop a philosophy regarding the aims of the system, which could be an improvement in port operation efficiency, in traffic safety, or in vessel turn-around time. The realization of these aims will probably result in economic benefits both for the port and for shipping and these will have to be weighed when investigating the distribution of system cost over shipping and the community in general.

This note on the distribution pattern of some Omega observations is based on a study of the phase differences observed at the Faculty of Fisheries at Hokkaido University (41° 48·4′N., 140° 43·3′E.). The A—D pair was investigated continuously, at half-hourly intervals, from i February 1974 to 31 January 1976, the A—C and C—D pairs from 1 January 1975 t o 31 December 197J and the A—H and D—H pairs from 1 January 1976 to 31 December 1976.

One of the main motives for establishing the International Hydrographic Bureau (1921) was: ‘To bring about … the greatest possible uniformity in nautical charts and documents’.

1. INTRODUCTION. Interest in the use of video displays for nautical chart presentation has increased rapidly during the last two years. Eaton et al. at the Second International Hydrographic Technical Conference provided a list of ten different systems already in production. Oshima speaking at a Workshop on the subject in Canada, early in 1985, mentioned that some 4000 Japanese fishing boats and 150 merchant vessels now carry electronic charts of varying degrees of complexity.

The aim of the Duke of Edinburgh's lecture is to extend the horizons J. of navigational interest. I shall try to show how modern scientific methods are greatly increasing our understanding of how the oceans themselves work, and, at the same time, do all I can to maintain that this new knowledge is not just a matter of curiosity. If vigorously developed it will be of much practical use to seamen, and of great benefit to us all. The time is opportune. Scientifically inclined nations recently have been making organized all-round exploration of the human environment. As well as major Antarctic operations, and the rush to Space, there is growing realization that the oceans are coming within our grasp for major technical exploitation.

This paper is concerned with measures which may be used to reduce the effect of echoes from the sea surface and from rain (sea and rain clutter) on radar displays so that targets which give a reflected signal power greater than the reflected clutter power can be detected. It should be noted that a conventional PPI display is fully brightened by signals of amplitude about three times the level of the inherent noise background, so that once the clutter has exceeded this limit it will appear on the display as a fully bright patch in which signals can be lost, even though their amplitude at the receiver input may be many times greater than the amplitude of the clutter.

Everyone now knows that radar has not fulfilled expectations as a means of preventing collision at sea, and that, because of this, its legal status is merely that of an aid to navigation. Nevertheless, everyone seems to feel that such a good technical instrument should enable ships to proceed safely in fog without reducing speed, and the fact that the collisions per fog day have increased by about thirty times in the fifteen years since radar became operational, shows that many mariners are in fact relying on it for collision avoidance. During these fifteen years, many papers have been published pointing out the dangers and giving advice, but in spite of this, the number of vessels involved in collision every year seems to have settled down to a constant figure of about 1700, or 7 per cent of the world fleet.

The objective of this paper is to show that an underwater navigation system can be developed that is technically and economically feasible and of high reliability for long distance under-ice operation. Recent advances in underwater navigation for cruise, exploration and search and rescue operations are considered and applied to the current interest in Arctic waters, where mineral prospecting and oil transportation are potentially important.

The paper was read at a meeting of the Institute held in London on 27 February 1974 with F. A. Haworth in the Chair. Mr. Cestone is from the Naval Ships Systems Command of the United States Department of the Navy; Mr. St. George from the Charles Stark Draper Laboratory of the Massachusetts Institute of Technology.

In this note I wish to enter however belatedly into the discussion of error distributions in navigation (cf. Anderson and Anderson and Ellis). Not being a navigator my arguments will be purely statistical, but I hope that they will throw some light on the problem, which seems to be an important one.

Hampton and Mills have commented that large errors occur more frequently than is predicted by gaussian behaviour; and Anderson remarks that in practice the ‘skirts’ of the empirical distribution are commonly hitched high over the estimated gaussian tails. The conclusion drawn is that navigational errors follow a distribution closer to the two-sided negative exponential than to the normal though, instead of peaking to a sharp point at the centre, the empirical distributions seem to have rounded heads.

One method of controlling aircraft is to assign each a given track, the distance between successive tracks being sufficiently great to ensure that the collision risk is very low. Most approaches to the problem of stipulating what this spacing should be, assume that the possible divergences of an aircraft about its preassigned path follow a Gaussian distribution with a standard deviation obtained by considering all the usual sources of navigational error (e.g. compass error and fixing error) together with meteorological errors due to inaccuracies in forecasting.

In June 1955, Canadian Pacific Airlines inaugurated a regular scheduled service between Vancouver and Amsterdam via the polar route. The Company had a wealth of northern experience which was of immense operational value on the polar route. In addition to its overseas services, C.P.A. has operated regular flights for many years to far northern parts of Canada and some of the group of companies which amalgamated to form C.P.A. in 1942 had arctic experience dating from the days when commercial aviation was in its infancy. One aspect of navigational experience which has helped its navigators on many occasions has been the map reading talents of the former bush pilots who show an astonishing ability to locate themselves visually over country which is mostly water, and where one lake looks much like every other lake.

The title of this paper could possibly be misleading in that it suggests that we already have a solution for a problem which is still open or at least a conclusion from an investigation which is still under way.

Accordingly, we should define straight away, subject to subsequent elaboration, (a) what we mean by an ‘advanced terminal area’, (b) what in such a context could be envisaged in terms of advantages for the aviation community, namely both the airspace users and the air traffic authorities, and finally (c) what new tools, both in the air and on the ground, would be desirable or essential in order to achieve a given degree of progress.

This paper reviews the history and the evolution of international ship collision avoidance research. The direction which research should take in the Chinese People's Republic is discussed and the authors recognize that new ideas may be needed to take account of the conditions in their country.

Improved radar surveillance for air traffic control can be obtained by the integration of radar systems. Integration, however, might cause the delay of radar information, which would hamper the air traffic controllers in their work. To estimate the delay, a mathematical equation to assess the amount of radar information causing this delay has been deduced from the properties of the behaviour of air traffic. The mathematical equation has been tested using results obtained from operational secondary surveillance radar in the Netherlands.

In recent years, the most striking development in the philosophy of navigation has surely been the change in attitude towards errors. Ten years ago an error was regarded as something that just did not happen in the best navigational circles; today we accept it as the normal concomitant of observation, and we study to reduce it.

This change in philosophy is really nothing more than theory following in the footsteps of the practical man, for the practical man has always regarded a position plotted on a chart with a certain amount of healthy scepticism. It may therefore be of value to discuss the whole business of errors from the point of view of the practical man, avoiding complicated mathematics and dealing in demonstrations rather than in rigid proofs. Navigation has been described as the business of conducting a ship on its way across the sea or an aircraft on its way across the sky. The word conducting implies safety. Indeed, safety is the keyword in navigation.

It is expected that the number of military and civil aircraft operating supersonically all over the world may remain the same during the next decade. The problem of sonic boom, which has been by-passed for military aircraft through the assignment of specially allocated ranges for supersonic operation, is still with us and is likely to influence the operation of supersonic transport (SST) aircraft, the Concorde and the Tupolev 144. Concorde is still short of reaching the break-even point, despite the large traffic gain registered on the routes to North and South America. The problem is to get overland routes; the difficulties encountered by the UK in the discussions with India and Malaysia for the establishment of a London–Bahrain–Singapore route are well known.

Before presenting the effects of the sonic boom on the ecology it may be well to summarize the nature and the main features of this phenomenon.

(i) The N-wave signature. A complex body like an aircraft, moving in supersonic flight, generates a pattern of local shock waves which tend to coalesce in two main shock cones, the front (or bow) and tail, as the distance from the aircraft increases. A shock wave is a discontinuity surface for the thermodynamic characteristics of the fluid, the most important being the static pressure jump responsible for the N-shaped pressure signature characteristic of the sonic boom. Other parameters are of minor importance to the environment. A shock signature is denned by the following parameters:

This paper describes the infrastructure and concept of two multi-site reference station differential GPS (DGPS) options being offered to land and marine users by Racal Survey. The infrastructure of the Racal SkyFix system is briefly outlined followed by descriptions of Racal's internetting and network capabilities.

The two systems are compared including infrastructure, differential data management, user coverage, datalinks and positioning performance in various parts of the world. The paper describes the design of each of the systems and the tests undertaken to assess their functionality, before going on to compare their performances under a variety of conditions. Emphasis is placed on the technical issues associated with multi-reference station DGPS including error sources, weighting observations and monitoring of the data. The fundamental approach of the systems is shown to achieve high data integrity which is necessary to develop the systems to their next phase.

Having described the two options, examples of various combinations of reference stations are used to illustrate the potential of the system and to show the increased performance over ordinary, single-station DGPS. The conclusions summarize the paper's findings and make recommendations for the future development of the system. The object of the developments so far have been to improve the quality of real-time offshore DGPS positioning. The internetting and network options are providing real-time results to illustrate the benefits and, together with SkyFix, offer significant developments in the ability of DGPS to provide accurate and reliable positioning over vast areas of the world.

In various papers published recently in the Journal and elsewhere, examples have been given in which the theoretical normal or gaussian distribution of errors does not correspond closely with the distributions found in practice; in particular the frequency of large errors is commonly underestimated by the normal law of errors. This discrepancy is discussed by Anderson who suggests that an exponential distribution may give a more realistic estimate of the frequency of large errors. A closely associated problem is that of determining the frequency distribution of the largest values occurring in a number of samples taken from some parent population. This problem has been solved theoretically for an important class of distributions and it is the object of this article to draw attention to this work and to show how it can be simply applied to practical problems, albeit in a rough and ready manner, without going far into the statistical details with which the subject abounds.