This paper is based on the Eva G. R. Taylor lecture given by the author at the Royal Geographical Society on 28 November 1990. The precise landfall of Columbus in the New World has been the subject of discussion for many years owing to various interpretations of the information given by copies of his log and his own statement that his San Salvador lay about 28° north. The twofold aims of the author's 1989 voyage were: first, to experiment with fifteenth-century methods and instruments to find out by practical experimentation how accurate the navigation at the time might have been and so cast light on this 4° error in latitude; and secondly, to follow the navigation information given by Columbus as closely as possible to assess the effect of the currents on his dead reckoning as clues as to his landfall.

As the title indicates, this paper is principally concerned with navigation as a profession, rather than the essential activity of finding the way there and back again that is continually practised by the whole of humankind. By a profession, I mean the acquisition of a set of defined skills through training and the exercising of those skills as a way of earning a living for most, if not all, of a working lifetime. And looking at the profession of navigation, two interesting facts emerge; one is that it is not a particularly old profession - a century and a half, maybe. The second is that it is not likely to get very much older, at least in the form we know it today.

This paper formed the 1992 Anderson Memorial Lecture. It was presented by Air Commodore Grocott at a meeting of the Solent Branch at the Warsash Campus of Southampton Institute of Higher Education on 12 March.

This is a synopsis of a paper that formed the 1991 Anderson Memorial Lecture. It was presented at a combined meeting of the Bristol Channel and Boscombe Down branches on 21 February 1991

Zheng He was the greatest navigator in China's history and he conducted major oceanic voyages, before the western ‘Age of Discovery’, at a time when the Portuguese under Prince Henry were just beginning to feel their way down the coast of Africa. Under the orders of Emperor Yongle and then Emperor Xuande in the Ming Dynasty, Zheng He led a fleet which was the greatest in the world in the fifteenth century and made, in all, seven expeditions to the Western Ocean from 1405 to 1433. His fleet sailed across most of the sea areas of the Western Pacific Ocean and the Indian Ocean, and visited more than thirty Asian and African countries and regions. This paper will mainly discuss the extraordinary achievements of Zheng He's expeditions and their navigational technology, and will also briefly evaluate their role in navigational history.

We describe a new type of radio navigation and tracking system which, unlike conventional systems, does not depend on a costly infrastructure of coherent radio transmitters. This new system measures positions using spatial, rather than temporal, coherence and can therefore use any existing radio transmitters set up for any purpose. We describe the principles of operation, applications and present results obtained with a demonstration unit (in Cambridge) which can measure the position of a motor vehicle to a precision of about 5 m using local medium-wave public broadcast transmitters.

This paper and the following five papers were presented at the NAV91 Conference on Satellite Navigation held at Church House, London, 6–8 November 1991. Copies of the conference proceedings are available from the Director, price £85 (non-members) and £65 (members).

In the last two years, the idea of a civil geostationary overlay (augmentation) to GPS and GLONASS has moved from the discussion/concept stage to something approaching reality. Many details of implementation have been or are in the process of being determined. Major developments that have taken place in this period of time include: (i) INMARSAT'S adoption of a four ocean region satellite deployment (three had been employed previously), now including one region (AOR-West) that covers the conterminous United States, (ii) Inclusion in the specifications, and contracting for, navigation repeater payloads in the four INMARSAT-3 spacecraft, now under construction, (iii) Major improvements in the Test Bed, bringing the test signals closer in function and structure to those to be provided through the INMARSAT-3 navigation payloads. (iv) Plans in the US and Europe to employ the Test Bed, or a facsimile thereof, for field trials of the GPS/GLONASS integrity channel (GIC) concept, (v) Endorsement of the ‘Wideband GIC’ concept (transmission at GPS L, frequency of a spread spectrum signal) by many members of the aviation community, (vi) Introduction and study of the possibility that the Gic might be able to carry some form of differential corrections in addition to the basic integrity and constellation augmentation functions. In other words, whereas two years ago we were still considering the possibility of a civil element of global satellite radionavigation, this year we are deeply in the process of putting the necessary elements into place.

In 1989 the International Maritime Organization (IMO) published its Provisional Performance Standards (PPS) for ECDIS (Electronic Chart Display and Information Systems) and asked member governments to assess these standards and submit their findings to the Sub-Committee on Safety of Navigation. IMO intends to finalize the standards in 1993.

The historical development of positioning in relation to the nautical chart is very briefly described. Present nautical charts are largely based on geodetic surveys which date from the 19th and early 20th century. This gave rise to the use of many local datums and there has been a need to provide the mariner with information to enable him to transfer his position from one chart to an adjacent one on a different datum. The sizes of discrepancies in position between various datums are given. The availability of the Global Positioning System (GPS) and the World Geodetic System 1984 (WGS 84) datum enables positioning on a single worldwide datum to become a reality. The important factors affecting the adoption of WGS 84 as the datum for nautical charts, namely data availability and the practical and political considerations, are discussed. The importance of the proper consideration of datum in relation to new developments in the use of nautical charts is also mentioned.

The principal characteristics of the GLONASS system, its current status and deployment outlook are considered. Comparison of the main characteristics of the GPS/GLONASS systems from the user's viewpoint is made. Proposals focused on the operations to be carried out to improve navigation determination accuracy for the users, provided with the combined equipment, are given. The data presented, received simultaneously on the user&s GLONASS equipment and a GP–500 GPS system, indicate that navigational determination accuracies of both systems are approximately equal. The key characteristics of 6–channel user facilities for civil aircraft and helicopters are presented. This equipment has been developed in the Institute of Space Device Engineering (ISDE) in accordance with a standard draft ARING on the combined system. The principal directions of the accuracy characteristic of the GLONASS system updating are considered. It is suggested to use the quantum–optical measurements on the Etalon satellite, launched into GLONASS satellite orbit, so that ephemeris information can be improved. The questions concerning supplying the system integrity and differential corrections information are discussed. It is proposed to combine the global system of integrity signal generation and transmission with differential corrections for regional systems. The version of the information frame developed in ISDE and intended for transmission of this information to users via geostationary satellites by means of signals similar to GPS/GLONASS, and without additional complication of user equipment, is presented here.

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.

Whilst unmanned aircraft (UMA) can be said to encompass missiles, targets for weapon training, preprogrammed reconnaissance drones and civilian systems such as radio-controlled models used to carry cameras, for the purpose of this paper we will restrict ourselves to aircraft which are capable of sustaining autonomous flight and accepting navigation commands whilst airborne. The terms applied to unmanned aircraft are variously UMA, remotely piloted vehicle (RPV), Drone and Unmanned Aerial Vehicle (UAV).

The proposal to develop an extensive North-West European Loran-C system, replacing many existing chains of the Decca Navigator System (DNS), has led to an intensive debate on the merits of the two navigation aids, especially in the United Kingdom. The paper reviews the principal sources of random and systematic position errors in the two systems. The wide range of DNS random errors, predominantly due to skywave interference, are compared with the Loran-C random errors, and typical coverage limits of acceptable repeatable accuracy are presented. The paper also identifies the factors which control the magnitudes of Loran-C and DNS systematic effects due to land paths. It demonstrates that differences between the two systems are substantially less than are predicted by simple models. Loran-C and DNS techniques for dealing with land paths are compared and the errors experienced by Loran users are shown to be reduced by modelling and publishing ASF values.

This paper is based on a presentation made by the author at a technical symposium of the Wild Goose Association.

This paper was presented at the SASMEX 92 Conference in London, April 7–9 1992. Permission to reproduce it is gratefully acknowledged.

The paper opens with a brief description of the formation and roles of the Civil GPS Service Interface Committee (CGSIC) and its various Sub-Committees, defining clearly the concept of civil GPS status and health information, and the information services which are necessary. The paper then concentrates on international implications, referring to the activities of the CGSIC's international Sub-Committee, the International Information Sub-Committee (IISC). The concepts of national points-of-contact and national information centres are introduced together with a description of their perceived functions, and this is followed by discussion of the products which they are expected to make available. The paper continues to describe the consequences that have been encountered by the IISC, and the action that has been or is being undertaken. The concept of so-called ‘active distribution’ is defined, and is followed by discussion of the dissemination not only of GPS status and health information, but of information about how that information can be obtained. The possibility of legal implications and the consequences is also discussed and developed towards the arguments for appropriate international agreements regarding the civil use of the Global Positioning System.

In planning routes between well-defined points of departure and arrival, both aircraft and ships can take into account forecast values of certain geophysical parameters so that the route chosen is in some sense optimized. For aircraft flying the North Atlantic, the methods used are described in the papers by Attwooll, Bennett, and Monk (all 1982). There have been a number of papers on ship-routeing; they were reviewed by Motte and Calvert (1988). It should be noted that whereas for aircraft the dominant consideration is the wind (for which the maritime equivalent is the current), ship-routeing on the trans-oceanic scale is dominated by considerations of waves. However, on smaller scales, currents can be the dominant consideration: for example, see the paper by Fales (1991). That paper does not make use of the basic theory that was applied to the aeronautical problem in the 1940s. Although the work reported here is orientated to aeronautical applications, it clearly has ramifications for certain maritime problems.

The collision avoidance of a pair of uniformly moving bodies is considered in three dimensions. The relative motion of the bodies yields an expression relating the time to closest approach, the minimum range, the current range and its rate of change, other variables being unobservable. A Boolean relation is then proposed that is satisfied whenever the minimum range and time to closest approach simultaneously fall below given thresholds. The relation is further studied, in particular with regard to the issue of false and premature alarms. An airborne collision avoidance system is a possible application.

In 1991 Trimble Navigation introduced a Global Positioning System (Gps)-based attitude determination receiver capable of 3-axis solutions with accuracy to several milliradians for airborne, sea and land platforms. This paper discusses the physical, architectural, and operational features of this receiver system. Analysis of system performance will also be reviewed for various configurations and user applications. The Trimble Navigation attitude determination receiver uses differential carrier phase techniques to determine azimuth, pitch and roll angles of a 3-antenna array. This product is designed to operate in a variety of user applications and to withstand rugged operating environments. Trimble Navigation has expanded its proven GPS sensor architecture to incorporate three independent RF sections and additional processing channels to measure and process the differential phase between antennas on two orthogonal baselines. Direct measurement of differential phase utilizing a common local oscillator provides highly accurate relative phase data. The navigation and attitude processor computes azimuth, pitch, and roll angles as well as position, velocity and time. The solution accuracy and stability statistics are sensitive to various parameters. Antenna baseline length, signal multipath, platform dynamics and filtering are investigated. Test data from static and various dynamic platforms are also presented.

1. Introduction. This paper is concerned with collision risk reduction through the identification, measurement and analysis of contributing factors and the evaluation of risk control measures appropriate to the approaches to the Strait of Juan de Fuca. Risk factors were identified through a traffic survey and collision probabilities were estimated and modified by a simulated modification to traffic routeing. Marine collision risk analyses have tended to describe the circumstances of collisions without comparison to the conditions encountered by marine traffic. In the absence of any test of significance, such an analysis is revealing yet provides an incomplete basis for traffic management decisions. This study examines the importance of contributing factors through such a comparison.

This paper, and the following one, were originally presented at an Institute afternoon meeting held at the RAF Museum, Hendon, on 5 June 1991. This first paper gives a personal view of the development and use of radionavigation techniques in the UK in World War II. The second paper gives some technical background to the systems discussed in the first one.