The September 2002 issue of The Journal included a paper that implied that the US practice of negotiating collision avoidance manoeuvres by VHF had effectively been endorsed by the IMO. That view is challenged, by reference to the relevant provisions in the US legislation, the COLREGS and chapter IV of the SOLAS Convention. This paper also concludes that AIS will be a useful tool to provide additional information, but should not alter the way in which the COLREGS are to be applied.

This paper examines the evidence to support the view that the inability of seamen to determine accurate longitude at sea in sailing ships was a major factor in the loss of ships and crews that was effectively solved by the introduction of the marine chronometer. It concludes that this was not the case and that a more compelling factor for the safety of ships was the introduction of mechanical propulsion systems.

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.

Automatic Dependent Surveillance Broadcast (ADS-B) Out supports various ground applications including Air Traffic Control (ATC) surveillance in radar airspace, non-radar airspace and on the airport surface. In addition, the capability of aircraft to receive ADS-B Out messages from other aircraft within their coverage (ADS-B In) enables enhanced airborne surveillance applications. The requirements of the application vary depending on its safety-criticality. More stringent applications will require higher levels of performance. It is therefore critical that the ADS-B system performance is measured against the most stringent application it is designed for. This paper reviews the various enhanced airborne surveillance applications and the required ADS-B information to support them. It identifies the ADS-B based applications required for Air Traffic Management (ATM) modernisation under the SESAR/NextGen programs. It discusses existing ADS-B Out versions and their capabilities. A mapping exercise is undertaken to assess the credibility of the ADS-B system performance to support the functionalities and requirements of the various enhanced airborne surveillance applications and establish those that require further research and development, highlighting some of the key challenges.

Alternative Binary Offset Carrier (AltBOC) modulation signal has the constraint of an equal power allocation scheme. Thus, it is not flexible enough to meet different requirements. To solve this problem, we propose a General AltBOC (GAltBOC) modulation. The proposed technique can achieve the same function as AltBOC. Meanwhile, its power allocation ratio can be adjusted when required. The detailed derivation of the GAltBOC modulation is presented, and three representative cases as well as the signal properties are discussed. To further improve the combination efficiency, we develop the Interlacing GAltBOC (IGAltBOC) modulation based on the GAltBOC modulation. The Power Spectrum Density (PSD) and correlation functions of the proposed signals are verified by simulation. The code tracking error and implementation complexities are analysed and compared with existing methods. Results show the proposed signals indeed enhance the flexibility of power allocation ratio with the same level code tracking accuracy. Compared with AltBOC modulation, the proposed signal can reach a higher combination efficiency at the expense of relatively higher implementation complexity. Compared with Asymmetric Constant Envelope Double-sideband (ACED) modulation, the proposed signals have significantly lower complexity of signal generation, which is helpful in simplifying the signal generation in the payload transmitter.

The modernisation of GPS and the introduction of Galileo will introduce the use of Binary Offset Carrier (BOC) modulation. BOC will be implemented as either a sine or cosine sub-carrier modulation, which affects the spectral properties of the signal and the receiver search, acquisition and tracking processes. This paper addresses the effect of the various forms of BOC modulation on the receiver search process. Theory is developed to draw comparisons between search techniques and verified with computer simulation models.

An adaptive Kalman filtering approach is proposed for attitude determination to replace the fixed (conventional) Kalman filtering approach. The filter is used to adaptively reflect system dynamics changes or rapid changes in vehicle trajectory. The estimation procedure is carried out through the use of a measurement residual sequence. The sequence is used as a piece-wise stationary process inside an estimation window. The measurement noise covariance matrix and the system noise matrix are adaptively estimated. An extended Kalman filter approach with iteration of the states within-an-epoch was performed to overcome the non-linearity of the observation equations. A test was performed to evaluate the proposed technique. Different trajectory scenarios are presented to show the difference in performance between the adaptive Kalman filter and the conventional one. Results show that the proposed adoptive filtering approach has a better performance than the conventional filter.

Assisted-Global Navigation Satellite Systems (A-GNSS), or Assisted-Global Positioning Systems (A-GPS) in particular, are now commonly accepted as an effective way to reduce the time-to-first-fix (TTFF) in GNSS-unfriendly environments, e.g. in areas of weak GNSS signals. Today's location-based service (LBS) devices such as GPS-enabled mobile phones and personal digital assistants (PDA) rely on A-GPS; however, such commercial devices are equipped with an integrated A-GPS chip that makes customisation very difficult. The Open Source GNSS Reference Server (OSGRS) provided by the University of New South Wales is an open source Java application that can generate the necessary data for A-GPS clients. The GNSS Reference Interface Protocol (GRIP), based on extensible mark-up language (XML), is employed as the OSGRS interface protocol. This paper describes the current status of OSGRS: a client simulator is available open-source; client software which supports four different types of A-GPS-enabled receivers has been developed and used to test OSGRS. The performance of the OSGRS is analysed based on intensive tests. The challenges for OSGRS and future work are also discussed.

This paper presents an investigation of the precise point positioning (PPP) performance of a combined solution from BDS-2 and BDS-3 satellites. To simultaneously process different BDS signal observations, i.e., B1/B1C, B2/B2a and B3C, undifferenced and uncombined observations with ionosphere delay constrained by the deterministic plus stochastic ionosphere model are used in the basic model. Special attention is paid to code bias and receiver clock parameters in the derivation of the observation model. The analysis is carried out using more than one-month data for BDS-2 and BDS-3 collected at the CANB, DWIN, KNDY and PETH stations in the Asia-Pacific region. The results suggest that compared with BDS-2 alone, the BDS-2 and BDS-3 solution provides significantly more accurate PPP, with increases of 28%, 21% and 5% in the up, north and east directions, respectively. In addition, the average root mean square error decreases to 0·21, 0·13 and 0·16 m for the three directions. Furthermore, the PPP convergence time for BDS-2 and BDS-3 is about 1·5 h and less than 1 h for the horizontal and vertical components, respectively, whereas that for BDS-2 alone is about 2·3 h for both directions.

To satisfy the needs of precise pin-point landing missions in deep space exploration, this paper proposes a method based on feature line extraction and matching to estimate the attitude and position of a lander during the descent phase. Linear equations for a lander's motion parameters are given by using at least three feature lines on the planetary surface and their two-dimensional projections. Then, by taking advantage of Singular Value Decomposition (SVD), candidate solutions are obtained. Lastly, the unique lander's attitude and position relative to the landing site are selected from the candidate solutions. Simulation results show that the proposed algorithm is able to estimate a lander's attitude and position robustly and quickly. Without an extended Kalman filter, the average errors of attitude are less than 1° and the average errors of position are less than 10 m at an altitude of 2,000 m. With an extended Kalman filter, attitude errors are within 0·5° and position errors are within 1 m at an altitude of 247·9 m.

The Micro-Nano satellite TianTuo-3 (TT-3) developed by the National University of Defense Technology (NUDT) was successfully launched on 20 September 2015. The space-based Automatic Identification System (AIS) on board TT-3 works well and stably receives AIS signals from global vessels. In this work, we perform statistical analysis on the detection probability of the vessels in the concerned areas by using the TT-3 AIS data. The results suggest that the detection probability of vessels decreases as the distribution density increases, especially in the offshore areas of dense traffic and the TT3-AIS vessel detection probability in the oceans can be higher than 40%, indicating that the TT-3 AIS has achieved a high probability of coverage of vessels for a single receiving antenna. The analysis results will present helpful references both in evaluating the potential application of satellite-based AIS and for designing the next generation space-based AIS which might greatly improve the detection probability of ocean-going vessels.

Nowadays, the most widely used method for estimating location of autonomous vehicles in real time is the use of Global Navigation Satellite Systems (GNSS). However, positioning in urban environments using GNSS is hampered by poor satellite geometry due to signal obstruction created by both man-made and natural features of the urban environment. The presence of obstacles is the reason for the decreased number of observed satellites as well as uncertainty of GNSS positioning. It is possible that in some sections of the vehicle route there might not be enough satellites necessary to fix position. It is common to use software for static GNSS measurement campaign planning, but it is often only able to predict satellite visibility at one point. This article presents a proposal for dynamic GNSS mission planning using a Digital Terrain Model (DTM) and dead reckoning. The methodology and sample results of numerical experiments are also described. They clearly show that proper dynamic GNSS mission planning is necessary in order to complete a task by an autonomous vehicle in an obstructed environment.

One of the issues regarding integrated GPS/pseudolite measurements is how to deliver a pseudolite's position to a receiver or to post-processing software and how to manage it. This paper presents a proposed solution to this problem. The standard navigation message is modified in such way that without changing receivers (or post-processing software), the calculated position of a transmitter is fixed at a pseudolite's known position. The formulae for modification of standard Ephemeris Data are also derived. This algorithm can be implemented in a transmitter's firmware or a navigation data file can be modified for post-processing.

A localization system using GPS, ABS sensors and a driving wheel encoder is described and tested through real experiments. A new odometric technique using the four ABS sensors is presented. Due to the redundancy of measurements, the precision is better than the method using differential odometry on the rear wheels only. The sampling is performed when necessary and when a GPS measurement is performed. This implies a noticeable reduction of the GPS latency, simplifying the data-fusion process and improving the quality of its results.

This research aims to test the suitability of a protocol for automated measurement to describe visual and motor behaviour in the process of learning to sail. The objective is to provide coaches with the necessary scientific and technological support to analyse the variables of success in race starting. The study was performed with a highly ranked sailor in the Optimist class ranking. The instruments used to carry out the investigation were the sailing simulator VSail-Trainer® and the eye tracking system ASL®. Two simulated race starts were performed with a protocol of five minutes. The results show the automated protocol is suitable for measuring the ability of boat handling and visual performance in simulated conditions. Visual behaviour shows that the sailor visually fixates on locations that provide relevant information for the race start such as clock, other competitors, wind direction and the start buoys.

To solve the problem of attitude determination using magnetometers independently and uniquely, which is important for underwater vehicles, a type of full attitude determination method based on geomagnetic gradient tensor is proposed in this paper. In this method, a group of non-linear equations concerning geomagnetic gradient tensors is established, where a quaternion is selected to calculate three attitude angles of an underwater vehicle. The optimal quaternion is estimated using Newton Down-hill to optimise the object function. The detailed steps of the full attitude determination based on geomagnetic gradient tensor are given, and the effects of the initial angle error and the sensor noise on the attitude determination are investigated. Simulations show that the algorithm can identify precisely and quickly the attitudes even in the presence of larger initial angle error and sensor noise, which proves the attitude determination algorithm.

Most reference books or monographs about the history of the gyrocompass portray individual inventors, each as an inventive genius, respected as a national hero and probably depicted creating novelties in ‘brooding meditation’. This seems to be an accepted, rather comfortable point of view, as the subject covers the invention of a ‘black-box’-type too. But the invention, development and the adaption of this gyro instrument in a complex technological and social system was not achieved on the basis of a ‘single-handed’ venture.

If emerging technologies are not only scientific, but also involve social or cultural requirements, then communication along the networks of knowledge between inventor, mechanic and mathematician, the code of patent lawyers and financiers and – last but not least – navigation officers and the red tape of a navy must play an influential role. I would thus like to sketch out the subject of invention as communication and present the inventor as a navigator, someone who leads his crew through all currents, shallows and drifts and, while keeping ahead of other competitors, arrives at some still uncertain location.

An evaluation method named vague set is proposed to describe the suitability of a geomagnetic map. It is based on the Fuzzy Decision Making (FDM) method, and overcomes the FDM model's shortcomings that favouring and opposing content cannot be taken into account simultaneously. The membership function and non-membership function are used to define the influence of the geomagnetic map parameters on map suitability, including standard deviation, information entropy, roughness and slope variance. The weight of each geomagnetic map parameter is calculated by establishing an optimisation model. Vague set data are divided into four types after classification, and Weighted Score Function Values (WSFVs) of matching areas are obtained by using the Weighted Score Function (WSF) method. Then, WSFV of each matching area are compared to select an optimal area. Simulation results demonstrate that geomagnetic map suitability is positively proportional to the function value, and matching error is negatively proportional to the WSFV of the matching area.

The neural networks (NN)-based geometry classification for good or acceptable navigation satellite subset selection is presented. The approach is based on classifying the values of satellite Geometry Dilution of Precision (GDOP) utilizing the classification-type NNs. Unlike some of the NNs that approximate the function, such as the back-propagation neural network (BPNN), the NNs here are employed as classifiers. Although BPNN can also be employed as a classifier, it takes a long training time. Two other methods that feature a fast learning speed will be implemented, including Optimal Interpolative (OI) Net and Probabilistic Neural Network (PNN). Simulation results from these three neural networks are presented. The classification performance and computational expense of neural network-based GDOP classification are explored.

It has hitherto been generally presumed that the division of the horizon into thirty-two points was a development of the late medieval period. Such a division, it has been said, was impossible in the pre-compass era. ‘It is questionable whether even so many as sixteen directions could have been picked out and followed at sea so long as Sun and star, however intimately known, were the only guides’, one eminent authority has declared; ‘Even the sailors in the north-western waters had only four names until a comparatively late date.’ Chaucer's reference in his Treatise on the Astrolabe to the thirty-two ‘partiez’ of the ‘orisonte’ has for long been quoted as the earliest evidence on the subject. The Konungs Skuggsjà, a thirteenth-century Norwegian work, however, refers to the Sun revolving through eight œttir; and the fourteenthcentury Icelandic Rímbegla talks of sixteen points or directions. An important discovery by the distinguished Danish archaeologist, Dr. C. L. Vebæk, in the summer of 1951, brings a new light to the whole problem and makes the earlier held view scarcely tenable. Vebæk was then working on the site of the Benedictine nunnery (mentioned by Îvar Bárdarson in the mid-fourteenth century) which stands on the site of a still older Norse homestead on the Siglufjörd, in southern Greenland. Buried in a heap of rubbish under the floor in one of the living-rooms, together with a number of broken tools of wood and iron (some of them with the owner's name inscribed on them in runes) was a remarkable fragment of carved oak which evidently once formed part of a bearingdial. This was a damaged oaken disk which, according to the archaeologists, dates back to about the year 1200.