The importance of the Global Positioning System (GPS) and related electronic systems continues to increase in a range of environmental, engineering and navigation applications. However, civilian GPS signals are vulnerable to Radio Frequency (RF) interference. Spoofing is an intentional intervention that aims to force a GPS receiver to acquire and track invalid navigation data. Analysis of spoofing and authentic signal patterns represents the differences as phase, energy and imaginary components of the signal. In this paper, early-late phase, delta, and signal level as the three main features are extracted from the correlation output of the tracking loop. Using these features, spoofing detection can be performed by exploiting conventional machine learning algorithms such as K-Nearest Neighbourhood (KNN) and naive Bayesian classifier. A Neural Network (NN) as a learning machine is a modern computational method for collecting the required knowledge and predicting the output values in complicated systems. This paper presents a new approach for GPS spoofing detection based on multi-layer NN whose inputs are indices of features. Simulation results on a software GPS receiver showed adequate detection accuracy was obtained from NN with a short detection time.

The earlier papers in this series described the principles, and some of the techniques, which determine the approach to separation standards made at the Royal Aircraft Establishment. In this approach to the problems of estimating safe separation standards and specifying the quality of navigation needed, emphasis is laid on the observations of flying errors which occur in operational conditions. Dependence on theoretical assumptions is limited to the extent necessary to make usable ‘upper limit’ estimates of collision risk. Where critical assumptions are unavoidable, their nature and effects are shown.

AIS was primarily developed to exchange vessel-related data among vessels or AIS stations by using very-high frequency (VHF) technology to increase safety at sea. This study evaluates the formal integrity, availability, and the reporting intervals of AIS data with a focus on vessel movement prediction. In contrast to former studies, this study is based on a large data collection of over 85 million AIS messages, which were continuously received within a time period of two months. Thus, the evaluated data represent a comprehensive and up-to-date view of the current usage of AIS systems installed on vessels. Results of previous studies concerning the availability of AIS data are confirmed and extended. New aspects such as reporting intervals are additionally evaluated. Received messages are stored in a database, which allows for performing database queries to evaluate the obtained data in an automatic way. This study shows that almost ten years after becoming mandatory for professional operating vessels, AIS still lacks availability for both static and dynamic data and that the reporting intervals are not as reliable as specified within the technical AIS standard.

The ship domain is a very important and useful concept in marine traffic engineering. It has been widely used in traffic simulation models, for encounter criteria, traffic lane design criteria, VTS planning, risk assessment, collision avoidance, and for other applications.

Dr Y. Fujii, Dr E. M. Goodwin and Dr T. G. Coldwell have done a lot of work on this subject. The differences between their ship domain concepts are described in the second part of this paper. In the third part, the authors have used a new branch of social psychology – the theory of Proxemics – to analyse the factors which affect the ship domain, and point out that the basis of producing ship domains is in the field of Proxemics. Finally, in the fourth part of this paper, some problems in ship domains are analysed.

The paper introduces a new method of solving multi-ship encounter situations for both open waters and restricted water regions. The method, called evolutionary sets of safe trajectories, combines some of the assumptions of game theory with evolutionary programming and aims to find optimal sets of safe trajectories of all ships involved in an encounter situation. In a two-ship encounter situation it enables the operator of an onboard collision-avoidance system to predict the most probable behaviour of a target and to plan the own manoeuvres in advance. In a multi-ship encounter the method may be used to help an operator of a VTS system to coordinate the manoeuvres of all ships. The paper contains a detailed description of collision-avoidance operators used by the evolutionary method and simulation examples of the method's results for digital maps.

A marine traffic accident may be defined in the wider sense as a collision or stranding and in a narrow sense as a collision. Several reports are available on the causes of collisions and on the relation of collision frequency to such factors as location, weather and time; S. Fujii continuing Asai's work has shown that the ratio, R, between the number of vessels in collision and the number of vessels registered increases with the length of the vessel between perpendiculars. Shiobara gives a linear correlation between log R and log G with a slope of 0·5 and a correlation factor of 0·95, where G is the gross tonnage. In other words the collision frequency is proportional to L1.4. He further shows that R is almost proportional to L.

Satellite velocity determination using the broadcast ephemeris is discussed and it is pointed out that the conventional rotation matrix method involves a complicated process of computation. This paper proposes an alternative method using a simple differentiator to derive satellite Earth-Centred-Earth-Fixed (ECEF) velocity from the ECEF satellite positions that are calculated using the standard ICD-GPS-200 algorithm. The proposed algorithm simplifies the velocity transformation procedure, and therefore provides a good alternative. It is demonstrated that ±1 mm/s per axis ECEF satellite velocity is achievable by using the first-order central difference of a Taylor series approximation.

A closed-form formula is also derived for the determination of GPS satellite ECEF acceleration using the broadcast ephemeris. This formula is capable of accuracies better than ±0·1 mm per second squared in each axis. With such a high accuracy of satellite acceleration in real-time, it is possible to detect the line-of-sight range acceleration precisely and as such it is concluded that a GPS receiver can be considered as a precise accelerometer.

The success of the position differential method implies that real-time satellite ECEF velocities can be directly derived through numerical differentiation of the position polynomials. This is desirable for GPS velocity determination applications which require high output rate results in real-time. The derived closed-form formula for GPS satellite ECEF acceleration would benefit those who attempt to use a GPS receiver as an accurate accelerometer in real-time.

The Strait of Istanbul which constitutes one of the major and busiest seaways in the world links the Black Sea to the Sea of Marmara, it is a narrow “S-shaped” channel, open day and night for international shipping. Currents and darkness are the two dominant factors causing marine casualties in the Bosphorus. In this regard, Yenikoy and Umuryeri (or Umur Banki) are the two critical areas where most of the stranding and grounding casualties occur as vessels negotiate sharp turns (80° at Yenikoy, 70° at Umuryeri). The casualty case investigations reveal that in most of the incidents, vessels lose their manoeuvrability in the course of taking a sharp turn with the current. The number of casualties occurring in darkness was found to be nearly twice the number of occurring in daylight. A total of 461 marine casualties of different types occurred in this tricky strip of water during the period 1953–2002, the majority being collisions. Since 1994 when the TSS was introduced there have been 82 marine casualties the majority of which have been groundings/strandings.

This paper examines marine casualties in-depth in relation to casualty types, numbers of ships, the localities where most incidents occur, and external factors such as currents and darkness that contribute to marine casualties in the Strait. The major factors are deduced in order to suggest possible solutions.

This paper presents a concept on the subjective ship domain. The factors related to the domain are discussed. A method based on the neural networks is used to establish a model of the domain that considers the effects of visibility and manoeuvrability, which can react quickly to various ships within a certain range.

The article introduces a method of finding optimal routes on raster planes. The method presented takes advantage of a new algorithm that tends to minimize a number of direction changes within a route, while steering clear of the obstacles. Two different schemes, suitable for restricted area Vessel Traffic Service (VTS) system and collision avoidance system located on the own ship are described. The VTS-oriented scheme supports VTS priority policy that may extend or override international give-way regulations. The own-ship routing scheme in a give-way situation is capable of determining the shortest safe path to the destination point. The method takes into account own ship dynamics. It has linear time and space complexities and therefore is sufficiently fast to perform real-time routing on the raster grids. Both the general method and the algorithm it uses are presented in detail in the paper. Implementation issues are also discussed.

The integration of Global Positioning Systems (GPS) with Inertial Navigation Systems (INS) has been very actively studied and widely applied for many years. Some sensors and artificial intelligence methods have been applied to handle GPS outages in GPS/INS integrated navigation. However, the integrated system using the above method still results in seriously degraded navigation solutions over long GPS outages. To deal with the problem, this paper presents a GPS/INS/odometer integrated system using a fuzzy neural network (FNN) for land vehicle navigation applications. Provided that the measurement type of GPS and odometer is the same, the topology of a FNN used in a GPS/INS/odometer integrated system is constructed. The information from GPS, odometer and IMU is input into a FNN system for network training during signal availability, while the FNN model receives the observations from IMU and odometer to generate odometer velocity correction to enhance resolution accuracy over long GPS outages. An actual experiment was performed to validate the new algorithm. The results indicate that the proposed method can improve the position, velocity and attitude accuracy of the integrated system, especially the position parameters, over long GPS outages.

Extensive ionospheric scintillation and Total Electron Content (TEC) data were collected by the Institute of Engineering Surveying and Space Geodesy (IESSG) in Northern Europe during years of great impact of the solar maximum on GNSS users (2001–2003). The ionospheric TEC is responsible for range errors due to its time delay effect on transionospheric signals. Electron density irregularities in the ionosphere, occurring frequently during these years, are responsible for (phase and amplitude) fluctuations on GNSS signals, known as ionospheric scintillation. Since June 2001 four GPS Ionospheric Scintillation and TEC Monitor receivers (the NovAtel/AJ Systems GSV4004) have been deployed at stations in the UK and Norway, forming a Northern European network, covering geographic latitudes from 53° to 70° N approximately. These receivers compute and record GPS phase and amplitude scintillation parameters, as well as TEC and TEC variations. The project involved setting up the network and developing automated archiving and data analysis strategies, aiming to study the impact of scintillation on DGPS and EGNOS users, and on different GPS receiver technologies. In order to characterise scintillation and TEC variations over Northern Europe, as well as investigate correlation with geomagnetic activity, long-term statistical analyses were also produced. This paper summarises our findings, providing an overview of the potential implications of ionospheric scintillation for the GNSS user in Northern Europe.

A review of the nuclear magnetic resonance gyroscope (NMRG) as a rotation-rate sensor is presented. Most of the activity in the recent past on NMRG research originated in the USA and concentrated almost exclusively on forms of the NMRG utilizing optical-pumping techniques. To date, only the National Air Defence Centre at Warminster, Pennsylvania continues to pursue a low-cost variant of the NMRG while in the UK, only ARE (Slough) and Sussex University remain active in NMRG research. The emphasis on activity in the Navigation Division at ARE (Slough) has continued to be on cryogenic helium-3 (3He) techniques and the use of superconducting shielding (although optical-pumping will also be pursued). The continuing incentive for NMRG research remains the requirement for a ship's low-cost inertial navigation system (SLINS).

GPS is the most widely used global navigation satellite system. By design, there is no provision for real time integrity information within the Standard Positioning Service (SPS). However, in safety critical sectors like aviation, stringent integrity performance requirements must be met. This can be achieved externally or at the receiver level through receiver autonomous integrity monitoring (RAIM). The latter is a cost effective method that relies on data consistency, and therefore requires redundant measurements. An external aid to provide this redundancy can be in the form of an Inertial Navigation System (INS). This should enable continued performance even during RAIM holes (when no redundant satellite measurements are available). However, due to the inclusion of an additional system and the coupling mechanism, integrity issues become more challenging. To develop an effective integrity monitoring capability, a good understanding of the potential failure modes of the integrated system is vital. In this paper potential failure modes of integrated GPS/INS systems are identified. This is followed by the specification of corresponding models that would be required to investigate the capability of existing integrity algorithms and to develop enhancements or new algorithms.

In general, a Reference Station calculates differential corrections which are valid for that exact location (zero baseline) at that particular epoch (age of corrections zero). However, DGPS users may be located as far as 200 nm away from the Reference Station and some of the errors compensated for by the Reference Station vary with space, namely satellite ephemeris, tropospheric and ionospheric errors. Therefore, the corrections calculated at the Reference Station suffer certain accuracy degradation as the separation distance increases, because of a decreasing relevance of the Reference Station data to the user. The error growth with increasing distance to the beacon is accentuated by the inability of Reference Station and user to see the same satellites, commonly termed the lack of intervisibility. The error growth with distance is the most important factor determining DGPS accuracy, but surprisingly very little has been done to assess it. US official documents and IALA state that the achievable accuracy degrades at an approximate rate of 1 m for each 150 km (80 nm) distance from the broadcast site, but this value is based on a theoretical prediction, made back in 1993. To estimate the error growth with real data, 6 DGPS receivers were placed along the Portuguese coastline at approximately 50 nm intervals from Sagres Broadcast Station, in a South – North direction. This paper describes the results of the trial.

A magnetic compass has too large a heading error for many applications, and it is often not obvious how to achieve an accurate heading, in particular for low-cost navigation systems. However, there are several different methods available for finding heading, and their feasibility depends on the given scenario. Some of the methods may seem very different, but they can all be related and categorised into a list by studying the vector that each method is using when achieving heading. A list of possible methods is very useful when ensuring that all relevant methods are being considered for a given application. For practical navigation, we have identified seven different vectors in use for heading estimation, and we define seven corresponding methods. The methods are magnetic and gyrocompass, two methods based on observations, multi-antenna Global Navigation Satellite Systems (GNSS), and two methods based on vehicle motion.

Fujii shows that the collision diameter is about 1/10,000 of the ship length; this figure is to be interpreted as meaning that skilful manœuvres decrease the collision frequency to about 1/10,000 and, since the geometrical collision diameter is of the same order as the ship length L, attention has to be paid to ‘collisions’ which include even slight contact. The probability of a mismanœuvre which leads to stranding is studied using the marine traffic accident ‘library’ of the Japanese Association for Preventing Sea Casualties and the Report on the Marine Traffic Survey of the same Association. The library includes records of casualties in the original cards both of Marine Casualty Statistics and Statistics of Marine Accidents Requiring Rescue. The authors were members of the working group which prepared both the library and the Report. In this paper stranding includes any kind of grounding unless intentional, e.g. after collision or fire, and includes groundings with slight damage such as bottom contact.

A scrutiny of the existing time differencing carrier phase (TDCP) velocity estimation algorithms has revealed several shortcomings that could be further improved. One of these is that the velocity estimation at epoch t would require the receiver positions at epoch t+Δt or more are available. Another is the usage of satellite velocities in the calculations which would increase the receiver computational load and degrade the accuracy. In this paper, an improved TDCP velocity estimation approach has been proposed and tested. The new approach depends only on receiver position at epoch t and satellite positions at epoch t and t+Δt. Satellite velocities are not required in this calculation. This proposed algorithm has been validated using static and kinematic field test data, showing that equivalent velocity accuracy achievable by using differential GPS techniques can be made possible with the proposed standalone GPS method.

It is important for maritime authorities to effectively classify and identify unknown types of ships in historical trajectory data. This paper uses a logistic regression model to construct a ship classifier by utilising the features extracted from ship trajectories. First of all, three basic movement patterns are proposed according to ship sailing characteristics, with related sub-trajectory partitioning algorithms. Subsequently, three categories of trajectory features with their extraction methods are presented. Finally, a case study on building a model for classifying fishing boats and cargo ships based on real Automatic Identification System (AIS) data is given. Experimental results indicate that the proposed classification method can meet the needs of recognising uncertain types of targets in historical trajectory data, laying a foundation for further research on camouflaged ship identification, behaviour pattern mining, outlier behaviour detection and other applications.

The aviation community has very stringent navigation integrity requirements that apply to a variety of manned and Unmanned Aerial Vehicle (UAV) operational tasks. This paper presents the results of the research activities carried out by the Italian Air Force Flight Test Centre (CSV-RSV) in collaboration with the Nottingham Geospatial Institute (NGI) and Cranfield University (CU) in the area of Avionics-Based Integrity Augmentation (ABIA) for mission- and safety-critical Global Navigation Satellite System (GNSS) applications. Based on these activities, suitable models were developed to describe the main causes of GNSS signal outage and degradation in flight, namely: antenna obscuration, multipath, fading due to adverse geometry and Doppler shift. Adopting these models in association with suitable integrity thresholds and guidance algorithms, the ABIA system delivers integrity caution (predictive) and warning (reactive) flags, as well as steering information to the pilot and electronic commands to the aircraft/UAV flight control system. These features allow real-time avoidance of safety-critical flight conditions and fast recovery of the required navigation performance in case of GNSS data losses. This paper presents the key ABIA concepts, architecture and mathematical models. A successive paper will address the ABIA integrity thresholds criteria and detailed results of a TORNADO simulation case-study.