A spoofing attack on a global navigation satellite system (GNSS) receiver is a threat to a significant community of GNSS users due to the high stakes involved. This paper investigates the use of slope based metrics for the detection of spoofing. The formulation of slope based metrics involves monitoring correlators along with tracking correlators in the receiver's channel, which are slaved to the prompt tracking correlator. In this study, using some candidate metrics, detectors have been formed through the analysis of simulated spoofing attacks. A theoretical variance of each metric has also been calculated as a reference for the threshold. A threshold is estimated using the measured variance from the clean signals, for specific false alarm rate. By using the measured threshold, detectors are formed based on slope metrics. These detectors have been tested using TEXBAT data. The results show that the differential slope metrics have good performance. The results have also been compared with some other techniques of spoofing detection.

In this paper, a conventional Strapdown Inertial Navigation System (SINS) alignment method on a disturbed base is analysed. A novel method with an attitude tracking idea is proposed for the rocking base alignment. It is considered in this method that the alignment algorithm should track the rocking base attitude real changes in the alignment process, but not excessively restrain disturbance. According to this idea, a rapid alignment algorithm is devised for the rocking base. In the algorithm, coarse alignment is carried out within 30 s in the inertial frame with alignment precision less than 2°, which meets Kalman filter linearization conditions well. Then a Kalman filter with ten state vectors and four measurement vectors is applied for the fine alignment to improve the capability of the algorithm in tracking the vehicle attitude. A turntable rotation experiment is carried out to validate the capability of the fine algorithm in tracing the large magnitude change during alignment. It is shown that the repeated alignment precision is about 0·04° by the alignment experiment on a rocking vehicle, with alignment time of 180 s. The Laser Strapdown Inertial Navigation System (LINS) ground navigation experiment suggests that the algorithm proposed by this paper can be satisfied without the need of high precision SINS alignment.

Navigation and positioning system users are demanding greater accuracy and reliability in ever more challenging environments. This is driving a wave of rapid innovation, with the result that multisensor integrated navigation systems will become much more complex. This introduces a number of problems, including how to find the necessary expertise to integrate a diverse range of technologies, how to combine technologies from different organisations that wish to protect their intellectual property, and how to incorporate new navigation technologies and methods without having to redesign the whole system. It also makes it desirable to share development effort over a range of different applications. To address this, the feasibility of a modular approach to the design and development of multisensor integrated navigation and positioning systems is analysed. Assessments of the requirements of different user communities and the adaptability of the different navigation and positioning technologies to different contexts and requirements are presented. Based on this, the adoption of an open interface standard for modular integration is recommended and the issues to be resolved in developing that standard are outlined.

The Japanese Quasi-Zenith Satellite System (QZSS) is a regional satellite navigation system capable of transmitting navigation signals that are compatible and interoperable with other Global Navigation Satellite Systems (GNSS). In addition to navigation signals, QZSS also transmits augmentation signals, e.g. the L-band Experimental (LEX) signal. The LEX signal is unique for QZSS in delivering correction messages such as orbits and clock information that enable real-time Precise Point Positioning (PPP). This study aims to evaluate the availability of the LEX signal as well as the quality of the broadcast correction messages for real-time PPP applications. The system is tested in both static and kinematic positioning modes. The results show that the availability of the LEX signal is 60% when the QZSS satellite elevation is at 30° and above 90% when the satellite is above 40° elevation. Centimetre-level position accuracy can be obtained for static PPP processing after two hours of convergence using the current MADOCA-LEX (Multi-GNSS Advanced Demonstration of Orbit and Clock Analysis) correction messages transmitted on the LEX signal; and decimetre-level point positioning accuracy can be obtained for kinematic PPP processing.

In September 1931 Sir Hubert Wilkins and Harald Sverdrup made the first attempt to explore the Arctic Ocean by submarine in Wilkins's Nautilus. The Nautilus was the ex-Navy submarine O-12 modified with topside runners to slide against the underside of the sea ice. Seventeen years later the US Navy developed the sonar system necessary for safely piloting a diesel-battery submarine underneath the ice pack and began exploration of ice covered areas.

In 1957, with the nuclear-powered Nautilus, the US Navy began exploration far into the Arctic Ocean. Problems were found concerning determination of ship's position, ice avoidance manoeuvres, and surfacing up through ice. Sonar and inertial navigation equipments and operating techniques were developed to solve these problems. Submarines have since sailed to all parts of the Arctic Ocean during all seasons — more than twenty explorations since 1957. The history, problems and interrelationships of the many explorations are described.

Dr Lyon's paper was presented at a colloquium on the conquest of the North Pole held in Paris, 7–1 1 November 1983, and organized by the Centre d'Etudes Arctiques by whose permission it is here published. (Throughout the paper miles means nautical miles.)

This paper investigates the thermal characteristics of typical Micro Electro-Mechanical System (MEMS) Inertial Measurement Units (IMUs) with a reliable thermal test procedure. Test results show that MEMS sensor errors, not only biases, but also scale factors and non-orthogonalities, may vary significantly with temperature. Also, MEMS sensor errors can have significant inconsistent curves under different temperature changing profiles. The existence of such inconsistencies posed a challenge to the following assumption of thermal calibration: the thermal drift of a sensor error is only related to the temperature of the sensor core. A robust way to mitigate this issue is given by using the sensor data during both heat-and-stay and cool-and-stay processes to establish the final thermal models. The performance of both IMUs and inertial navigation systems improved significantly after compensation with the established thermal models. Additionally, the variation of the IMU thermal parameters with time was observed, which suggests that periodical thermal calibration is necessary for MEMS IMUs.

International discussions on the concept of e-navigation have identified a robust position-fixing system as one of the essential components. Global Navigation Satellite Systems (GNSS) are known to have vulnerabilities and onboard alternatives such as inertial systems have limitations. This paper considers the case for an enhanced version of the terrestrial radio-navigation system Loran to provide an alternative with performance comparable to GNSS. The paper reviews recent studies of inertial navigation systems and concludes that they do not present a fully capable backup to GNSS at present. Trials of enhanced Loran carried out in the UK by the General Lighthouse Authorities have shown that eLoran does have the potential to provide equivalent performance to GNSS over long periods and is a fully complementary system. The steps needed to provide eLoran on at least a regional basis, covering critical waterways, are considered. The international process for the specification and standardisation of eLoran is already underway and some projections are made about the timescale for full implementation, in the context of the introduction of e-Navigation. A version of this paper was first presented at NAV 07 held in Church House, London from 30th October – 1st November 2007.

Marine accident analysis is important for ships passing through narrow, shallow and busy waterways. This study analyses the accidents which have occurred in the Istanbul Strait and proposes both quantitative and qualitative assessments of marine accidents. Marine accidents occurring in the Istanbul Strait are analysed by using a method based on neuro-fuzzy and genetically optimised fuzzy classifiers. It can be concluded that accident severity increases when poor weather conditions prevail in the Strait regardless of ship size. Therefore, solutions to reduce unwanted events should be prioritised by accounting for weather conditions and the capacity of the vessels. This analysis indicates that the safety level would be significantly improved if all the vessels follow the passage guidelines.

This paper outlines the design of a Vessel Traffic Management and Information System (VTMIS) for the Turkish Straits and taking this as an example shows how modelling and simulation may aid safe and efficient navigation of vessels through waterways which are narrow and winding with changing currents and are therefore difficult to navigate and prone to accidents. Ship Handling and Vessel Traffic Flow simulation models and Hyrographic Prediction model are described and the simulation trials conducted under different traffic and environment conditions are discussed to show the role that these prediction and simulation programmes can play in preventing marine casualities in different waterways, which may result in loss of human lifes and property and contamination of the environment.

This paper optimises two-ship collision-avoidance manoeuvres accounting for both collision risk and fuel use. A collision-avoidance manoeuvring optimisation model is developed to minimise fuel consumption while assuring ships' operational safety. The model can optimally determine when to begin collision-avoidance actions, how to change courses, and what rudder angles are needed. A quantitative scenario simulation is developed to illustrate the model application. The methodology can be further developed to guide practical ship collision-avoidance manoeuvring decisions made under more operational scenarios. In particular, this research can contribute to the development of computer-aided collision-avoidance operations to improve the safety and energy efficiency of maritime transportation.

The Global Positioning System (GPS) is now attracting worldwide attention as a navigation sensor. One of the advantages of GPS is that people can find their position using a GPS receiver wherever they are except in obstructed environments. Existing GPS receivers do not work in an obstructed environment despite there being many potential applications. This paper shows the possibility of navigation using GPS technologies indoors in a blocked environment. The paper describes the pseudolite-based indoor navigation system that was developed and implemented at Seoul National University (SNU). The system, which uses GPS technologies, has some different characteristics to normal outdoor GPS systems. The differences cause some practical problems, such as near/far, time-tag, multipath and unknown transmission position problems, which need to be solved to implement the indoor navigation system. The paper introduces various methods for solving such problems. The paper then shows the experimental results and the system accuracy. The satisfactory experimental results show that the RMS static error is 1 mm(1σ) horizontally and 2 mm(1σ) vertically and the RMS dynamic error is 5·6 mm(1σ) horizontally and 15 mm(1σ) vertically. The paper also shows the result of a field application test in the ocean engineering basin of the Korea Research Institute of Ships & Ocean Engineering (KRISO).

Autonomous orbit determination of a navigation constellation is the process by which the orbit parameters of navigation satellites are autonomously calibrated onboard the satellites without the need for external aids. It commonly uses a satellite onboard data processing unit and a filtering method to process the measurements of inter-satellite ranges. The onboard data processing unit is the main module of autonomous navigation systems. In this paper, the two main factors that affect the accuracy of autonomous orbit determination for a navigation constellation are discussed first, and then a distributed onboard algorithm for autonomous orbit determination of navigation satellites is proposed. This method is based on a long-term ephemeris prediction and is suitable for the satellite hardware capability. The main feature of this method is that both the distributed computing method and an onboard analytical state transition matrix are used to process inter-satellite range measurements. One of the main advantages of this approach is high-speed computing since the amount of calculations needed is significantly less than that of the centralised computing method and those distributed methods that need to use an onboard numerical integrator. Another advantage of this approach is that the use of the onboard analytical state transition matrix algorithm can save a great amount of resources for both ground-to-satellite data transmissions and data storage units in satellites’ hardware. This could result in substantial cost reduction for space missions. Finally, a simulation method used for testing the proposed algorithm is presented. Results of tests over a period of 90 days show that the user range error of autonomous orbit determination derived from the proposed method is less than three metres.

The latest attempts at improving small scale autonomously guided Uninhabited Aerial Vehicles (UAVs) have concentrated around the increase of range and speed. One of these ways is to incorporate dynamic slope soaring manoeuvres as part of the flight path. This is in contrast to most conventional path-planning algorithms where waypoint guidance is merged with terrain avoidance or contour following capability. Additionally, current trajectory optimization techniques are iterative and so have a considerable computational load. The proposed algorithm is based on Dubin's curves, and is therefore optimal by definition. Being non-iterative, it is comparatively a more efficient algorithm. Hence, a key advantage of the proposed technique is that the desired trajectory is generated quickly in real time with minimum computational load while satisfying the spatial constraints of dynamic slope soaring.

The accuracy and fault tolerance of filters are directly affected by the filter architecture and algorithm, thus influencing navigation performance. The chi square detection used in the conventional reset federated filter is not sensitive to soft faults, and it is easy to cause the health subsystem to be polluted through information sharing. It is a challenge to design an adaptive reset federated filter to improve the performance of the navigation system. Therefore, taking the Strapdown Inertial Navigation System/Global Positioning System/Celestial Navigation System/Synthetic Aperture Radar (SINS/GPS/CNS/SAR) integrated navigation system as an example, an adaptive federated filter architecture for vector-formed information sharing without a fault isolation module is designed in this paper. The proposed method uses the two-state chi square detection algorithm to calculate the parameters corresponding to each state, making the state with higher accuracy obtain a greater information distribution coefficient. In addition, according to the value of vector-formed information sharing, an adaptive coefficient of measurement noise is designed. This improves the adaptability of the navigation system to soft faults. Simulation results show that the accuracy of the proposed algorithm has the same performance compared with the conventional method under normal circumstances. When the sensor has a soft fault, the adaptive federated filter algorithm proposed in this paper can adaptively adjust the distribution coefficients, eliminate the influence of the fault information and improve the precision of the navigation system. The approach described in this paper can be used in multi-sensor integrated navigation. It will have better performance in engineering applications.

A ship's log is described which works on the principle of electromagnetic induction. The measuring head contains a coil with a vertical axis and is arranged so that voltages are picked up proportional to the two components of water flow past it. The electronic circuits are designed to give a true and stable zero by using a low-frequency squarewave energizing current. Laboratory tests show the output to be linearly related to water velocity. Because of the complicated flow patterns round a ship, the log must be calibrated in situ at sea. Calibration of the forward component meter follows the usual procedure and this meter is accurate to about ±0·1 knot or ± 1 per cent, whichever is greater. However, calibration of the athwartship component meter is difficult and time-consuming, and the sensitivity is dependent on forward speed. With care, it seems that an accuracy of ±0·2 knot or ± 10 per cent, whichever is greater, should be possible with this meter, but more experience of such calibrations is required. The paper is discussed on p. 319.

This paper describes the genesis, the principle of operation and characteristics of selected radio-navigation positioning systems, which in addition to terrestrial methods formed a system of navigational marking constituting the primary method for determining the location in the sea areas of Poland in the years 1948–2000, and sometimes even later. The major ones are: maritime circular radiobeacons (RC), Decca-Navigator System (DNS) and Differential GPS (DGPS), as well as solutions forgotten today: AD-2 and SYLEDIS. In this paper, due to its limited volume, the authors have omitted the description of the solutions used by the Polish Navy (RYM, BRAS, JEMIOŁUSZKA, TSIKADA) and the global or continental systems (TRANSIT, GPS, GLONASS, OMEGA, EGNOS, LORAN, CONSOL) - described widely in world literature.

This paper focuses on the performance analysis of ionosphere monitoring using the measurements from a BeiDou Continuously Operating Reference Stations (CORS) network. Combined pseudo-range and carrier phase observations are used to estimate total electron content (TEC) and the hardware delay deviation is also computed. Using the observations from five BeiDou CORS in China, the TEC monitoring results were obtained from each station and compared with GPS monitoring results and also those from the Global Ionosphere Maps (GIM) model. Numerical computation shows that the BeiDou system has the ability to precisely detect the TEC diurnal variation trend on each station. The Residual Mean Square (RMS) difference between the BeiDou and the GIM model at a higher latitude station is about four TEC Units (TECU), while the RMS difference between the GPS and the GIM is about three TECU; at a lower latitude station this difference increases to six TECU for BeiDou and four TECU for the Global Positioning System (GPS); at the lowest latitude station in this study, the differences for both systems are about six TECU.

This paper, and the following 5 papers, were first presented at a Symposium on ‘Advanced Moving-Map Displays’ held on the 3rd and 4th of August 1999 at the US Naval Research Laboratory Detachment at the NASA Stennis Space Centre, Mississippi and are reproduced in modified form with the kind permission of the NRL Commanding Officer, Captain Douglas H. Rau USN.

The role of human factors in map design is to serve as a mediator between the technology availed by electronic digital maps (particularly vector maps) on the one hand, and the many tasks performed by the user on the other. Simply put, no one map is best suited for all tasks. The appropriate mapping of map to task is, in turn, mediated by a series of information processing principles, articulated by the engineering psychologist. The field is on the threshold of being able to provide computational models, based on these principles, that will provide guidance to the map designer as to the circumstances that make one map format better than another for a particular application. This paper describes these principles as applied to two domains of vector map design: the domain of three-dimensional maps, and the domain of database overlay.

The concept of Relative Receiver Autonomous Integrity Monitoring (RRAIM) using time differential carrier phase measurements is investigated in this paper. The precision of carrier phase measurements allows for mitigation of integrity hazards by implementing RRAIM monitors with tight thresholds without significantly affecting continuity. In order to avoid the need for cycle ambiguity resolution, time differences in carrier phase measurements are used as the basis for detection. In this work, we examine RRAIM within the context of the GNSS Evolutionary Architecture Study (GEAS), which explores potential architectures for aircraft navigation utilizing the satellite signals available in the mid-term future with GPS III. The objectives of the GEAS are focused on system implementations providing worldwide coverage to satisfy LPV-200 operations, and potentially beyond. In this work, we study two different GEAS implementations of RRAIM. General formulas are derived for positioning, fault detection, and protection level generation to meet a given set of integrity and continuity requirements.

Geometric Dilution Of Precision (GDOP) is a factor that describes the effect of geometry on the relationship between measurement error and position determination error. It is used to provide an indication of the quality of the solution. Conventional closed-form GDOP calculation formula applied to all possible combinations of visible satellites is rather time consuming, especially as the number of satellites grows. Approximations, such as the maximum volume method, are faster but optimum selection is not guaranteed. In this paper, a more concise but efficient solution for the calculation of GDOP value in the case of four Global Positioning System (GPS) satellites is firstly reviewed and then extended to cover the other forms of dilution of precision (DOP) values, including vertical DOP (VDOP) and horizontal DOP (HDOP). Secondly, a review and extension of the conventional solution is performed in the case of three GPS satellites aided by an altimeter. Based on the ideas gained from these two approaches, a simpler closed-form DOP formula for three GPS satellites aided by an altimeter is derived. The advantage of the proposed formulation is that it is simpler and thus reduces the computational load in comparison to the conventional one.