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.

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.

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.

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 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.

This paper commences by outlining the developments expected in en-route navigation capabilities in Western Europe and describes the current provision of surveillance employing monopulse SSRS. Following a brief review of GPS characteristics, it then considers the use of ADS, in conjunction with GPS, as an alternative and/or supplement to these ground-based systems. In the light of a simple cost comparison, it suggests that the space-based system could be very advantageous, particularly where new routes are to be established in areas with little or no ATS infrastructure. A final section discusses the possibility of using GPS for height-monitoring purposes as will be necessary when a reduced vertical separation minimum of iooo ft, is employed above FL290 in Europe, and elsewhere.

Recently, there has been wide-spread interest in the use of the Global Positioning System (GPS) for precision approaches in a civil aviation environment. However, most of the work to date in Europe and North America has treated a GPS/inertial reference system (IRS) combination as the source of guidance for this phase of flight. Since the US has a very large general aviation population, the FAA is very interested in determining the role of a stand-alone implementation of differential GPS (DGPS) as a navigation sensor for precision approaches. This paper has two parts: a summary of the analysis of this application of DGPS; and a discussion of the navigation satellite test bed that is under development at the FAA's Technical Center.

The first part contains proposed accuracy, integrity and availability operational requirements, and their air traffic implications. A stand-alone DGPS concept is developed, and analysed. The major results of the analysis indicate that stand-alone DGPS may not fully meet Category I (CAT I) accuracy requirements. The results of the analysis are then used to provide the rationale for the major recommendation: that FAA pursue an implementation of a wide-area DGPS (WADGPS) to achieve a Near CAT I precision approach capability. The second part of the paper discusses the three-phase navigation satellite experimental programme that is being developed to acquire the data to validate the enhancements to GPS, including a GPS Integrity Channel (GIC) and WADGPS. The objectives of each of the experimental phases are presented and discussed. Then the experiments of Phase I that address GIC/WADGPS are discussed.

Over 20 years ago, collision with high ground was identified as being the single most significant cause of fatalities among air travellers worldwide (Smith, 1968), and some human factors responsible were highlighted. The three factors most commonly found to be present during major civil aviation accidents were: (i) pilot's visual flight in instrument meterological conditions (IMC); (ii) navigational error by the crew and'; (iii) pilot's failure to react correctly to new circumstances resulting from air traffic control (ATC) instructions or advice – sometimes made in a language foreign to that of the aircrew. The latter factor will be tested here to see if it still applies to recent cases in the UK.

This paper, and the following two papers, were presented at a joint meeting sponsored by the Institute in association with the Honourable Company of Master Mariners and the London Branch of the Nautical Institute. The meeting was held at Trinity House on 20 November 1991. This first paper was read by Captain Houghton.

The weather is rarely out of the news. Weather can be hazardous at times almost anywhere on Earth, and the media are always keen to report dramatic events. On the global scene, weather, climate and the environment are issues of great international public concern at present because of the likely implications of increases of greenhouse gases in the atmosphere. The contributions of the meteorologist to the understanding of this global problem are increasingly recognized, as is the progress which has been made in the accuracy of day-to-day forecasts. This paper provides a brief résumé of our present ability to model and forecast the behaviour of the global atmosphere and the ocean surface, and also demonstrates how these models are applied to the practical problems of operational ship-routeing by the UK Meteorological Office. It is worth remembering that it was the very high incidence of losses at sea in the 1850s which brought about the establishment of the UK's first meteorological service.

British Airways was recently granted permission for its fleet of Boeing 747-400 and 767 aircraft to operate using automatic landing systems in Category IIIB conditions; that is, decision height lower than 50 ft and a runway visual range of less than 200 m. This development might lead some people to think that the weather is no longer a significant factor in aviation operations. However, while these developments are taking place one sees reports such as ‘departure delays are still on the increase’; ‘poor weather slowed airport operations’; ‘BA flight from Singapore delayed by strong winds was five minutes from declaring an emergency’; ‘heavy rain might reduce wing lift when an airliner most needs it’. These reports confirm the realistic state of affairs that the weather, despite the introduction of modern avionics on board the aircraft, and automated instrumentation on the ground assisting aerodrome operations, is still a vital part of aircraft operations decision-making, affecting the safety and efficiency of flying.

A research and development programme performed in Sweden over a period of 9 years has created a substantial know-how on the design of satellite navigation user systems. Thus, a basic user system, called the GP & c Total System has been developed and tested over 3 years. This system can serve as a basis for the tailoring of an almost endless number of applications. The system is currently using data from the GPS satellites, but can also be operated with combined GPS/GLONASS receivers. The Swedish GP & c System is an example of how the communication, navigation and surveillance (CNS) concept and the various elements (ADS, ATM, etc.) for a new global Air Navigation System published by the ICAO FANS Committee can be implemented and integrated into a user-friendly operational system. The ICAO 10th Air Navigation Conference (5–20 September 1991) endorsed the FANS concept in which the main elements are based on the implementation of satellite navigation technology.

Columbus's first voyage to America has been widely regarded as a considerable feat of navigation. Feat it certainly was, but the great advances in navigation during the fifteenth century were in fact made by the Portuguese, whose adaptation and development of Mediterranean methods to the more demanding requirements of the ocean made the European voyages of discovery possible. It was in Portugal too, probably during the years 1478–85, that Columbus acquired his knowledge of navigation. This paper, which was presented to a meeting at Brown University, USA on 26 September 1989, where the author was Gulbenkian Research Fellow at the John Carter Brown Library, examines navigational practice in the Mediterranean during the late middle ages and its subsequent development during the Great Age of Discovery.

In this paper, a quantitative study is made of the determination of the level of a vessel traffic management system (VTMS) in a port. Also established is a mathematical model, which conforms to the actual situation in Chinese ports and which takes account of the ideas contributed by experts in relevant fields. With the help of the model, the port needs for VTMS are evaluated in a comprehensive and objective way, the overall levels of VTMS are determined and their corresponding standards set. A computer simulation verification has proven the effectiveness of the model.

This article addresses the mathematical foundations of rhumblines or loxodrome curves. These curves are critical to navigation and small-scale charting by virtue of the fact that they provide an efficient routeing from one point on a surface to another by means of a constant ‘course angle‘. This article will develop the necessary mathematical relations for the construction of such a curve, then apply the relations to both spherical and oblate-spheroidal surfaces. The purpose of this article is to produce a superior oblate-spheroidal loxodrome curve, which better models curves or routes of constant course on the actual, approximately oblatespheroidal, Earth.