Digital Selective Calling (DSC) is causing serious problems for Search and Rescue (SAR) providers. Administrations must seriously consider the humanitarian and legal implications of continuing the implementation of DSC. They may be in violation of the Safety of Life at Sea Convention, the International Convention on Maritime Search and Rescue, 1979, and the United Nations Convention on the Law of the Sea, 1982, by knowingly implementing communications technology that may jeopardize lives at sea even though the primary intent of DSC is to establish a suitable distress alerting method. States may very well open themselves to legal liability if loss of life or environmental damage can be linked in any way to the known faults of DSC.

In the field of modernised Global Navigation Satellite System (GNSS) signal design, several Dual-frequency Constant Envelope Multiplexing (DCEM) methods have been recently proposed. However, the existing DCEM methods, such as Alternative Binary Offset Carrier (AltBOC), generalised AltBOC and Asymmetric Constant Envelope Binary Offset Carrier (ACE-BOC), are only applied in some special cases. In this paper, we present a unified DCEM design framework for GNSS signals. The existing DCEM methods can be unified in this framework. First, the signal components at two carrier frequencies are combined into two single-frequency constant envelope signals. Then, the linear sum of dual-frequency signals with non-constant envelopes is obtained. Finally, the linear sum is converted into the corresponding DCEM signal by solving an optimisation problem. The proposed design framework has no strict constraints on the number, power ratio and phase relationship of the signal components. Moreover, some special design cases under this framework are also analysed in detail. The analytical results show that the proposed design method can reach higher multiplexing efficiency compared with the existing methods. Based on the proposed method, we suggest a scheme to multiplex the BeiDou regional signals and global signals at the B2 frequency. The simulation results of correlation functions and Power Spectrum Density (PSD) verify the correctness and effectiveness of the proposed design method.

This paper describes three different antenna systems for mobile vehicle applications. The antennas are either patches or derivatives in all cases. The first is a dual-band telephone antenna with a low profile and wide bandwidth. Operating at 900 MHz and 1800 MHz, with a VSWR of better than 1·7, it is a hybrid construction combining a monopole with a top-loading patch shorted to the ground-plane. Extra-shorted pins provide the upper frequency band coverage. It provides monopole radiation characteristics and can be hidden under a plastic panel or mounted on the vehicle roof. The second is a microstrip patch antenna integrated into a laminated glass windscreen for a vehicle. It is fed using a coplanar waveguide feed printed on the innermost layer of the glass, avoiding the need for a contacting feed within the laminate. The patch and ground plane are meshed for manufacturing in the glass to avoid distorting the heat profile when the glass is shaped and laminated. The patch is easily fed from inside the vehicle and is potentially a very low cost design. The final antenna discussed is a dual-band patch antenna specifically designed for the Globalstar satellite telephone system at 1·6 GHz and 2·45 GHz. It also covers the Iridium band at 1·6 GHz. A single circularly polarised patch is used. Dual-band operation results from truncating the corners of the square patch and judiciously placed slots to achieve a band spacing of 1·5.

A variety of operational systems are vulnerable to disruption by solar disturbances brought to the Earth by the solar wind. Of particular importance to navigation systems are energetic charged particles which can generate temporary malfunctions and permanent damage in satellites. Modern spacecraft technology may prove to be particularly at risk during the next maximum of the solar cycle. In addition, the associated ionospheric disturbances cause phase shifts of transionospheric and ionosphere-reflected signals, giving positioning errors and loss of signal for GPS and Loran-C positioning systems and for over-the-horizon radars. We now have sufficient understanding of the solar wind, and how it interacts with the Earth's magnetic field, to predict statistically the likely effects on operational systems over the next solar cycle. We also have a number of advanced ways of detecting and tracking these disturbances through space but we cannot, as yet, provide accurate forecasts of individual disturbances that could be used to protect satellites and to correct errors. In addition, we have recently discovered long-term changes in the Sun, which mean that the number and severity of the disturbances to operational systems are increasing.

Map matching is an important algorithm for any location-based service, especially in navigation and tracking systems and services. Identifying the relevant road segments accurately and efficiently, given positioning data, is the first and most important step in any map matching algorithm. This paper proposes a new approach to searching for road candidates by clustering and then searching road segments through a constructed hierarchical clustering tree, rather than using indexing techniques to query segments within a fixed search window. A binary tree is created based on the hierarchical clustering tree and adaptive searches are conducted to identify candidate road segments given GPS positions. The approach was validated using road maps with different scales and various scenarios in which moving vehicles were located. Both theoretical analysis and experimental results confirm that the proposed approach can efficiently find candidate road segments for map matching.

Over the past ten years at least the Law of the Sea has been a subject of continuing debate. This would have been inevitable even if there had been no UN Law of the Sea Conference to focus people's minds; the increasing importance of offshore hydrocarbon deposits, the potential exploitation of seabed mineral nodules and the competition to exploit fish stocks would have ensured that. Add to these factors the demands of the large number of newly formed coastal states, which did not see their interest well served by the law that had largely developed under the influence of the western maritime nations, and something clearly had to be done.

Many nations are debating the implementation of vessel traffic services (VTS) and it is envisaged that some regulation of the movement of marine traffic may soon be imposed. It is highly desirable that prior to any change a rigorous appraisal of the existing traffic be carried out to establish the level of risk in the area; this level can then be used to evaluate any proposed change. The following note describes a research project concerned with establishing a general method of determining the base risk level, developed from earlier research by M. Degré and M. Lefèvre who used a computer simulation of marine traffic in the Dover Strait to assess the impact of various suggested traffic separation schemes. A cost-effective tool has been developed at Liverpool which will enable traffic patterns to be studied in areas remote from the land. This is a computer simulation model which is being used to establish dynamic areas of risk in the Irish Sea, which could easily be transposed to study traffic patterns in any other area.

The paper proposes highly stable moored ocean platforms and a transatlantic submarine telephone cable to provide a reliable v.h.f. communication service and other A.T.C. facilities to civil aircraft on the main air routes across the North Atlantic. The main features of the platform and cable system are discussed and some idea of the time scale and costs is given.

The planning of facilities needed to enable future operations over the North Atlantic to accommodate reduced separation standards and to satisfy the specialized requirements associated with operating S.S.T. aircraft has emphasized the present unsatisfactory standard of communication services in the area.

One of the problems in arctic navigation by astro is the twilight period. At this time, if the Moon is below the horizon, suitable objects for sextant observation are not easy to find. The difficulty is aggravated by the fact that on certain flight paths the arctic twilight may last for many hours. It must also be remembered that in these areas the behaviour of the magnetic compass and of radio aids are often unreliable and this increases the relative importance of astro-navigation. With the introduction of the periscopic sextant into air navigation it has become possible to pre-set the instrument for a given star or planet and satisfactory observations may be possible when the heavenly body is still below the level of casual perception for the unaided eye. In this connection it is necessary to know what stars are likely to be seen under twilight conditions if efficient flight-planning is to be carried out.

Early in 1967, a few months before the restored Meridian Building of the Old Royal Observatory was opened to the public by Sir Richard Woolley, the Astronomer Royal, I received a visitor in my office then in the Meridian Building — later, I was to move to the west summer house of Flamsteed House. My visitor was Colonel Humphrey Quill, Royal Marines, Master of the Worshipful Company of Clockmakers that same year and author of the hook John Harrison, the Man who Found Longitude, which has become a standard work. He brought with him some manuscripts written by the subject of this lecture — Nevil Maskelyne, fifth Astronomer Royal, who lived in Flamsteed House for 46 years from 1765, making most of his important astronomical observations in the very building in which Col. Quill and I were sitting.

Global navigation satellite system (GNSS) receivers meet numerous challenges in a high-orbit environment, including weak and discontinuous signal, and time-varying strength. To resolve these issues and enhance reliability, an innovative adaptive vector tracking loop (VTL) scheme is proposed. Non-linear models of the VTL filter are established to calculate code phase and carrier frequency errors accurately. Based on this, a deep analysis has been developed on the measurement noise. To reduce the impact of the interdependent noises among channels in VTL, an adaptive VTL algorithm assisted by the variational Bayesian (VB) learning network is proposed to estimate the measurement noise and maintain the error convergence in the time-varying noise or signal outage conditions. Further, the implementation steps of the adaptive algorithm have been designed in detail. In particular, the carrier-to-noise power ratio (C/N0) estimation method is further employed to update the a prior probability density in case of change of tracking satellite. The simulation results indicate that the proposed VTL scheme with VB algorithm is a promising method to improve the accuracy and reliability of GNSS receivers significantly under a high-orbit degraded signal environment.

The geometry of the skeg in the Escort Tractor Voith tugs is the result of a series of intense investigations in the forms of the tug and its fins, oriented to get a significant improvement in the forces on the towing line when the indirect method is used in the escort towing. For that, and with the aim of getting the best behaviour of this fin, a variety of options have been investigated for years, evaluating its merits in terms of lift force and complexity to reach the present designs, which are adapted to the functions which the tug is destined to carry out. With the object of optimizing the lift force in the skeg when the indirect method is used in the escort towing, and after long investigations, the Voith Turbo Marine has incorporated a rotating cylinder at the leading edge to its design in escort towing for the first time at the beginning of 2005. The leading edge is the part over which the water flow first falls upon in normal escort operation conditions, calling this new development Voith Turbo Fin (VTF) to the system as a whole (skeg and rotating cylinder). This fin is analyzed in this article especially with regard to its basis, ways of operation and efficiency of the novel joining rotating cylinder.

This paper presents a description of a general method for the evaluation of marine collision risk. The approach differs considerably from existing methods in this area, in that it combines analytical modelling in a special way to analyse historical data. The method makes it possible to find the collision probability of a specific ship in any particular location, taking into account such location factors as area geometry, ship movements and speeds. It also constitutes a basis for worldwide data collection.

In view of the growth of marine traffic and the increase in the transportation of hazardous materials over the past two decades, considerable efforts are being made towards the development of maritime risk evaluation methods, the main objective being the quantification of ship collision probability. The methods developed to date can roughly be subdivided into the following two groups: (a) kinematic models (see for instance refs. 1–6); (b) historical data analysis (see for instance refs. 7–17). It is a well-established fact that most collisions are due to human failures, and it is widely accepted that human behaviour cannot be described well by mathematical formulae. Kinematic models are therefore not recognized as suitable for estimating this probability. Historical data analysis estimates the collision probability as the ratio of the number of observed collisions to the number of ship movements. Probabilities estimated in this way are only correct in a probabilistic sense when the assumption is satisfied that every ship movement has the same probability of collision. This assumption is rarely fulfilled since most ships often pass each other without collision danger. In addition, this approach is often hampered by lack of data for a specific traffic area, while the application of worldwide data cannot be considered realistic. As far as we know, there does not exist a method which can transfer, in a statistically justifiable manner, marine traffic data from one area to another. Moreover, neither of the above-mentioned approaches is appropriate to analyse alternative routes in the same area, or under changing circumstances.

The Navstar Global Positioning System (GPS) is a satellite-based passive radio-navigation system under development by the US Department of Defense (DOD) and due for operational deployment in the late 1980s. Each satellite carries an atomic frequency standard and transmits L-band spread-spectrum signals whose carrier frequencies and code epochs are synchronized with the satellite clocks. A suitably equipped user may measure the arrival time and frequency of the signals from at least four satellites to obtain accurate three-dimensional position and velocity information and, as a by-product, an accurate ‘system’ time.

D. H. Sadler has pointed out that the method I proposed in my paper (34, 247) can be improved, in his view, by the use of the formula

(1 + f) × distance = D.lat × sec(Co)

where the tabulation of Jean be found in his earlier paper (9, 371).

These two notes are the first of a series which will suggest to mariners the causes of collision at sea when radar is in use, by showing against each apparent cause an accumulation of court evidence and judgment, by isolating certain kinds of action which seem to have led to collision but have not been so regarded in every judgment and by examining certain judgments against a technically informed background.

In the articles which follow, a particular judgment is examined in the light of a more precise study of true motion as a direct source of intelligence at slow speeds, of plotting when courses and speeds are changing and of the suggestion that the Crossing Rules may be applied in fog after ‘ascertainment’.

The pioneers of air navigation used a simple magnetic compass as a heading reference. At first boat or surveying compasses were used but these were not really satisfactory for use in aircraft, as engine vibration caused them to rotate. The first successful magnetic compass for aircraft use was the Creigh–Osborne compass which took to the air on 27 October 1909, in the British Army Aeroplane flown by the celebrated Col. S. F. Cody. In the years following and throughout World War I magnetic compasses based on this early work, with either horizontal or vertical cards, were widely used.

Throughout the history of marine navigation it has been recognized by seamen that soundings of the sea bed are a most natural and valuable aid to safe passages. Yet it is probably true to say that the methods of obtaining such soundings and for recording and using the information so obtained remained relatively primitive for longer than any of the other arts or systems used by seamen.

Records can be found which indicate that the earliest navigators used poles or lines and plummets to measure the depths of water on the coasts and in the rivers. An example of the use of soundings by Phoenician seamen is recorded by Strabo, who relates that the captain of a Phoenician ship on a voyage to the Casseterides for tin thought himself too closely followed by a Roman ship and deliberately sought a shoal which he knew of on which to run his vessel to avoid capture and the loss of his precious secrets. Then Hanno, the famous Carthaginian admiral of about 500 B.C., at his furthest point south on the West Coast of Africa, outlined the contours of the River Niger, and the Greek admiral Nearchus at the same time made his voyage from the Indus to the Euphrates by soundings in the rivers and on the coast.