In a recent paper the author reported a distribution theory which rationalizes some fairly well established phenomena in navigational errors. Adequacy of the implied model and other existing models was investigated in the light of empirical evidence. A summary of the findings has been available in a previous issue of this Journal.

This paper provides further insights into several theoretical models, establishes formal procedures for the estimation of parameters crucial to the evaluation and design of navigational systems and investigates the potentials of a broader system of distribution models. In addition, some simplified results aiming at practical use for navigators and air traffic control authorities are provided. A real-world application of the suggested methods and theoretical results is also demonstrated.

Two Receiver Autonomous Integrity Monitoring (RAIM) architectures, Advanced RAIM (A-RAIM) and Relative RAIM (R-RAIM), are compared with two different RAIM algorithms, the Classic method and the Multiple Hypothesis Solution Separation (MHSS) method. The difference between A-RAIM and R-RAIM is in the positioning methods that produce different error models and projection matrices for integrity monitoring. The difference between RAIM algorithms lies in the methods of risk distribution. The influences of different positioning methods on integrity results are analysed in this paper via a generalized RAIM framework. Simulation results for the LPV-200 service with worldwide coverage show that the R-RAIM position domain method has the best results, while the differences between these methods decrease with application of the optimization method.

This paper describes a Multi-Criteria-Analysis (MCA)-based Decision Support System (DSS) developed for the management of incidents in maritime traffic. The developed DSS helps to organise a large quantity of information related to emergency management, spatial data and “live” data (radar data, weather forecasting data), to make it available to decision makers in a comprehensible and user-friendly way. Special care has been taken to model human Decision-Making (DM) processes during incident situations. Since the DM process is always multi-criterial, a Multi-Criteria Decision-Making (MCDM) method called Preference Ranking Organisation Method for Enrichment Evaluations (PROMETHEE) is used. However, a simplified variation of PROMETHEE II has been utilised to make results more understandable to non-expert users. The aim of this research is to incorporate effective DSS in human DM processes, thus reducing the possibility of making poor decisions. The concept of Web MCA-based DSS is presented as a case study: Web DSS developed for the east coast of the Adriatic Sea.

Knowledge of forces and yaw moments which exist between a pair of vessels moving parallel to each other is crucial to the design of their automatic motion control system. Studies involving measurements of forces and moments occurring between a pair of ships were undertaken. The research was carried out on the basis of two real floating training ship models made at 1:24 scale in real conditions on the Silm Lake in Ilawa Kamionka. As a result, suction forces and yaw moments occurring between the pair of vessels calculated according to semi-empirical formula were verified. It was found that the process of overtaking and parallel motion (which is a quasi-stationary motion) could not be modelled in the same way. Nevertheless, the results confirmed the presence of forces and moments with values similar to those in the catch-up and parallel motion phases during the ships’ overtaking manoeuvre. Thanks to this confirmation, it was possible to use the results of the analytical calculation for the catch-up phase during design of the ships' parallel motion automatic control system.

Recent developments in GPS positioning show that a user with a standalone GPS receiver can obtain positioning accuracy comparable to that of carrier-phase-based differential positioning. Such technique is commonly known as Precise Point Positioning (PPP). A significant challenge of PPP, however, is that about 30 minutes or more is required to achieve centimetre to decimetre-level accuracy. This relatively long convergence time is a result of the un-modelled GPS residual errors. A major residual error component, which affects the convergence of PPP solution, is higher-order Ionospheric Delay (IONO). In this paper, we rigorously model the second-order IONO, which represents the bulk of higher-order IONO, for PPP applications. Firstly, raw GPS measurements from a global cluster of International GNSS Service (IGS) stations are corrected for the effect of second-order IONO. The corrected data sets are then used as input to the Bernese GPS software to estimate the precise orbit, satellite clock corrections, and Global Ionospheric Maps (GIMs). It is shown that the effect of second-order IONO on GPS satellite orbit ranges from 1·5 to 24·7 mm in radial, 2·7 to 18·6 mm in along-track, and 3·2 to 15·9 mm in cross-track directions, respectively. GPS satellite clock corrections, on the other hand, showed a difference of up to 0·067 ns. GIMs showed a difference up to 4·28 Total Electron Content Units (TECU) in the absolute sense and an improvement of about 11% in the Root Mean Square (RMS). The estimated precise orbit clock corrections have been used in all of our PPP trials. NRCan's GPSPace software was modified to accept the second-order ionospheric corrections. To examine the effect of the second-order IONO on the PPP solution, new data sets from several IGS stations were processed using the modified GPSPace software. It is shown that accounting for the second-order IONO improved the PPP solution convergence time by about 15% and improved the accuracy estimation by 3 mm.

This paper investigates an RTK-GPS correction generation technique suitable for low-rate (<600 bps) data-link. We combined correction filtering algorithm with an efficient transmission technique which is based upon correction scheduling. The correction scheduling technique can reduce the required amount of correction data as well as the latency effect on RTK-GPS positioning accuracy. We processed real time GPS data to evaluate the performance of the RTK-GPS correction generator for low-rate data-link. The experimental results demonstrate that the proposed techniques can lower the required bandwidth of data-link up to 500 bps, maintaining the high accuracy of RTK-GPS.

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

Wavelets and wavelet transforms can be used for vector-map data compression. The choice of wavelet, the level of decomposition, the method of thresholding, the height of the threshold, relative CPU times and file sizes, and reconstructed map appearance were investigated using the Wavelet Toolbox of MATLAB. Quantitative error measures were obtained. For two test vector-map data sets consisting of longitude and latitude points, compressions of 35 to 50 percent (1·5[ratio ]1 to 2[ratio ]1) were obtained with root-mean-square errors less than 0·003 to 0·01° longitude/latitude for wavelet packet decompositions using selected wavelets.

To meet the requirements of different applications, the International Global Navigation Satellite System (GNSS) Service (IGS) has provided Global Positioning System (GPS) satellite ephemerides and clock products with different accuracy levels (final, rapid and ultra-rapid products). Comparison of Precise Point Positioning/Inertial Navigation System/Ultra Wideband (PPP/INS/UWB) tightly coupled positioning with different precise satellite ephemeris and clock products is made and corresponding data analysis is provided. Final, rapid and ultra-rapid products are applied in a PPP/INS/UWB integrated system. The field trajectories, position and velocity errors of the integrated system with different products are compared. The results indicate that PPP/INS/UWB tightly coupled positioning with final and rapid products achieves an accurate performance. Compared with the position resolution using final products, the position accuracy with the ultra-rapid products (observed half) is slightly reduced and the position accuracy with the ultra-rapid products (predicted half) has a 0·1–0·2 m reduction. The influence of precise satellite ephemeris and clock products is very minor for non-real-time positioning, relative to the accuracy of PPP/INS/UWB tightly coupled positioning.

Any device having a property which varies as a result of its being rotated in space can, in principle, be used as the primary sensor of an inertial navigation system. A wide range of devices and properties has received attention with this aim in view. The spinning-wheel gyroscope has, to date, proved the most fruitful but a number of ‘exotic’ types of gyro show promise. The discovery that the atomic nucleus can, under certain conditions, behave like a spinning mass gave birth to ideas of a nuclear gyro of some sort. The further discovery that some nuclei possess magnetic properties opened the way to nuclear magnetic resonance and offered a method of communicating with the minute spinning masses.

The present-day emphasis on the need to analyse and identify risk situations in ports is hardly a new phenomenon. In fact, port managements have, as a matter of course, been very conscious of this need but over the years, with the ever-increasing transport by sea of hazardous hydrocarbon, chemical as well as nuclear-related products, this need has simply become much more pronounced. Moreover, present-day public awareness and concern about the possible incident impact on the environment in the form of pollution or personal injury has even further increased the awareness of the corporate responsibility and the need to assess the operational risk levels of ports. Of equal importance, of course, is the need and the capability to predict operational risk levels for new port developments or modification projects or of the possible risks associated with the introduction of hazardous cargo-handling facilities at existing or new port terminals.

After Global Navigation Satellite Systems (GNSS) were first used in the field of hydrography in 1980, developments in hydrographic surveying accelerated. Survey precision in hydrography has been improved for both horizontal and vertical positioning and seafloor acoustic measurement by means of these new developments. Differential Global Positioning System (DGPS), Real Time Kinematic (RTK) and Network RTK (NRTK) techniques are the satellite-based positioning techniques that are commonly used in shallow water surveys and shoreline measurements. In line with these developments, the newer Precise Point Positioning (PPP) has been introduced. Combining precise satellite positions and clocks with dual-frequency GNSS data, PPP can provide position solutions from the centimetre to decimetre level. In this study, the coordinates of control points were determined by using the Post-Process PPP (PP-PPP) technique. Seven test points, which are the points of the Continuously Operating Reference Station - Turkey (CORS-TR) network, are selected near the shorelines within Turkey. The 24-hour data was split from one to six hours by one hour periods. Automatic Point Positioning Service (APPS) was selected to process the data. The poisoning error of the test points were given and compared with International Hydrographic Organization (IHO) S44 hydrographic survey standards.

Vehicle state estimation and path prediction, which usually involve Kalman filter and motion model, are critical tasks for intelligent driving. In vehicle state estimation, the comparative performance assessment, regarding accuracy and efficiency, of the unscented Kalman filter (UKF) and the extended Kalman filter (EKF) is rarely discussed. This paper is devoted to empirically evaluating the performance of UKF and EKF incorporating different motion models and investigating the models’ properties and the affecting factors in path prediction. Extensive real world experiments have been carried out and the results show that EKF and UKF have roughly identical accuracy in state estimation; however, EKF is faster than UKF generally; the fastest filter is about 2⋅6 times faster than the slowest. The path prediction experiments reveal that the velocity estimate and the used motion model affect path prediction; the more realistically the model reflects the vehicle's driving status, the more reliable its predictions.

Since January 1962, waves have been recorded by a shipborne wave recorder (Tucker, 1956) on the Sevenstones light-vessel which is stationed about 20 miles south-west of Land's End in about 200 ft. of water. Records were taken at three-hourly intervals and were mostly of 12 minutes’ duration. The analysis presented here is based on 2920 records taken in the first year of operation; the method of analysis which has been used is that described by Tucker (1961). This gives for each record:

(a) H1 = The sum of the distances of the highest crest and the lowest trough from the mean water level.

(b) Tz = The mean zero-crossing period.

(c) Tc = The mean crest period.

It has been recognized for some time that calculations of potential encounter rates based on the speed and lateral distributions of ships using sea routes provide only a partial estimation of the actual collision risk, as all encounters are usually given equal rating, and no attempt is made to include factors such as the degree of domain penetration or the relative speed of the ships. One possible solution to the problem consists in attempting to weight the calculated potential encounter rates according to the most relevant factors, and thus replace the calculated rates by weighted values to provide a relative estimate of collision risk. Goodwin, Lamb and Kemp reported a first attempt at such a procedure in their calculation of weighted encounter rates based on the observed traffic distributions and flow rates in the Sunk Lightship area in the neighbourhood of Harwich. A two-part index was used in the work; the first part employed a weighting factor based on the ratio of the time required for the completion of a manoeuvre involving a specified angle of course change, to the time available as measured from the ‘decision-distance’ at which the manoeuvre was deemed to commence. The second part used a factor based on the time required to pass and draw clear after completion of the manoeuvre.

This paper is based on a presentation made at the IAIN International Navigation Congress held in Sydney, Australia, in February 1988.

The global positioning system (GPS) offers a new opportunity for the automation of aircraft landing systems. The position and velocity measurements provided by a state-of-the-art GPS receiver using the C/A code and working in a normal or differential mode (D-GPS) and aided by one or two ground-based PseudoLites (PLS), may be able to satisfy the landing accuracy requirements of the FA A.

This paper describes the design and simulation of an aircraft automatic landing system. Aircraft position and velocity are assumed to be measured using a (carrier-tracking) GPS receiver. The hypothesized capability is based on measurements taken at Stanford and elsewhere, using the Trimble 4000SX, five-channel receiver in an integrated-doppler-aiding mode. For some of the autopilot designs, either ground-based GPS transmitters (pseudolites) or a radar altimeter have also been incorporated.

Included in the landing simulations are wind shears and a gust model, creating realistic landing situations. The performances of the lateral and vertical displacements are presented with their 1σ r.m.s. estimation errors during the glide-slope and flare phases. Included are different wind conditions, GPS configurations and controllers. The results are compared with the FAA requirements for various categories of automatic landing systems.

Primarily in response to airline pressures for fuel economies, ICAO, the International Civil Aviation Organization, established a study programme early in the 1980s to determine the feasibility of halving the vertical separation minimum (VSM) used above FL 290 to 1000 ft. This paper is the first of a 3-part article describing a European contribution to this programme. After outlining the aims and organization of the experimental work, it describes the choice of methodology available to measure height-keeping errors and gives an indication of the measurement accuracy achieved. Details of the data collections, the risk calculations performed and the factors found to affect height-keeping accuracy are given in Parts II and III. Overall, the work has shown that whereas it would be technically feasible to introduce a 1000-ft VSM in the North Atlantic region, other measures would be necessary before it could be used in continental airspace. Today, in certain areas, the need for a reduced VSM has become even more pressing in order to achieve the gains in airspace capacity necessary to handle rapidly growing volumes of air traffic.

Nautical services should be allocated efficiently as they have great resource costs. In this paper, the Marine Pilotage Service in the Istanbul Strait has been analysed by using Rockwell Arena Simulation Software. The purpose of the study is to find the required number of marine pilots for vessel traffic flow in the Istanbul Strait. It is evaluated thoroughly by a stochastic, dynamic, discrete simulation for safe service standards in pilotage. The result of the paper shows that discrete simulation technique is an efficient and reliable way of solving complex techno-nautical service allocation problems as proven by experts. As the discrete simulation result data shows, most other techno-nautical services can also be modelled and optimised by using similar techniques. Areas like optimisation of the number of pilots, tugs, resource allocation problems, berthing area selections and many more complex and inherently stochastic problems can be reliably solved by simulation experiments.

The acquisition of signals is a precondition for tracking and solution calculation in software-based Global Navigation Satellite System (GNSS) receivers. The Parallel Code phase Acquisition (PCA) algorithm can simultaneously obtain the correlation results at every sampling point. However, if the number of sampling points that needs processing is large, this method will lead to a heavy computational load. Thus, we improve the process of the PCA algorithm and propose a novel algorithm that divides the signals into K (K is a constant) parts to achieve correlation and obtains the correlation results with a fusion algorithm. This algorithm can simultaneously obtain the correlation results for sampling points at an interval of K points. If the K value is selected appropriately, the computational load can be decreased by about 50%. Also, the Receiver Operating Characteristic (ROC) curves show that under a certain probability of false alarm, the detection probability of the proposed algorithms is 5% lower than that of the PCA algorithm. Therefore, the proposed algorithm can speed up the acquisition process with a slight decrease in detection probability.

This paper considers the effect of receiving a secondary source of information upon ability to acquire and use spatial knowledge (i.e. the formation of a cognitive map). Participants watch videos of three journeys through an unfamiliar area. They then perform tasks measuring ability to integrate the routes into a cognitive map of the area. Subjects viewing the routes whilst hearing route guidance information performed consistently worse than those receiving no guidance. The presence of non-salient information, however, did not impair performance.

Existing studies highlighting differences between gender and age groups regarding spatial ability receive only partial support: the results suggest that ability to drive negates these effects. Female drivers perform as well as, if not better than, their male counterparts, and outperform male non-drivers. This same ‘driving’ effect was also evident in the over-55s group, with both male and female drivers performing significantly better than non-drivers in this age group. The results also show that driving ability enhances ability to cope with and use guidance information, suggesting that systems’ designers should make varying levels of spatial information available for less experienced drivers.

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.