With the improvement of the bias instability of Micro-Electromechanical Systems (MEMS) gyroscopes, the g-sensitivity error is gradually becoming one of the more important factors that affects the dynamic accuracy of a MEMS gyroscope. Hence there is a need for correcting the g-sensitivity error. However, the traditional calibration of g-sensitivity error uses a centrifuge. The calibration conditions are harsh, the process is complex and the cost is relatively high. In this paper, a fast and simple method of g-sensitivity error calibration for MEMS gyroscopes is proposed. With respect to the bias and random noise of a MEMS gyroscope, the g-sensitivity error magnitude is relatively small and it is simultaneously coupled with the Earth's rotation rate. Therefore, in order to correct the g-sensitivity error, this work models the calibration for g-sensitivity error coefficients, designs an (8+N)-position calibration scheme, and then proposes a fitting method for g-sensitivity error coefficients based on the Newton iteration and least squares methods. Multi-group calibration experiments designed on a MEMS Inertial Measurement Unit (MEMS IMU) product demonstrate that the proposed method can calibrate g-sensitivity error coefficients and correct the g-sensitivity error effectively and simply.

Retrospective analysis of the Total Loss and Serious Casualty Rate (TL/SC Rate) for UK registered deep-sea and inshore fishing vessels over a twenty-year period (1961–80) revealed a gradual and sustained increase.

The mean TL/SC rate for 1971–80 (6·041/1 000 vessels at risk) was almost 70 percent higher than the corresponding mean for the previous decade (3·79/1000 vessels at risk) and this difference was statistically significant (p < 0·05).

Subsequent examination of vessel losses and casualties by cause indicate that 64 per cent of this detected increase was due to a concomitant increase in vessels lost or damaged due to foundering (particularly inshore vessels) and that the mean vessel age at loss from this cause was 24 years old. Synthesis of available evidence relating to the onset of this increase (1971); mean age at loss due to foundering (24 years); and the current age structure of the fleet, supports the hypothesis that the increase in founderings in the early 1970s may be explained partly by a cohort effect resulting from the uncontrolled fleet rebuilding programme almost a quarter of a century earlier in the immediate post-war period.

Current combined risks of fishing vessel loss and casualty are about twice as great overall as those with which the Committee of Inquiry into Trawler Safety (1969) was concerned and over which it expressed deep concern.

When two ships encounter one another at sea, there is a possibility that they will collide. Whether there is actual danger or not depends on the physical facts of their respective positions and motions. If danger does exist, the motions must be changed. The purposes of Dr. Morrel's paper are (1) to inquire what facts must be known, both to distinguish the cases of actual danger and to choose effective remedial action; (2) to determine when and how well these facts must be known; and (3) to consider how these facts may be obtained and how they may be best utilized.

The paper attempts to construct an integrated treatment of the whole problem, in terms of the fundamentals that define its nature and shape its solution. The problem is large and complex. Consequently, a compact treatment of it must perforce omit most of the details; both of the evidence and analysis by which the principles are established and of the technology by which they may be exploited.

Much of the treatment uses mathematics; but emphasis is placed on the implications rather than on procedures.

The paper was presented at the meeting of the Ausschuss für Funkortung held at Kiel on 10, 11, 12 September 1960 and is printed with that body's kind permission.

For marine traffic engineering, traffic surveys are most important and provide the fundamental materials necessary for harbour and fairway design, traffic control planning, &c. Such surveys cover numerous items, the main subjects being traffic volume, speed, distribution of ships' tracks, origin and destination and type of cargo. Since we have to deal with many vessels, handled by people with varying temperaments, knowledge and ability, observations usually show a wide scatter; the object is often to find some formula or rule to explain the phenomena, and traffic surveys are therefore apt to prove both expensive and time consuming. When, for example, Yamaguchi and others conducted a year long observation on traffic in the Akashi Channel in 1963 at least two members of the team stood watch for 24 × 365 hours in a hillside cottage making both visual and radar observations. Since then the survey has been extended to more than ten other straits well known for difficulties in manœuvring.

Within the University of Wales Institute of Science and Technology, a general study of navigation has led to a review of error distributions which has now reached the stage at which comment on a wide front would be particularly welcome. The work has been undertaken by Wing Commander E. W. Anderson who, with the generous permission of Smiths Industries Limited, is writing a thesis for the Department of Maritime Studies, and by D. M. Ellis, Lecturer in Statistics in the Department of Mathematics. In the first half of this paper, Anderson emphasizes the distinction between distributions involving one item or identical items and those involving a number of items which, though nominally the same, are in fact diverse. In the second half of the paper (from Section 8 on), Ellis shows how the apparent variation of results that arise in practice may be unified into a simple inclusive pattern.

The first step was to investigate the distributions that arise in practice. It was decided that the pages of this Journal would make ideal witnesses because they provide a broad sample and are impartial. From these pages every distribution was extracted which involved more than fifty observations and whose pattern was not markedly skew. The distributions were transferred to log-linear graph paper so that the horizontal error scale was linear and the probability of each error was plotted on the vertical logarithmic scale.

To meet the accuracy, integrity, continuity and availability required for many navigation applications the Locata technology can provide an alternative to satellite-based navigation in difficult Global Navigation Satellite System (GNSS) signal environments, especially for applications in port areas and in constricted waterways. Unlike GNSS constellations, a LocataNet – a local constellation of LocataLites – can be designed specifically for different environments to avoid signal blockages, interference or poor geometry. By using Locata technology, the optimal performance within particular areas can always be guaranteed. This paper demonstrates the influence of LocataNet configuration on the reliability and integrity of the Locata positioning system. The performance of the Locata system is investigated using the Receiver Autonomous Integrity Monitoring (RAIM) concept. Fault Detection and Exclusion (FDE) algorithm performance is validated through the computation of the Dilution of Precision (DOP), the Horizontal Protection Level (HPL) and the correlation coefficient between two failure modes that can indicate the quality of fault identification. The experimental analysis shows that a good configuration of LocataLites will enhance the accuracy and reliability of the navigation system.

The satellite constellation with automatic dependent surveillance-broadcast on-board is of great importance for air traffic surveillance due to its multiple advantages compared with traditional methods. Although some research has been conducted on satellite constellation design based on coverage performance, the findings cannot entirely satisfy all the requirements of air traffic surveillance owing to the lack of analysis on inter-satellite links and network transmission. This paper presents a novel design of a low earth orbit satellite constellation network to solve this problem. Based on the requirements of space-based surveillance, an evaluation model of constellation performance is proposed concerning coverage, link and transmission. The simulation results show that the evaluation model can reflect the performance of a satellite constellation network designed for a space-based surveillance system, and a 55-satellite constellation design scheme with fairly good performance can fulfil the function of global real-time air traffic surveillance.

For certain applications such as E911/E999/E112, GPS chipset receiver manufacturers will possibly have to test their products to ensure these fulfill mandated performance specifications for a variety of outdoor and indoor conditions. As opposed to testing in the field, laboratory testing is totally repeatable and controllable, and may be less costly. Hardware GPS signal simulators are now able to simulate signals under a variety of attenuation and multipath conditions. In indoor environments, GPS signals suffer not only from severe attenuation and multipath but from complex variations thereof. A method to simulate indoor GPS signals such that the stochastic characteristics of the simulated signals match those of actual GPS signals received in situ by a high sensitivity GPS receiver in various indoor environments is presented. Probability density functions and correlation coefficients are used to demonstrate the similarity between field and simulated data in terms of signal power fading and estimated pseudorange error. The results clearly demonstrate the feasibility of the approach.

This paper focuses on modelling and predicting differential GPS corrections transmitted by marine radio-beacon systems using artificial neural networks. Various neural network structures with various training algorithms were examined, including Linear, Radial Biases, and Feedforward. Matlab Neural Network toolbox is used for this purpose. Data sets used in building the model are the transmitted pseudorange corrections and broadcast navigation message. Model design is passed through several stages, namely data collection, preprocessing, model building, and finally model validation. It is found that feedforward neural network with automated regularization is the most suitable for our data. In training the neural network, different approaches are used to take advantage of the pseudorange corrections history while taking into account the required time for prediction and storage limitations. Three data structures are considered in training the neural network, namely all round, compound, and average. Of the various data structures examined, it is found that the average data structure is the most suitable. It is shown that the developed model is capable of predicting the differential correction with an accuracy level comparable to that of beacon-transmitted real-time DGPS correction.

The predictions of Length-Of-Day (LOD) are studied by means of Gaussian Process Regression (GPR). The EOP C04 time-series with daily values from the International Earth Rotation and Reference Systems Service (IERS) serve as the data basis. Firstly, well known effects that can be described by functional models, for example effects of the solid Earth and ocean tides or seasonal atmospheric variations, are removed a priori from the C04 time-series. Only the differences between the modelled and actual LOD, i.e. the irregular and quasi-periodic variations, are employed for training and prediction. Different input patterns are discussed and compared so as to optimise the GPR model. The optimal patterns have been found in terms of the prediction accuracy and efficiency, which conduct the multi-step ahead predictions utilising the formerly predicted values as inputs. Finally, the results of the predictions are analysed and compared with those obtained by other prediction methods. It is shown that the accuracy of the predictions are comparable with that of other prediction methods. The developed method is easy to use.

Ionospheric disturbances affect Global Positioning System (GPS) performance in terms of accuracy and integrity, especially over the equatorial region. During the period of the disturbances, GPS receivers suffer from a high noise level. Not taken into account by the current stochastic model, the ionospheric disturbances degrade GPS positioning accuracy. In addition, non-Gaussian tails are observed in the distribution of the noise during the period of the disturbances; therefore the integrity of GPS can also be affected. This paper develops a statistical solution that is able to mitigate effects of ionospheric disturbances on GPS accuracy and integrity using a commercial dual frequency receiver. The Rate of Total Electron Content (TEC) change Index (ROTI), a parameter derived from the dual frequency receiver, is used to group the levels of ionospheric disturbances. The standard deviations of the pseudorange noise under different groups are evaluated. By incorporating both the ROTI and the satellite elevation, a modified stochastic model is proposed to reduce the effect of the disturbed observation on the positioning accuracy. The performance of the model is evaluated by a test and an inflated sigma for each group is recommended for over-bounding anomalies of observations to protect the user against threats from ionospheric disturbances. This technique, together with results in this paper, can be applied to mitigate the effects of ionospheric disturbances on GPS.

Integrating the visual navigation mechanism of flying insects with a nonlinear Kalman filter, this paper proposes a novel navigation algorithm. New concepts of entropic map and entropy flow are presented, which can characterize topographic features and measure changes of the image respectively. Meanwhile, an auto-selecting algorithm of assessment threshold is proposed to improve computational accuracy and efficiency of global motion estimation. The simulation results suggest that the navigation algorithm can perform real-time rectification of the missile's trajectory well, and can reduce the cost of the missile's hardware.

An approach formulated by vector algebra is proposed to deal with great circle sailing problems. Using the technique of the fixed coordinates system and relative longitude concept, derivations of formulae for this approach are simpler than those of the conventional methods. Due to fixing the initial great circle course, the great circle track (GCT) is determined. Since the course is fixed (known as “COFI” in this paper), the proposed approach, which we have named the “COFI method”, can directly calculate the waypoints along the GCT. It is considered that the COFI method is a more understandable and straightforward method to solve waypoint problems than older approaches in the literature. Based on the COFI method, a program has been developed for the navigator. In addition, the spherical triangle method with respect to the equator crossing point (STM-E) is developed by supplemental theorem. Several examples are demonstrated to validate the proposed COFI method and STM-E.

The demand for accurate indoor positioning continues to grow but the predominant positioning technologies such as Global Navigation Satellite Systems (GNSS) are not suitable for indoor environments due to multipath effects and Non-Line-Of-Sight (NLOS) conditions. This paper presents a new indoor positioning system using artificial encoded magnetic fields, which has good properties for NLOS conditions and fewer multipath effects. The encoded magnetic fields are generated by multiple beacons; each beacon periodically generates unique magnetic field sequences, which consist of a gold code sequence and a beacon location sequence. The position of an object can be determined with measurements from a tri-axial magnetometer using a three-step method: performing time synchronisation between sensor and beacons, identifying the beacon field and the beacon location, and estimating the position of the object. The results of the simulation and experiment show that the proposed system is capable of achieving Two-Dimensional (2D) and Three-Dimensional (3D) accuracy at sub-decimetre and decimetre levels, respectively.

This paper focusses on the development of a tool for decision-making, tailored for personnel involved in complex Ship-To-Ship (STS) operations, to enhance the efficiency and safety of these operations. A step-wise approach has been selected. The first step includes specification, development and testing of the tool in a simulated work environment using full-mission simulators. In the second step the findings from application of the tool in the simulated work environment will be used to develop a prototype which will be tested during real life STS operations. This paper describes work done in the first of these two steps. During four iterations, a Graphical User Interface (GUI) has been made following Interaction Design (IxD) principles. The designs have been iteratively developed and tested by experienced ship's officers in a ship-handling simulator to clarify key information to enhance their Situation Awareness (SA) and decision-making process. In order to find indicators for performance, an initial performance test was carried out in a ship-handling simulator. The test indicates that a logic based Decision-Support System (DSS) can improve existing simulator-based training activities in STS operations.

Current Motion Compensation (MOCO) methods using Inertial Navigation System (INS)/Global Positioning System (GPS) integrated systems have provided an important advance in Synthetic Aperture Radar (SAR) imagery, but most of these methods only work well over a short imaging period. With the development of high-resolution SAR that provides image gathering over long periods, the need for higher levels of INS/GPS performance than normally available is desired. The higher requirement of INS/GPS for SAR MOCO is two-fold: (1) the accurate knowledge of location information, and (2) the smoothness of relative change in navigation error. In this paper, we design an INS/GPS architecture with dual-filter correction to obtain accurate absolute velocity and position measurement information with smooth low relative error noise over a long image gathering period. Real SAR data experimental results show that the proposed method effectively improves the MOCO performance of INS/GPS with long SAR imaging periods, in which the SAR azimuth resolution reaches 1·45 m, which is very close to the design value of 1 m.

Studies have already been published on the probability of collision at sea, the effect of darkness and reduced visibility on the probability of collision, and on the distribution of collisions in particular areas. Only Minorsky and Comstock appear to have studied the extent of the resulting damage and sufficient data are not available for detailed analysis.

The establishment and operation of any traffic management system calls for a considerable outlay, so that an objective estimate of the extent of collision losses is often required. Such a cost/benefit survey was carried out by the Japan Transport Economics Research Centre on the assumption that a traffic management system can greatly reduce the incidence of collisions involving vessels of over 3000 g.r.t. Since half the aggregate loss is shown to relate to these large vessels (and considering their increasing capital value), an expenditure of ten billion yen or more (£20 million) over a period of ten years would appear to be cost effective if its primary purpose were to avert accidents to large vessels.

The accurate, continuous determination of position, heading and course at all times, under all normal operational conditions, would be very desirable. This ideal has not been achieved for flights or voyages of long duration, but the many developments of recent years begin to give some promise that it may be possible. For high altitude aircraft the continuous optical observation of celestial bodies offers an evident solution, and doppler systems can give continuous speed over ground. For ships, however, the attainment of such an ideal navigation system is difficult. The various shore-based radio navigation systems have made important contributions, as have the development of inertial techniques. In addition, automatic optical sextants have been developed which can be used in clear weather.

This paper is the fourth chapter of a series on Air Navigation Systems during theperiod from the early oceanic flights and the inception of commercial aviation to the introduction of INS in civil aircraft. Comments on the content of the paper would be welcomed by the author and the editor.

A direct method for obtaining the two possible positions derived from two sights using vector analysis instead of spherical trigonometry is presented. The geometry of the circle of equal altitude and of the two body fixes is analyzed, and the vector equation for simultaneous sights is constructed. The running fix problem is also treated.