The present paper reports a small part of a research project aimed at finding the cost of marine casualties. It is hoped first to find acceptable ways of estimating the cost of casualties and, by applying cost/benefit theory, to help decision makers to choose the most cost-effective programmes of marine safety and environmental protection.

This paper describes the historical background to the Göttingen Professor Tobias Mayer's bid under the terms of the Act 12 Queen Anne, cap. XX (1714) to obtain a reward for having constructed lunar tables of unprecedented accuracy (to about ± ½′) which promised to make both useful and practicable the lunar-distance method of finding longitude at sea. Parliament's decision in 1765 to award £3000 to Mayer's heirs marked the end of an eleven-year period of lively correspondence conducted on the latter's behalf between Professor Johann David Michaelis, Secretary of Hanoverian Affairs in Göttingen, and William Philip Best, one of George III's Privy Secretaries in London. The Nautical Almanac came into existence as a direct consequence of the success of these diplomatic negotiations.

This account of a recent simulator experiment at the City of London Polytechnic on encounter reaction times at sea will also be published as an internal National Maritime Institute report.

Two ships are said to have an encounter when they pass within a certain distance of one another, say half a mile. The encounter rate bears a relation to the collision rate in a given area of sea and consequently it is desirable to minimize the encounter rate. The effect of routing in sea areas with a high density of shipping has been to reduce the total number of encounters but to increase the number of overtakings. Thus the introduction of a routing scheme greatly increases the proportion of overtaking encounters in the main lanes. For example, the routing scheme in the Dover Strait (with I per cent of through rogues) has increased the proportion of potential overtaking encounters from 27 to 95 per cent.

This paper examines the frequency distributions of the ranges at which vessels take action to avoid collision. Published data from simulator exercises are employed. Both give-way and stand-on vessels are considered. Lognormal distributions fitted to the data are shown to be superior to those previously published. Underlying ‘causal’ models are developed which are capable of generating the observed distributions.

Spacecraft which are sent on deep space missions to the planets must be accurately navigated in order to achieve the correct flight path. Navigation analysts use precise measurements and large computational software systems to determine a spacecraft's position throughout the mission and compute the velocity corrections for its guidance through space. When the spacecraft is launched into deep space on its voyage, it is impossible to know with great precision where it is headed. Imperfections in both the launch vehicle's terminal velocity and the uncertainty in the knowledge of the parameters which will affect the spacecraft trajectory contribute to errors in the predictions of the total flight path. Continuous navigation of the spacecraft achieves an ever-evolving prediction of its orbit from the reduction of radiometric and astrometric observations of the craft. Control of the spacecraft is achieved by computing and signalling to the craft a series of propulsive, velocity correction commands, which manoeuvre the craft to its desired course.

1. INTRODUCTION. In his Presidential address last year J. E. D. Williams treated us to a most absorbing, largely philosophical review of the development of the science of navigation over the last five centuries. In discussing the profound and enduring influence of radio waves on air navigation over the last century he commended as of ‘transcending importance’ the ‘homing quality’ of the radio beam in which the accuracy increases as distance from the transmitter decreases. He illustrated this ‘homing quality’ with references to the radio range for en-route navigation and the instrument landing system (ILS) for guidance to the runway. But he went further and remarked ‘Automatic landings in regular airline service are an example of how a perceived potential of the homing quality of radio has drawn to navigation a whole range of diverse applied sciences including, in this case, information theory, the properties of semi-conductors and the theory of servomechanisms and control, among many others.’

This paper deals with an analytical method for establishing a separation minimum for air traffic control using a monopulse SSR (Secondary Surveillance Radar), namely the Long Range SSR (LSSR), of which coverage is extended to 250 n.m. The azimuth estimation accuracy of the monopulse SSR was significantly improved compared with that of conventional SSR.

As an index of a collision risk due to azimuth errors of the LSSR, the close approach probability (CAP) associated with the probability of overlap of aircraft in azimuth is used for evaluating the safety of the surveillance system. The CAPs for both the LSSR and the conventional SSR are estimated by modelling and comparing distributions of azimuth errors. The CAP for the LSSR is significantly smaller than that for the conventional one under 5 n.m. separation minimum.

Earlier papers, based on a computer model of European air traffic, deal with the probability of conflicts arising between pairs of aircraft operating under free-flight rules. This paper discusses the problems of resolving these conflicts. When a potential collision takes place in the neighbourhood of other intruding aircraft, these must be taken into account when choosing an escape manoeuvre. A suggestion is made that may ease the problem.

Global Navigation Satellite System (GNSS) attitude determination and positioning play an important role in many navigation applications. However, the two GNSS-based problems are usually treated separately. This ignores the constraint information of the GNSS antenna array and the accuracy is limited. To improve the performance of navigation, an integrated attitude and position determination method based on an affine constraint model is presented. In the first part, the GNSS array model and affine constrained attitude determination method are compared with the unconstrained methods. Then the integrated attitude and position determination method is presented. The performance of the proposed method is tested with a series of static data and dynamic experimental GNSS data. The results show that the proposed method can improve the success rate of ambiguity resolution to further improve the accuracy of attitude determination and relative positioning compared to the unconstrained methods.

Vision navigation using environmental features has been widely applied when satellite signals are not available. However, the matching performance of traditional environmental features such as keypoints degrades significantly in weakly textured areas, deteriorating navigation performance. Further, the user needs to evaluate and assure feature matching quality. In this paper, a new feature, named Line Segment Intersection Feature (LSIF), is proposed to solve the availability problem in weakly textured regions. Then a combined descriptor involving global structure and local gradient is designed for similarity comparison. To achieve reliable point-to-point matching, a coarse-to-fine matching algorithm is developed, which improves the performance of the point set matching algorithm. Finally, a framework of matching quality evaluation is proposed to assure matching performance. Through the comparison, it is demonstrated that the proposed new feature has superior overall performance especially on correctly matched numbers of keypoints and matching correctness. Also, using real image sets with weak texture, it is shown that the proposed LSIF can achieve improved navigation solutions with high continuity and accuracy.

For underwater vehicle navigation sensors, the output signal periods are different and time-varying. This would result in the decline of precision, and even wrong results. To deal with the problem, this paper puts forward a multi-sensor, adjustable-period integrated navigation method based on multi-stage signal trigger. This method considers the valid signals of a Doppler Velocity Log (DVL) as the trigger signals of a Dead-Reckoning (DR) navigation program. It also considers the valid signals of an acoustic positioning sensor as the trigger signals of the integrated navigation program. In this method, it can adjust the filtering period in real time. According to the time label of signals, this method actualises the time-space alignment of sensors. Then it conducts DR navigation and integrated navigation. The method can not only utilise the valid signals of each sensor sufficiently but also fuses the data based on time-space alignment efficiently. Sea trial data shows that when the output signal periods are certain, navigation precision of the method in this paper is better than a non-adjustable-period filtering method. Moreover, in poor conditions, it can also attain a high precision.

Aided Inertial Navigation Systems (INS) systems are commonly implemented in land vehicles for a variety of applications. Several methods have been reported in the literature for evaluating aided INS performance. Yet, the INS error-state-model dependency on time and trajectory implies that no closed-form solutions exist for such evaluation. In this paper, we derive analytical solutions to evaluate the fusion performance. We show that the derived analytical solutions manage to predict the error covariance behavior of the full aided INS error model. These solutions bring insight into the effect of the various parameters involved in the fusion of the INS and an aiding sensor.

This paper reports a diary study of rendezvousing as performed by university students. The study compares students' performance when meeting at familiar and unfamiliar rendezvous points. It reports various findings that help to set goals for the development of personal navigation and related services at appropriate levels. For example, when meeting at novel rendezvous points, students: (i) fail to meet as initially agreed more frequently; (ii) report more stress and lost opportunity as a result of rendezvousing problems; (iii) change plan during the rendezvous more often; (iv) communicate more about the rendezvous, particularly using text messaging; (v) attribute rendezvousing problems to lack of geographic and travel information more often, and to additional, spontaneous tasks such as ‘popping to the bank’ less often. Meetings at novel rendezvous points are also more likely to include acquaintances and strangers.

Global satellite navigation systems (GNSS) are nowadays used in many applications. GNSS receivers experience limitations in receiving weak signals in a degraded environment. Hence, tracking weak GNSS signals is a topic of interest to researchers in this field. Different methods have been proposed to address this issue, each of which has advantages and disadvantages. In this paper, a method based on the vector tracking method is proposed for weak signal tracking. This method has been developed based on a strong Kalman filter instead of the extended Kalman filter used in conventional vector tracking methods. In order to adjust important parameters of this filter, the fuzzy method is used. The results of tests performed with both simulated data and real data demonstrate that the proposed method performs better than previous ones in weak signal tracking.

This work quantitatively analyses vessel traffic service (VTS) communications in ports and suggests improvements for more efficient control of the service. For this purpose, analysis of VTS communications was performed on VHF channel 12 in Busan North Port, South Korea. This communications service follows the queue of M/G/1 (the arrivals have a Poisson distribution, the service time is characterized by a general distribution, and with a single server). The degree of congestion of the communication channel was shown as the utilisation rate of the queue, which was 67·7% at peak times and 29·6% at non-peak times. To reduce congestion in the communication channel, we propose to separate the peak time control channel, exclude passing reporting, and decrease the reporting time. With separation of the peak time control channel, the utilisation rate decreased by 41·1%. The utilisation rate decreased by 5·7% when passing reporting was omitted, and by 8·3% when reporting time was reduced by 60%. The results of this study can be used as basic policy data to improve VTS, including reinforcement of the VTS officer's role and adjustment of the control report contents.

The very high frequency data exchange system (VDES) is promising in promoting electronic navigation (E-navigation) and improving navigation safety. The multiple access control (MAC) protocol is crucial to the transmission performance of VDES. The self-organising time division multiple access (SOTDMA) protocol, as the only access mode given by current recommendations, leads to a high rate of transmission collisions in the traditional automatic identification system (AIS), especially with heavy traffic loads. This paper proposes a novel feedback based time division multiple access (FBTDMA) protocol to address the problems caused by SOTDMA, such that collision of transmissions can be avoided in information transmission among vessels. Simulation results demonstrate that the proposed FBTDMA outperforms the traditional SOTDMA in terms of channel utilisation and throughput, and significantly reduces the transmission collision rate. The study is expected to provide insights into VDES standardisation and E-navigation modernisation.

The 11-year solar sunspot cycle is approaching a maximum in 2000. The sunspot activity causes an increase in the solar flux, charged particles and electromagnetic rays emitted from the Sun. This solar flux affects the ionosphere, thus influencing the transmission of radio waves through the ionosphere. The GPS satellite navigation system is affected in that the transit time of the signals varies, introducing position errors. Also GPS equipment may experience degraded performance in tracking of the GPS satellites due to scintillations, rapidly varying amplitude and phase of the GPS signal. The equatorial and high latitude regions are most severely affected by this increased ionospheric activity. Experience has shown that, in equatorial regions, errors of 10–20 m may be introduced in Differential GPS services, even on distances down to a few hundred kilometres from the reference station. During the peak of the solar cycle, for the next 3–4 years, this situation will rather be the rule than the exception in the affected areas. Fugro has introduced an enhanced real-time DGPS service utilising dual frequency GPS called Starfix-Plus in selected areas. This service removes ionospheric delay errors by calculating the delay using dual frequency GPS receivers on the reference stations and the mobiles. The resulting accuracy is down to a few metres, even using reference stations up to 2000 km away. This increases the availability and redundancy of usable reference stations in a region, increasing the probability that the required accuracy is available, even if individual stations are not available due to scintillations or for other reasons.

In the early sixteenth century, Portuguese navigators on voyages outside the tropics ran into an unexpected problem in navigating with the plane chart since the latter took no account of the convergence of the meridians. Voyages between Brazil and the Cape of Good Hope were accomplished much faster than the chart led them to forsee. To overcome this problem, were Portuguese pilots of the first half of the sixteenth century using globes to set their courses with on great circle courses? The general opinion is that they were not. Yet the mathematician Pedro Nunes (1502–78) describes in a short treatise entitled Tratado que ho Doutor Pedro Nunez fez sobre certas duvidas na navigação (published in 1537, but probably written in 1534) how the navigator Martim Afonso de Sousa, on his return from the east coast of Brazil in 1530–2, had asked him to solve several problems of navigation encountered on the voyage.

When a surface is mapped onto a plane so that the image of a geodesic arc is a straight line on the plane then the mapping is known as a geodesic mapping. It is only possible to perform a geodesic mapping of a surface onto a plane when the surface has constant normal curvature. The normal curvature of a sphere of radius r at all points on the surface is I/r hence it is possible to map the surface of a sphere onto a plane using a geodesic mapping. The geodesic mapping of the surface of a sphere onto a plane is achieved by a gnomonic projection which is the projection of the surface of the sphere from its centre onto a tangent plane. There is no geodesic mapping of the ellipsoid of revolution or the spheroid onto a plane because the ellipsoid of revolution or the spheroid are not surfaces whose curvature is constant at all points. We can, however, still construct a projection of the surface of the ellipsoid from the centre of the body onto a tangent plane and we call this projection a gnomonic projection also.