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.

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.

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.

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.

Vector tracking of global navigation satellite systems (GNSS) signals and deeply integrating GNSS with an inertial navigation system (INS) improve robustness and accuracy in poor GNSS signal-to-noise environments. Both require a dedicated interface between the GNSS receiver and the navigation processor to enable the GNSS receiver to output the correlator measurements and input numerically-controlled oscillator (NCO) commands. This paper investigates the requirements for such an interface. Data latency is analysed for a range of different stand-alone GNSS vector tracking and deep INS/GNSS integration architectures. Suitable latency compensation techniques are identified. It is shown that, for the majority of applications, an NCO command update rate of 50 Hz with latency compensation and 100 Hz without is sufficient. An approach to interface standardisation which can handle a wide range of different GNSS signals and receiver designs is proposed.

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.

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.

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.

Acquisition of unaided weak Global Positioning System (GPS) signals requires long coherent integration time and thus all the possible navigation data bit combination paths have to be searched. In this paper, to improve the computational efficiency, the Improved Fast Modified Double-Block Zero Padding (IFMDBZP) algorithm using the Optimal Path Search Method (OPSM) is proposed instead of the FMDBZP algorithm using the All Paths Search Method (APSM). The proposed method consists of unlikely data bit combination path elimination by applying the Viterbi algorithm during each coherent integration step to improve the FMDBZP algorithm. The analyses show that the proposed OPSM can reduce the computation calculations and save memory space without suffering any loss compared to the APSM. And the longer the coherent integration time is, the more benefit one can gain from the proposed method. The simulation results also show that the IFMDPZP algorithm using the proposed OPSM has the same acquisition performance as the APSM.

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.

This paper reports the results of the first three in a series of experiments on tactile perception which form part of a larger project on tactile perceptions and spatial representations and the design of tactile interfaces for mobility devices for blind, partially sighted and deafblind people. The results indicate the potential of tactile interfaces, including to support environmental exploration and mobility. The participants showed reasonably good ability to determine the direction of motion of an arrow, with best recognition rates in the up and right directions. They showed reasonably good ability to use a tactile interface to detect and avoid obstacles after a very short learning period and more limited ability to learn and remember an environmental representation using information from a tactile interface and walking through the environment without specific instructions.

This paper presents the results of a research project that investigated the potential benefits of a combined Galileo/GPS navigation system. The research addressed in detail the two key required navigation performance (RNP) parameters of accuracy and integrity. The project was supported by Alcatel Space and was a contribution to the Galileo definition studies (supported by the European Community under the GALA project). The results show significant improvements in both accuracy and integrity (achievable through RAIM) when a combined constellation is used rather than Galileo alone.

The possibility of identifying the type of multipath environment and receiver motion (e.g. pedestrian, vehicular) using pattern recognition approaches based on multipath parameters is investigated. This allows the receiver to adjust its tracking strategy and optimally tune its tracking parameters to mitigate code multipath effects. A Support Vector Machine (SVM) classification method with a modified Gaussian kernel is applied in this approach. A set of temporal and spectral features is extracted from the correlation samples of the received signals in different environments to train the classifier. The latter is then used in the structure of stochastic gradient-based adaptive multipath compensation and tracking techniques to tune the signal tracking parameters based on the environment and receiver motion. Simulation and real data measurements using Galileo E1B/C signals are performed to assess the validity of the proposed environment identification approaches and to evaluate the impact of the proposed context-based receiver parameter tuning techniques on tracking performance in multipath environments. Test results showed that the proposed classifiers have an accuracy between 86% and 92%, and the tracking performance improved by about 15%.

This is the first of two papers on Quantitative Safety Assessment – vital to the successful introduction of future Air Traffic Management systems. The goal of the two papers is to identify key future questions and the best methods to deal with them. The focus is en route European commercial traffic in controlled airspace, particularly risks from mid-air collision. Part 1 is a critical sketch of the historical context, methods used, and the use of analytical ‘models’ for safety assessment. Aspects covered include safety philosophy principles, safety targets, procedural separation standards, the Reich model and its problems, and radar separation standards.

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 aim of the SPACE project is to develop a mobile test bed that can position to within centimetres in all conditions and environments. To achieve this goal, a number of different positioning technologies have to be integrated together including GNSS, INS, pseudolites and other technologies such as Ultra Wideband and Bluetooth ranging. The integration of these sensors is achieved by the development of a ‘plug and play’ filter that will optimally combine measurements from each sensor to form an accurate position solution. The filter has been designed so that the sensors are integrated at the measurement level wherever possible, so partial measurements from different systems can be used together.

This paper describes the development of the plug and play filter, focussing in particular on how the states are defined, how the measurements are used, and how a generic filter can be developed that can integrate all types of positioning sensor. Some early results from the filter are shown integrating GPS, INS and simulated measurements from an Ultra Wideband system. A prototype version of the mobile test bed is also described.

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 new unambiguous tracking technique based on combined correlation functions for sine Binary Offset Carrier (BOC) signals is proposed in this paper. The key to this method is to exploit two types of local reference signals: the BOC signal and a linear combination of a series of BOC signals with different delays. They are both correlated with the received signals. Then, a correlation function without any positive side peaks is obtained by multiplying the two correlation results to make tracking completely unambiguous. Theoretical analysis and simulation in the tracking stage show that the proposed method has the best code tracking accuracy among the method tracking BOC signals like Binary Phase-Shift Keying signals (BPSK-LIKE), the Pseudo correlation function based Unambiguous Delay Lock Loop (PUDLL), Symmetrical Pulse Ambiguity Removing (SPAR) technique, the method proposed by Shen Feng (SF) and the two methods proposed by Yan Tao (YT-V1 and YT-V2). In multipath environments, the proposed method has the best anti-multipath performance of all the tracking methods mentioned above. In conclusion, the proposed method can completely eliminate ambiguity and has significant performance advantages compared with the methods mentioned above.

The roll motion of a ship on waves is one of the six degrees of freedom and is the most difficult to predict since it deals with a motion similar to a spring-mass damper system, poorly damped by ship generated waves, in addition to the action of waves from the high seas. This problem increased from the second half of the 19th century when sailing propulsion was replaced by steam machines and iron replaced wood, which led to design modifications in ships affecting transversal stability, with the result of an increment in the ship's roll motion. As a consequence, it has been necessary to develop different systems which, on the one hand, increase the natural period of this motion in order to decrease its amplitude and reduce the risks that the wave encounter frequency would resonate with the natural frequency of the ship's motion; and on the other hand, to generate a damping effect to this motion. Bilge keels, passive stabilisers with no moving parts, form the simplest and cheapest element that may be incorporated on a ship to reduce this motion. This paper studies roll motion in general and then analyses bilge keels from different points of view.

The new millennium brought an asymptotic interest in space technology. Besides existing operational global positioning systems i.e. GPS and GLONASS, another two have already emerged: GALILEO and Compass/Beidou. Alternatives to GPS imposed the GNSS concept, which has crystallized in a short time. The true reasoning of this excessive need for positioning information is beyond the scope of this paper; instead, an analysis of orbital behaviour of GPS, GLONASS and GALILEO is conducted. GNSS orbits have similar characteristics permitting us to encompass them under the term Medium Earth Orbits (MEO). However, small differences between mean orbital elements of the three systems produce a significantly different reaction of their satellites' orbits to the natural perturbing factors. This study analyzes the three space segment characteristics, introduces the analytical method used to evaluate variations of orbital elements under the most significant perturbing influences and offers a broad comparative image of the dynamic behaviour of the three GNSS constellations.