A dual-axis rotational Inertial Navigation System (INS) has received wide attention in recent years because of high performance and low cost. However, some errors of inertial sensors such as stochastic errors are not averaged out automatically during navigation. Therefore a Twice Position-fix Reset (TPR) method is provided to enhance accuracy of a dual-axis rotational INS by compensating stochastic errors. According to characteristics of an azimuth error introduced by stochastic errors of an inertial sensor in the dual-axis rotational INS, both an azimuth error and a radial-position error are much better corrected by the TPR method based on an optimised error propagation equation. As a result, accuracy of the dual-axis rotational INS is prominently enhanced by the TPR method, as is verified by simulations and field tests.

The fusion of multi-sensor data can provide more accurate and reliable navigation performance than single-sensor methods. However, the general Federated Kalman Filter (FKF) is not suitable for large changes of complex nonlinear systems parameters and is not optimized for effective information sharing coefficients to estimate navigation preferences. This study concerns research on the FKF method for a nonlinear adaptive model based on an improved Genetic Algorithm (GA) for the Strapdown Inertial Navigation System (SINS) / Celestial Navigation System (CNS) / Global Positioning System (GPS) integrated multi-sensor navigation system. An improved fitness function avoids the premature convergence problem of a general GA and decimal coding improves its performance. The improved GA is used to build the adaptive FKF model and to select the optimized information sharing coefficients of the FKF. An Unscented Kalman Filter (UKF) is used to deal with the nonlinearity of integrated navigation system. Finally, a solution and implementation of the system is proposed and verified experimentally.

Geostationary Earth Orbit (GEO) satellites play a significant role in the space segment of the Chinese Area Navigation System. The C-Band transfer ranging method developed by the National Time Service Center (NTSC) has been widely used in the Chinese Area Positioning System (CAPS), with its advantages of separating satellite ranging from time synchronization and being unaffected by weather. The explicit ranging correction models for the C-Band transfer ranging method are introduced in detail in this article for the first time. Precise Orbit Determination (POD) using C-Band pseudo-range observation of GEO satellite 2010-001A in July 2012 has been conducted. The residual Root Mean Square (RMS) of each site and POD are analysed with orbit difference over overlaps of adjacent orbit arcs. Moreover, the orbit of the GEO satellite has been evaluated by Satellite Laser Ranging (SLR) data from both domestic and foreign SLR sites for the first time. The residual RMS of POD using C-Band observation is better than 0·1 m, and the orbit difference over overlaps of adjacent orbit arcs is better than 3 m. In addition, the residual RMS in line-of-sight for a SLR site in China are better than 1 m, while the RMS for the Yarragadee site in Australia is about 3·4 m. It has been shown that the GEO satellite orbit accords very well with the C-Band observation. Also, the distribution of CAPS stations affects the orbit precision. All sites in CAPS are now located in China with low and medium latitudes. The residual RMS of the SLR site in the southern hemisphere is larger than that of the site in China.

The International Regulations for Preventing Collisions at Sea contain several important terms which are open to different interpretations such as ‘safe speed’, ‘close-quarters situation’ and ‘risk of collision’. It is not possible to give exact definitions of these terms as some of the factors involved are difficult to quantify but there is little doubt that mariners would welcome some official guidance on their application.

The following paper by Dr Hilgert proposes a method of defining ‘close-quarters situation’ in terms of the principal factors which apply. The method is of particular interest because it is actually used by the maritime administration of one government and has been submitted to the International Maritime Organization for consideration. The IMO Sub-Committee on Safety of Navigation has taken note of the suggested approach and has invited comments.

It is suggested in the paper that a simplified version of close-quarters situation could be determined in terms of the quantifiable parameters of speed, manoeuvrability and angle of approach. The method could be used to establish minimum values of a close-quarters situation but other factors would have to be taken into account such as the close presence of navigational hazards or other vessels, radar performance including the effect of errors and the desirability of keeping out of audible range of the fog signals of an approaching vessel.

Despite some obvious limitations the method serves to indicate the least values which should be used and the paper contributes to a better understanding of this aspect of the avoidance of collision at sea.

An Augmented Relative Navigation System (ARNS) is proposed for autonomous satellite formation flying in low-Earth-orbit (LEO). Inter-satellite ranging systems such as those based on radio frequency transmissions can provide additional observation information, e.g. inter-satellite distance measurement, which can be used to increase the Global Positioning System (GPS) stand-alone observation dimension, or treated as a non-linear equality constraint within a smoothly-constrained Kalman filter. Both approaches are implemented in the proposed ARNS described in this paper. An innovative phase integer ambiguity fixing and feedback scheme is implemented to increase the ambiguity fix rate of the GPS carrier phase measurements. A set of Gravity Recovery and Climate Experiment (GRACE) flight data is used to test and validate the relative navigation performance of the proposed methods. Results indicate that the augmented system can improve relative positioning accuracy by an order of magnitude.

Multipath is one of the main error sources in global navigation satellite system (GNSS) positioning. The high-resolution correlator (HRC) is a multipath mitigation technique well known for its outstanding performance for mid-delayed multipath, but still has a remaining error for the short-delayed multipath. This paper proposes a modified HRC scheme that can remove or reduce the error for short-delayed multipath signals. It estimates the HRC tracking error and augments the conventional HRC with the estimates. The method was implemented with a software receiver and the test results show short-delayed multipath-induced errors were reduced to about one third of those from the conventional HRC.

This paper investigates the problem of how to design the distance between a mobile buoy and the target to derive maximum positioning accuracy with a Moving Long Baseline (MLBL). To that end, the positioning model and the error sources of MLBL are derived, respectively. It is assumed that the position measurement of the mobile buoy and the distance measurement between the mobile buoy and the target are corrupted by white Gaussian noises, and the variance of the distance measurement is distance-dependent. Using tools from estimation theory, the Positioning Accuracy Metric (PAM) is designed with the distance error and the position errors are considered. Based on the PAM, the optimal distance between the mobile buoy and target is deduced when the mobile buoys are in optimal geometry. Simulation examples illustrate the results.

The routes of young, inexperienced pigeons released at four sites up to 13·5 km from the loft were recorded with GPS-based tracking devices. The routes were found to differ from those of old, experienced pigeons in several aspects: (1) Although being oriented when departing, young birds show more scatter and larger deviations from the home direction, but usually restrict their flights to a semicircle. (2) They apparently ignore prominent landmarks near the loft that are clearly visible. (3) Their tracks are typically more complex, consisting of a number of distinctive phases where the young birds head in different directions, which results in significantly longer routes, often exceeding the direct home distances more than four times. (4) At the same time, young birds seldom venture further away from the release site than the direct distance to home. Their behaviour can be interpreted as exploration to obtain new information on the distribution of navigational factors to be included in their still rudimentary navigational ‘map’. At the same time, their flights seem to include elements of safety, like anchoring the flights around the release site and a sense of distance, which help to reduce the chance of getting lost.

This paper presents an overview of results from the two year REGIONAL project. The aims of REGIONAL were to undertake research to enable landmarks to be an integral feature of future vehicle navigation systems. Results from the project, including five empirical road-based trials, are summarised. The main findings were: landmarks were widely used by drivers as key navigation cues; the incorporation of good landmarks within navigation instructions has the potential to considerably enhance vehicle navigation systems; although a wide range of landmarks are potentially useful to a driver, only a limited set, which displayed key characteristics, were consistently effective as navigation cues.

Serious accidents in the marine and offshore industry have underscored the need for safety evaluation of maritime operations using risk and safety analysis methods which have become a powerful tool in identifying technical solutions and operational management procedures. Given that Fault Tree Analysis (FTA) is a known methodology used for analysing engineering systems, the approach is usually conducted using known failure data. But most offshore operations are conducted in a challenging and uncertain environment and the failure data of some of these systems are usually unavailable requiring a flexible and yet robust algorithm for their analysis. This paper therefore seeks to analyse the complex structure of Offshore Supply Vessel (OSV) collision with platforms by incorporating a Fuzzy Fault Tree Analysis (FFTA) method. Fuzzy set theory provides the flexibility to represent vague information from the analysis process. The methodology is structured in such a manner that diverse sets of data are integrated and synthesized for analysing the system. It is envisaged that the proposed method could provide the analyst with a framework to evaluate the risks of collision enabling informed decisions regarding the deployments of resources for system improvement.

Marine accident frequencies reported in 20 different sources have been studied and compared. Further than this, comparisons were made with an analysis done by the present authors. There seems to be consistency within the sources in the use of the terms total loss, casualty and accident/incident. The rates were observed to decrease by an order of magnitude going from accident/incident to casualty and likewise from casualty to total loss. The overall frequencies were found to be in the range of 0·0009 to 0·07 total losses per 106 ship miles, 0·03 to 1 casualties per 106 ship miles, and 0·5 to 13 accidents/incidents per 106 ship miles. It was found that the frequency depends on visibility, brightness, geographical environment, age of vessel and size of vessel. Collision and grounding frequencies were found to increase with decreasing visibility, brightness and more restricted waters. Collision frequencies were found to increase with increasing size of vessel. Fire/explosion and structural damage frequencies were found to increase with increasing age, and collisions to decrease with increasing age. No firm trend was found from the effect of flag state or type of vessel.

As Satellite Clock Bias (SCB) prediction may be affected by various factors such as periodic items, sampling length, and stochastic items, a fusion-based prediction method is proposed by considering characteristics of SCB and fitted residue. On this basis, an instance algorithm is presented by fusing four typical prediction models. First, we use Empirical Mode Decomposition (EMD) to pre-process and decompose the SCB series into multiple components with various characteristics. Then, we analyse the fitting performance of each model for different components and prediction length, namely short-, mid- and long-term prediction, and select models with the best performance. Next, we analyse fitted residue of the reconstructed SCB, and select the model with the best fitting results. Finally, we fuse the multiple selected models for SCB prediction. The method is tested using Global Positioning System (GPS) precise clock products provided by the International Global Navigation Satellite System Service (IGS). Experimental results show that, compared with single prediction models and existing combination models, the proposed fusion-based prediction method improves accuracy and stability. In particular, the proposed method is more stable and has better performance for mid- and long-term prediction.

This article presents research on how frequently seafarers utilise functions and information available on an Integrated Navigation System to perform navigation duties. Using an online questionnaire, the study collected data from 601 members of the global seafaring community. The results provide an overview of the frequency of use for each feature, together with factors affecting the use and associated usability issues. The study finds that the use of navigation equipment is situation-dependent and affected by administrative factors, experience and professional habits, characteristics of the sailing area, traffic conditions, weather conditions, ship management factors and geographical location. Additionally, information overload, particularly with overlay and alert management functions, was found to be the major issue with existing systems. The findings of this study can be applied to improve menu tree structure, display layout, and interaction methods on the interface of navigation systems, such as making frequently-used features more readily available or easier to access.

In nature, science and engineering, we often come across helicoidal surfaces. A curve on a helicoidal surface in Euclidean 3-space is called a loxodrome if the curve intersects all meridians at a constant azimuth angle. Thus loxodromes are important in navigation. In this paper, we find the differential equation of the loxodrome on a helicoidal surface in Euclidean 3-space. Also we give some examples and draw the corresponding pictures via the Mathematica computer program to aid understanding of the mathematics of navigation.

The civilian Automatic Identification System (AIS) has no inherent protection against spoofing. Spoofed AIS messages have the potential to interfere with the safe navigation of a vessel by, amongst other approaches, spoofing maritime virtual aids to navigation and/or differential global navigation satellite system (DGNSS) correction data conveyed across it. Acting maliciously, a single transmitter may spoof thousands of AIS messages per minute with the potential to cause considerable nuisance; compromising information provided by AIS intended to enhance the mariner's situational awareness. This work describes an approach to authenticate AIS messages using public key cryptography (PKC) and thus provide unequivocal evidence that AIS messages originate from genuine sources and so can be trusted. Improvements to the proposed AIS authentication scheme are identified which address a security weakness and help avoid false positives to spoofing caused by changes to message syntax. A channel loading investigation concludes that sufficient bandwidth is available to routinely authenticate all AIS messages whilst retaining backwards compatibility by carrying PKC ‘digital signatures’ in a separate VHF Data Exchange System (VDES) side channel.

Civil and military unmanned aircraft systems (UAS) operations are currently subject to restrictions that put major limits on their use of airspace. There is considerable debate about how to develop the safe, secure and efficient integration of UAS into non-segregated airspace and aerodromes. This paper examines a necessary safety aspect. Airlines and their passengers would obviously ask, “Is it still safe with all these unmanned aircraft around?” The spotlight must be on Air Traffic Control Systems as High Reliability Organizations (HRO). That status comes from industry characteristics: focus on safety, effective use of technological improvements, learning from feedback from accidents/incidents, and an underpinning safety culture. The safety of ATC Systems has improved dramatically: accidents are now the product of rare and complex ‘messes’ of multiple failures. It is therefore a major challenge to preserve the HRO status by ensuring at least current safety performance. The analysis sketches feasible processes of policy decision-making and safety analyses. Key factors are policies on UAS equipage and airspace usage, implementation of a Traffic Alert and Collision Avoidance System (TCAS)-variant appropriate for UAS, use of an ‘Equivalent Level of Safety’ philosophy, small datalink latencies, proven HRO safety and learning cultures, and stress testing of system resilience by real-time simulations.

The main problem in polar navigation is one of direction, and the problem has two facets. First we have to measure direction and then we have to describe it. Generally, the seaman has a gyro-compass by which he can measure the heading of his ship. As you know, the gyro-compass is simply a gyro which keeps pointing towards the pole. If we have a gyro close to the north pole and pointing north, it will continue to point in the same direction however the ship turns beneath it. So also will it continue to point in the same direction if the Earth turns beneath it. In twelve hours it will be pointing south instead of north.

The chief failing of surface astronavigation in its traditional form is reliability – it needs clear skies! Any solution to this limitation must therefore centre on a more weather-independent means of both detecting and identifying astronomical objects. This implies that the detection process should be conducted not in the optical but in the radio waveband, although radio astronomy makes it clear that the rather simple distribution and ‘point’-like images seen visually do not exist at radio wavelengths.

A review of safety targets for en route ATC radar separation suggests that the existing target level of safety (TLS) is over-cautious. If risk budgeting principles are followed consistently, a ‘radar TLS’ of 1·0×10−9 fatal aircraft accidents per flying hour is appropriate. This rate is consistent with Joint Aviation Authorities (JAA) guidance on system failure conditions leading to catastrophic accidents. Dynamic and static calculations using published data are compared. The new methodology shows where there are problems with the traditional static calculations, and how to improve the estimation. A further improvement introduces a simple robust model of the controller's decision processes. The focus is not on describing what controllers would generally do, but on setting criteria based on what they could not reasonably be expected to do. This additional ingredient into the calculation adds realism and ensures that attention is focused on hazardous correlated errors. Focused data collection would be an essential component of new risk estimates. The key information required would be on radar performance and the nature and frequency of use of radar separation, including the relative velocities for proximate events at closest point of approach and the frequency of correlated gross errors (through a conditional probability factor). If this factor is not properly taken into account, then the data collection and analysis could be inefficient.

This paper presents a practical application of the probabilistic-fuzzy method for assessment of the safety of a ship manoeuvring in waterways. The method, based on probabilistic risk analysis and elements of fuzzy logic, takes into account situations of threatened navigational safety and situations when a navigator intuitively thinks that the safety of manoeuvring ship is threatened. The probability of grounding a ship manoeuvring in a waterway bend is determined by means of simulation method. Then, with the use of experts' knowledge and tools of fuzzy logic the probability of a dangerous situation is determined. Two different approaches are applied for the determination of that probability. The results are compared.