For centuries, celestial navigation was the main method of determining a ship's position at sea, especially when sailing into more exotic areas. Later on, vast areas of the oceans were only covered by the Omega system and there was still every opportunity of finding a position by using the sextant. Nowadays, with GPS coverage worldwide, we consider celestial navigation as an interesting back-up.

The 600-ton Norwegian sealer Norsel, commanded by Captain Guttorm Jakobsen, made the last of her annual relief trips to Queen Maud Land when she went south last December to bring home the Norwegian-British-Swedish Antarctic Expedition from Maudheim. During this trip the writer was attached to the expedition as naval observer. The ship remained at Maudheim for three weeks while an aerial survey was being carried out by the Swedish air unit which she had brought with her; during this time advantage was taken of fine weather and favourable ice conditions to make two survey trips along the barrier, one to the eastward and the other to westward from Norsel Bay where the ship was harboured.

The Panama Canal Company's Marine Traffic Control is being designed primarily to minimize ships' average transit-time and obtain optimum use of Canal facilities, but it also includes features contributing to collision prevention. It prepares an operation schedule consistent with the number and characteristics of ships that are in transit and with operating conditions. Actual operation is continuously monitored and signals currently displayed to pilots to facilitate close adherence to the schedule. If the contemplated schedule is cancelled, as by trouble in locks or sudden periods of poor visibility, re-scheduling is rapidly formed and signals transmitted to pilots in conformity with the new schedule.

The system's contribution to collision prevention includes elimination of several hazardous situations: (a) Undue crowding of traffic; (b) Lock-entrance stand-off delays due to untimely ship arrival, during which ship handling is difficult; (c) Meets or overtakes at potentially hazardous locations.

Further, when approaching a bend on which other ships would not be visible and at which the meet would be hazardous, a pilot is advised of the number of ships which will be round the bend before he reaches it. Also indicated is the number of meets due to occur immediately beyond the bend, a distance through which the manœuvrability of his ship would be affected by the manner in which he rounds the bend. The automatically operating system is based on transmission of data comprising ships' identities and locations to a central control point where the data is analysed by an electronic computer and from which advisory signals are automatically transmitted back to the ships.

For a circular contour, which is one of the methods for indicating an error boundary, the author has studied the conditions for the probability of a ship's position (fixed by two position lines) lying within a 95 per cent circle by probability integration. In this case, the coefficient in the equation to indicate the radius is a function of an intersecting angle and an accuracy ratio between two position lines. The author has examined several accuracy ratios and applied the system to the error boundary of a ship's position fixed by three equally accurate position lines. However, as interpolation involves both angle of cut and accuracy ratio, the process is somewhat troublesome.

In this paper it is shown that the accuracy contour for a fix is an ellipse, whether the accuracies of the position lines are the same or not, and a method is developed to replace an error ellipse for two position lines of unequal accuracy with an ellipse formed by two equal-accuracy position lines. The method is extended to three position lines of unequal accuracy. It then becomes possible to indicate an error boundary by a 95 per cent probability circle.

The Earth's magnetic field can evidently be divided into its horizontal and vertical components, the horizontal component being of more immediate interest to the navigator since it directs the compass needle in the horizontal plane. Whereas on the magnetic equator the full field is horizontal (about 0·400 c.g.s. units), in high latitudes, with the angle of dip between 60° and 70°, H, the horizontal force, maybe about 0·180 c.g.s. units. At the magnetic pole H is negligible and, given the opportunity, the compass needle would point vertically downwards, the instrument then having no directional properties in the horizontal plane.

Use of multi antenna GPS equipment for determination of a vessel's attitude holds some promise for the development of accurate and inexpensive attitude systems. An application for such systems might be to provide very accurate roll information for multibeam echo sounders.

The present state-of-the-art GPS attitude systems cannot meet the required accuracy and update rate for such applications. GEOTEAM A/S has therefore developed a PC-based system which combines GPS-based attitude with roll and pitch information from a Vertical Reference Unit (VRU) and heading from a gyro compass.

In such a combined system, the long-term high accuracy of a GPS-based attitude system is combined with the short-term accuracy and fast update rate of conventional VRUS and gyro compasses in order to achieve a resulting performance that is better than any of the systems. In effect, the GPS attitude is used to calibrate the VRU and the gyro compass in real time.

During the past year extensive tests have been performed with a system using a Trimble VECTOR II GPS attitude system with a 1 metre baseline between the antennas, both on a van (with an inertial navigation system as reference) and on a vessel. During November and December 1993 further tests were made with an Ashtech 3DF attitude system with longer baselines (7·5 m). These tests were made on a vessel where the combined GPS/VRU attitude was fed into a multibeam echo sounder. These tests were performed in cooperation with Simrad Subsea A/S, the multibeam echo sounder EM 1000 manufacturer.

Most lists of the seven wonders of the world include the Colossus of Rhodes. This bronze figure of Apollo, which the sculptor Chares took several years to construct, stood near a harbour on the island of Rhodes in the Eastern Mediterranean. It is reported that ships in full sail could pass between its legs whilst navigation lights were kept burning in its eyes. Whilst such descriptions are coloured by romance and myth, there is little doubt that early lighthouses were substantially tall towers supporting an open wood or coal fire. Such lights existed in Britain until as late as 1819, when Flathom light in the Bristol Channel was replaced by more modern equipment.

In time the open-flame coal brazier gave way to tallow candles. In 1696 Winstanley introduced a chandelier with tallow candles into the lantern of his famous Eddystone Tower. In 1759 Smeeton's Tower, which now stands on the Hoe at Plymouth, incorporated two superimposed iron rings that contained twenty-four candles.

By and large it was the improvements in optical systems that governed the development and introduction of oil and then, at a later date, electric illuminants.

The first attempt to intensify a lighthouse beam was in 1727 by the French at Cordouan. Mariners had complained that they could not see the light at more than 2 miles. In an attempt to improve on this, a cone of wood was covered with tin plate and suspended above the open fire.

The associate members of the North European LORAN-C System (NELS) will, before the end of the six-nation co-operation agreement in 2004, need to take a decision whether to prolong or decommission LORAN-C operation in Europe. The Minister of Fisheries in Norway has already indicated decommissioning of the Norwegian LORAN-C stations. Such a decision raises the fundamental debate about whether we can rely on GPS as a ‘sole-means’ system, or if we need a secondary backup system, such as LORAN-C. The purpose of this article is to highlight important aspects and conflicts related to an extension of LORAN-C in Europe. The focus will therefore be towards the limitations and vulnerability of GPS vs. the potential of LORAN-C improvements. The discussion will be based on a Norwegian nautical perspective.

To obtain accurate navigation results with respect to Earth simultaneously with those with respect to the target for an interplanetary probe to approach the target planet, this paper proposes a Radio/Optical integrated navigation method based on ephemeris correction, which deeply affects the fusion accuracy. In this paper, the model of the ephemeris error is established, and taking the analytical solution of the ephemeris uncertainty as measurement, the target ephemeris error and its covariance are estimated by Kalman filter and fed back to modify the force models. By correcting the target ephemeris and using information fusion, the Radio/Optical integrated navigation prevents the ephemeris uncertainty polluting the fusion accuracy, and efficiently combines the radio and optical navigation results. The results show the influence of the ephemeris error can be removed, and the Radio/Optical integrated navigation is capable of providing accurate navigation results with respect to Earth and the target. The results demonstrate the proposed method yields an accuracy superior to the conventional method, which proves its effectiveness.

The location of the wreck of Shackleton's ship the Steam Yacht Endurance is recorded in the expedition log books as 68°39′30′′S 52°26′30′′W. The methods and assumptions that went into obtaining this fix are examined in detail by consulting the original log entries with a view to understanding the size of the errors and uncertainties it may be subject to and providing guidance to possible future searches. It is found that a dearth of navigational sights around the time of the sinking, the inevitable growth of uncertainties in the chronometer time since rating and other factors, introduce the possibility of errors in the position of several nautical miles in both latitude and longitude.

Procedures based on solutions of the direct and inverse geodetic problems are presented and their application in orthodromic and loxodromic navigation is analysed. They can be used in traditional navigation during a route planning and during sailing on the planned route in real time. The optimal division of orthodromes during planning and locally predicted short loxodromes during sailing – which allow orthodromic navigation also in manual steering – are proposed.

It is, I believe, generally agreed that if the aspect of a ship could be seen on the radar screen from a range of 4 or 5 miles down, the information provided by the radar picture would be sufficient to prevent collisions from occurring. The aspect cannot be directly observed on an ordinary 3-cm. marine radar, but I think such a set could be modified in the following way to enable the aspect to be shown.

For a considerable time fishing vessels, merchant ships, long-range forecasters and oceanographers have needed up-to-date sea ice information. This paper describes how the heterogeneous mass of ice information combined with the very thorough climatic analysis now available has been used to produce for the first time an up-to-date picture of the entire distribution of ice in the Polar Basin and areas adjacent to the Atlantic Ocean.

For over a century a function of the Marine Division of the Meteorological Office has been the recording of Arctic and Antarctic sea ice, particularly since the Titanic disaster. However, the comprehensive hemispherical ice maps produced internationally have been several years in arrears. Ice information supplied to ships was therefore usually based on average conditions which suffice for planning well ahead or on long-range weather forecasts where it is necessary to follow ice development closely. It was decided in 1959 to organize a synoptic ice map with up-to-date ice and sea temperature information. Ice being more conservative than the weather, a map produced every ten days has proved to be sufficient.

A device has been developed to enhance the radar conspicuity of navigation buoys. It is also very effective on small craft. This paper describes the specification and testing of the device and discusses the regulatory position regarding its use.

For farming in the future, positional information is of particular importance. Out of a multitude of positioning systems, GPS/DGPS is the most suitable one. This system does not require any additional infrastructure and at the same time guarantees complete coverage of all tilled surfaces. The major application of positioning with GPS/DGPS is to be seen in the area of local information and documentation. By generating both planning and process data, it facilitates the operation and control of work processes (organic and mineral fertilization, plant protection). In the end, positioning leads to navigation, which, in the case of single vehicles and vehicle pools, will in turn provide completely new possibilities for development and application. For the first time, vehicles without drivers are conceivable. Thus, the completion of any kind of work on schedule, without time limitations, would become possible with the least possible stress for soil and environment.

The problem of the autonomous determination of the position of a moving object (inertial navigation) on the Earth is solved by gyros, accelerometers, integrators and a computer. We will indicate three possible schemes of inertial navigation.

The number of collisions and groundings and the contact damage suffered by merchant ships every year is considerable, the averages for the years 1965–70 inclusive showing that some 15 per cent of the world's shipping over 500 g.r.t. has been involved annually in such accidents. United Kingdom shipping is no exception, and collisions and groundings alone as reported in Lloyd's Daily Lists during the first four months of 1971 show that ships from some 27 companies were involved, some with more than one incident reported although none had more than three. Collisions, groundings and contact damage are likely to occur if a ship's captain and his bridge watch keeping officers do not have immediately available in a simple form, complete information about their ship and her navigational equipment, and detailed information covering the essential tasks performed on the bridge. Unfortunately however, in a great number of ships, most of this information is not provided in an easily usable form and, as a result, even the most competent of navigators is all too often unnecessarily placed in a difficult and sometimes dangerous situation.

Like any other vehicle a ship needs to be started, stopped and steered safely; the art of doing this is sometimes called ship handling. Successful ship handling depends upon three distinct operations: acquiring the right information, making the right decisions and performing the right manoeuvres. In this paper we assume that the Captain has all the facts and knows the right thing to do, and examine the physical ability of the ship as a mechanism to respond to his will.

In this paper, a simplified constellation architecture consisting of only two navigation satellites located around the Earth-Moon L1,2 libration points is obtained for the Universe Lighthouse. In order to determine the feasible constellations that can achieve continuous global coverage for lunar orbits, an exhaustive search over all possible combinations of libration point orbits is performed first. With the use of a fitting procedure, amplitude relations between the feasible L1 and L2 libration point orbits are derived by polynomial interpolation. After that, a cislunar navigation simulation is conducted to verify the navigation performance of the candidate two-satellite constellations. The final Monte Carlo simulation results indicate that the simplified system is available for cislunar navigation and the best accuracy of a few tens of metres can be achieved for both the trans-lunar cruise phase and lunar orbit phase.

The situation today can be described as very frustrating for a variety of reasons. Air traffic flow-management (ATFM) has dominated the scene for many years since its conception in 1980. At that time, the principles of ATFM were directed at ensuring that temporary or isolated sector overloads could be handled by ATC and only when broad, prolonged overloads were expected was ATFM activated. Today, we have the reverse situation, where ATFM is active throughout 16 h or more during each day. The system as such was never intended or planned to cope with such a burden and the results are seen in a variety of forms, including departure delays as shown in Fig. 1.