This paper analyses flight trial results to study the overall performance and limitations of a GPS/Pseudolite/INS integration approach for aircraft precision approach and landing applications. For this purpose, the series of approaches were flown at Wedderburn Airfield, Australia. The analysed results show that pseudolite signals strengthen the ranging signal availability and the satellite geometry. Most of the geometry enhancement is found in the vertical position component, improving the accuracy of the aircraft's altitude. Furthermore, the results reveal that the inclusion of a pseudolite enhances both internal and external reliabilities. A dramatic improvement of the external reliability in the vertical component is observed.

This paper discusses human error from two perspectives: errors made by operators on the one hand and errors made by designers and manufacturers of technological aids on the other. The question of operators' reliance on technological aids is discussed, as well as the concept of “overreliance” in connection with technologically aided presentation of navigational information. The accident investigation report following the grounding of the M/V Royal Majesty in 1995 is taken as an example. In that and many reports, designers and technology were not investigated as carefully as the operators on site. In that report, total responsibility for the accident was attributed to the mariners, while unreliable, incorrectly designed or incorrectly mounted technological aids, as well as the constructors, manufacturers and technical expertise behind it, were not investigated. This biased praxis when investigating human error is questioned and another investigative approach is suggested, in which operators and technology are treated equally and where the people behind the technologies can also be scrutinised. Such an approach would have a great beneficial impact on safety at sea.

Integrated electronic marine systems are becoming part of the numerous screens which are to be found on ships' bridges and in wheelhouses of fishing vessels. This paper continues previous work which has focussed on perceived safety aspects of integrated electronic marine systems, in particular, a small study completed within the last two years which showed that some fishing skippers had negative perceptions of integrated electronic marine systems. This present study uses semi-structured interviews with skippers in the United Kingdom fishing fleet to show that integrated electronic marine systems can be perceived as increasing safety as well as being of good value in terms of need and cost. It is possible that such perceptions are dependent on experiencing the use of integrated electronic marine systems within off-shore trawling.

An optimal attitude estimator is presented for a human body-mounted inertial measurement unit employing orthogonal triads of gyroscopes, accelerometers and magnetometers. The estimator continuously fuses gyroscope and accelerometer measurements together in a manner that minimizes the mean square error in the estimate of the gravity vector, based on known spectral characteristics for the gyroscope noise and the linear acceleration of points on the human body. The gyroscope noise is modelled as a white noise process of power spectral density δn2/2 while the linear acceleration is modelled as the derivative of a band-limited white noise process of power spectral density δv2/2. The estimator is robust to centripetal acceleration and guaranteed to have zero mean error regardless of the motion of the sensor. The mean square angular error in attitude is shown to be independent of the module's angular velocity and equal to 21/2g−1/2δn3/2δv1/2.

There is currently considerable interest in the international regulations for preventing collisions at sea (the COLREGS). Suggestions for changes are made, but their validity is difficult to assess because there is little possibility of testing new proposals before they are introduced. There is, however, the possibility of considering the history of the COLREGS, and their effectiveness, as they have evolved over the years. In this paper, the author's aim is to look at the lessons that may be learned from one, particularly tragic, collision between the Princess Alice and the Bywell Castle in 1878. Opinions differ as to whether a study of history is likely to be a useful exercise.

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.

This paper is intended as an historical document describing the entry and success of the Decca Radar Company into the production of Doppler-based navigation units. It is based on an original personal paper written in about 1970 by Trevor Gray, then Head of Doppler Department, Decca Radar, updated and edited with additions by Walter Blanchard (past President of the RIN) assisted by Trevor Gray in May 2007. The paper first covers the basic theory and principles of Doppler radar systems, continues through the setting up of the Decca Doppler Department in the mid-1950s and the production of the first transistor-based Doppler system. Success led to the development of both civil and military Doppler systems culminating in the Decca Doppler 70 Series which was fitted to some 30 types of aircraft and helicopters, worldwide.

The Automatic Identification System (AIS) is an efficient tool to exchange positioning data among participating naval units and land control centres. It was developed primarily as an advanced tool for assistance to sailors during navigation and for the safety of the life at sea. Maritime security has become a major concern for all coastal nations, especially after September 11, 2001. The fundamental requirement is maritime domain awareness via identification, tracking and monitoring of vessels within their waters and this is exactly what an AIS could bring. This paper will be focused on how the AIS-derived information could be used for coastal security, maritime traffic management, vessel tracking and monitoring with the help of GIS technology. The AIS data used in this paper was collected by the Canadian national aerial surveillance program.

The integration of GPS and INS observations has been extensively investigated in recent years. Current systems are commonly based on the integration of INS data and the double differenced GPS measurements from two GPS receivers in which one is used as a reference receiver set up at a precisely surveyed control point and another is as the rover receiver whose position is to be determined. The requirement of a base receiver is to eliminate the significant GPS measurement errors related to GPS satellites, signal transmission and GPS receivers by double differencing measurements from the two receivers. With the advent of precise satellite orbit and clock products, the un-differenced GPS measurements from a single GPS receiver can be applied to output accurate position solutions at centimetre level using a positioning technology known as precise point positioning (PPP). This then opens an opportunity for the integration of un-differenced GPS measurements with INS for precise position and attitude determination. In this paper, a tightly coupled un-differenced GPS/INS system will be developed and described. The mathematical models for both INS and un-differenced GPS measurements will be introduced. The methods for mitigating GPS measurement errors will also be presented. A field test has been conducted and the results indicate that the integration of un-differenced GPS and INS observations can provide position and velocity solutions comparable with current double difference GPS/INS integration systems.

The Paris Memorandum of Understanding (Paris MoU) establishes each year in its annual report the traditional “Black-Grey-White” lists of flags. These tables are based on processed performances of flags over a 3-year period, showing the full spectrum between quality flags and flags with a poor performance. The performance of each flag is calculated by the Paris MoU on the basis of inspected and detained ships flying the considered flag, using binomial calculus. Furthermore, black listed flags are one of the criteria, among others, used by the Paris MoU for targeting vessels for their inspections. Using the same binomial calculation method as mentioned above but considering casualties instead of detentions and a multivariate approach instead of considering the flag only, it is possible to extend the Black-Grey-White lists of flags of the Paris MoU based on detentions, to Black-Grey-White lists of categories of vessels with regard to their observed casualties for a given period.

At the time when a correspondence group has been set up by the Sub-Committee on Flag State Implementation of IMO for defining “objectives, framework of mechanisms and methodology for a study on the combination of casualty and Port State Control related data”, this paper has the ambition to provide a valuable contribution to the group in discussions on the case for the necessity of combining casualty data and PSC related data with a view to complement current processing of flag State performance and the targeting criteria for ships inspections.

The introduction of AIS in 2002 and the drive to introduce electronic navigation aids to merchant ships had the principal stated objective of improving safety by enhancing situational awareness. This paper reviews the various types of electronic equipment fitted to vessels during the past five years in order to assist the watch-keeper, comments on the reduction in core watch-keeping skills and argues for a back-to-basics approach for watch-keepers. A version of this paper was first presented at the RIN conference NAV 07 in October 2007.

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.

With conventional snapshot RAIM algorithms, it is difficult to detect small errors and simultaneous multiple faults. Assuming that we know the system dynamics, filtering algorithms, such as the Kalman filter, can provide better integrity-monitoring performance than the snapshot algorithms because the filter reduces the noise level of measurements. However, because the Kalman filter presumes that measurement noise and disturbance follow the Gaussian distribution, its performance might degrade if the assumption is wrong. To address this problem, we propose a fault detection and exclusion algorithm using Gaussian sum filters. Because GNSS measurement noise does not follow the Gaussian distribution perfectly, the Gaussian sum filter can estimate the posterior distribution more accurately; therefore it has better integrity-monitoring performance. This paper describes the detailed algorithms and shows simulation results to evaluate the integrity-monitoring performance of the algorithms. The proposed algorithms detect about 30% smaller faults and generate 35% lower protection levels than the conventional methods. The results show that the proposed algorithms can provide better accuracy and availability performance.

This paper presents a new method of vessel heave compensation based on a new breed of commercially available low cost GPS receivers that can measure and record the carrier phase observable. The technique is based on the extraction of a highly accurate velocity estimate from standalone receivers using time differenced carrier phase observable. Two trials have been undertaken, one using a Spirent GPS signal simulator and another conducted at sea. The simulator trial thoroughly tested the use of commercially available low cost receivers for this method of velocity estimation through their comparison with higher grade receivers and quantified the errors under varying dynamics. The sea trial tested the heave algorithm against other heave sensors and an accurate reference provided by an Applanix POSRS and showed it to be capable of producing a heave output to rival inertial based heave sensors using commercially available low cost GPS receivers.

The concept of ship's domain plays an important role in navigating a ship. It is a criterion of safety in the process of making decisions by the navigator – in analyzing and assessing a navigational situation and in performing the right manoeuvre. This concept is particularly useful in restricted areas, including narrow fairways, which results from the fact that in such waters a manoeuvring area is restricted so that the criterion of the closest point of approach (CPA) cannot be used. This author has analyzed definitions of ship's domain and methods of its determination found in the literature on the subject. Then a method of navigational safety assessment using the fuzzy domain concept is proposed in reference to a ship in a restricted area. The concept and method of determination have been, respectively, defined and described. The method is based on relevant navigators' knowledge. The methods and tools for knowledge acquisition and representation make use of artificial intelligence. Ships and navigational areas of various size have been considered.

After Selective Availability (SA) was turned off, the rate of change with time of the DGPS common errors (atmospheric delay, satellite orbit and clock error) became quite slow. This inevitably leads to a requirement to modify various configurations of DGPS correction message broadcasting, and reference station (RS) managers need to examine the characteristics of GPS measurement errors with SA-off. GPS error sources are temporally and spatially decorrelated, so the DGPS user position accuracy is varied by the baud-rate of the RS, the distance between the user and the station, and the noise statistics of the receiver. We identify the minimum and maximum size of correction data, interval time, the coverage range and the baud-rate that are required to maintain the existing DGPS service. Moreover, the compatibility and accuracy can be assessed to meet the users' requirements without measurements being needed. The results in this paper are used in the study and testing for the redesign of United States Coast Guard (USCG) RS. We hope that our study will be a great help in determining the flexible factors of both the RS and the user.

The fundamental approaches for preventing collisions at sea are based on interpreting and understanding the Collision Regulations correctly. Although the Regulations are the technical standards of collision avoidance conduct at sea, they are also the code for dividing liability1. When one tries to apportion the collision liability between two parties, the first question faced is whether the Rules apply and if so, when do they apply? In order to answer this question, this paper has reviewed most of the English, American and Canadian cases in the past hundred plus years, which are related to this topic and outlined briefly four special circumstances where collision avoidance rules do not apply, even if there is a risk of collision.

Severe space weather conditions affect the performance of numerous modern technical systems, causing problems not only for national and global economies, but for everyday life as well. Satellite navigation systems are particularly vulnerable, despite the fact that systematic monitoring of space weather in general is still performed on a global scale. Space weather effect correction models applied within the standard satellite positioning service are not capable of tackling the effects of severe space weather conditions and local ionospheric characteristics. Severe space weather effects on the GPS ionospheric delay are intensely studied in order to provide advanced models of the space weather effects on GPS positioning performance.

Here one study of severe space weather conditions and its consequences on the GPS ionospheric delay in Croatia is presented. The study takes advantage of the availability of the space weather indices and the GPS pseudorange measurements (taken at the reference site at Osijek, Croatia) related to a major severe space weather event lasting from early October 2003 to late November 2003. This paper presents the reconstruction of the severe space weather conditions and the development of ionospheric disturbances. Based on these reconstructions, the dynamics of the GPS ionospheric delay has been derived. The comparison of actual (measured) and modelled (according to standard GPS model) GPS ionospheric delay has been performed, with the aims of identifying actual behaviour of GPS ionospheric delay and examining the ability of standard (Klobuchar) GPS model to describe the GPS ionospheric delay in severe space weather conditions. Two interesting experimental models derived from the data analysis are presented, addressing the direct relations between the GPS ionospheric delay and the parameters of space weather activity (sunspot number and solar flux), as observed at the reference station Osijek, Croatia.

The paper concludes with the plans for further research activities related to the regional GPS ionospheric delay model development for south-eastern Europe.

The Kalman filter (KF) is a form of optimal estimator characterized by recursive evaluation, which has been widely applied to the navigation sensor fusion. Utilizing the KF requires that all the plant dynamics and noise processes are completely known, and the noise process is zero mean white noise. If the theoretical behaviour of the filter and its actual behaviour do not agree, divergence problems tend to occur. The adaptive algorithm has been one of the approaches to prevent divergence problems in the Kalman filter when precise knowledge on the system models is not available. Two popular types of adaptive Kalman filter are the innovation-based adaptive estimation (IAE) approach and the adaptive fading Kalman filter (AFKF) approach. In this paper, an approach involving the concept of the two methods is presented. The proposed method is a synergy of the IAE and AFKF approaches. The ratio of the actual innovation covariance based on the sampled sequence to the theoretical innovation covariance will be employed for dynamically tuning two filter parameters – fading factors and measurement noise scaling factors. The method has the merits of good computational efficiency and numerical stability. The matrices in the KF loop are able to remain positive definitive. Navigation sensor fusion using the proposed scheme will be demonstrated. Performance of the proposed scheme on the loosely coupled GPS/INS navigation applications will be discussed.

In this paper the author introduces a new method of collision avoidance for multi-target encounters. The method combines the qualities of a sequence of necessary manoeuvres with some optimisation elements and supports any given ship domain. First the problem of determining the optimal course alteration manoeuvre for given ship domain model and multi-target encounter situation is solved. The solution consists of analytical formulas and numerical algorithms combined to achieve low computational complexity. Then this solution is further used to construct a method of planning ship trajectories, which are safe, economic and intuitive for navigators. Example scenarios and the resulting trajectories are also provided. All of the algorithms, formulas and their derivations in the text are presented explicitly, so that they could be directly applied in any collision avoidance system.