The GNSS-R technique brings out the need for signal receiver systems to process both direct and reflected GNSS signals. This paper describes the architecture of a new GNSS-R receiver system (GRrSv.2) that features enhanced capabilities for remote sensing based on reflected Global Positioning System (GPS) signals. Signal processing issues including DDM calculation, Carrier and Code Generation and DDM Synchronization are presented. Aircraft- and land-based verification experiments for ocean winds, ocean Significant Wave Heights (SWH) and soil moisture have been performed and some primary results are presented in this paper.

The frequency division multiple access (FDMA) strategy used in GLONASS causes inter-frequency phase bias (IFPB) and inter-frequency code bias (IFCB) between receivers from different manufacturers. The existence of IFPB and IFCB significantly increases the difficulties of fixing GLONASS ambiguity and limits the accuracy and reliability of GLONASS positioning. Moreover, the initial value of IFPB and IFCB may be unavailable or unreliable with the increasing number of receivers from different manufacturers in recent years. In this study, a real-time and reliable calibration algorithm of IFPB and IFCB based on multi-GNSS assistance is proposed by providing a fixed solution. Real-time IFPB rate and IFCB can be obtained using this algorithm without the initial IFPB and IFCB. The IFPB rate for all GLONASS satellites and IFCB for each GLONASS satellite are estimated due to different characteristics of IFPB and IFCB. IFPB calibration can be divided into constant and real-time IFPB calibrations to meet the different positioning requirements. Results show that constant IFPB rate has only 2 mm difference from the mean value of real-time IFPB rate. The IFPB rate and IFCB estimated by this algorithm have excellent stability, and the change in reference satellite cannot affect the results of IFPB rate and the stability of IFCB. The centimetre-level positioning results can be obtained using two calibration methods, and the positioning results with real-time calibration method are 10%–20% better than those with the constant calibration method. Under satellite-deprived environments, the improvements of multi-GNSS positioning accuracy with constant inter-frequency bias calibration gradually increase as the satellite cut-off elevation angle increases compared with GPS/BDS, which can reach up to 0·9 cm in the vertical direction.

Vector map databases offer the potential for customised cockpit moving-map displays, in which user-specified cartographic features can be layered to meet mission requirements. The disadvantage of vector moving-maps is the potential for increased user workload. In 1995, the Naval Research Laboratory and the Naval Air Weapons Center jointly performed a preference study, during which aircrew viewed demonstrations of prototype moving-map displays and responded to a detailed questionnaire concerning the usefulness of each display. This paper summarises aircrew interviews from that study pertaining to both vector moving-map displays and vector feature overlays, including Height-Above-Threshold (HAT), threat rings, and Clear Line-of-Sight (CLOS).

In the sixteen years since the last paper on this subject was published in the Journal (1951, 4, 288), some notable changes have taken place in the design and capabilities of submarines. Nautilus, the world's first nuclear submarine, was laid down in 1952 and completed in 1955. Since then a further 120 nuclear submarines have been commissioned. Now, a large proportion of the world's submarines are ‘true’ submersibles, self-sustaining over periods of months in everything except food; capable of proceeding submerged faster than the average surface ship; and rarely requiring to surface or even to come to periscope depth.

For the integration of different navigational aids of an aircraft by a general purpose computer the following way is proposed: The basic navigational system is a doppler or inertial dead reckoning system (D.R.S.). The other navigational aids serve for control measurements, with the help of which the error of the D.R.-position and the most important systematic error sources of the D.R.S. are determined by least square adjustment during flight. These error quantities are then used for a corresponding correction of the D.R.S. The supplementary navigational aids are consequently used both for the correction of the D.R. position and for the calibration of the D.R.S. The method is described for the example of the integration of a doppler D.R.S. with Tacan.

From the great number of different navigational aids, which are today available or in development, we can draw the conclusion that none of these navigational systems can satisfy all requirements. Therefore, for many years it has been the custom to combine several navigational aids, and thus the human navigator has the task of evaluating the different navigational information. This evaluation is, however, often disturbed by unfavourable conditions. In a high-speed aircraft for example the navigator is overburdened by a lack of time and space, errors in the navigational sensors, &c. This necessarily means that the evaluation of the data is reduced to a minimum, and that a great deal of the available information is lost.

The problem of avoiding collisions at sea, particularly in restricted visibility, is not likely to have one simple solution. Indeed there are three main areas which need separate consideration because of their different requirements. First, in rivers and estuaries, port approaches and narrow passages traffic is rigidly confined. Second, in waters adjacent to coastlines and in some other areas dense traffic has limited space in which to manœuvre. Third, in the open sea there are fewer encounters and unlimited manœuvring space. It seems probable that the best solution to the first of these problems will be found in shore surveillance of the traffic and regulation of the traffic flow by a licensed authority. Prescribed routes with perhaps speed limits and policing may solve the second, but only ratification of an internationally accepted rule of behaviour will satisfy the third requirement. This paper proposes to develop a set of manœuvres which may be applied as a rule which will be accepted as a possible solution to the third requirement.

E-navigation provides the opportunity to apply modern digital and other electronic enhancements to improve the safety and efficiency of maritime navigation. Under the broad banner of e-navigation, the International Hydrographic Organization's S-100 product specification framework is facilitating the establishment of a standard maritime data structure to enable a free-flowing exchange of navigation information between ships, ship-to-shore and shore-to-ship. There are currently over 30 S-100 based product specifications at various stages of development. For the data standard to be properly used, navigation software products must be capable of reading as well as comprehending the data format and content. To develop robust and stable software, the S-100 data models and product specifications must be consistent, accurate and interoperable in conveying various types of information. This paper describes the results of research on S-100 based product specifications from the viewpoint of developing maritime navigation software. In particular, issues related to software development for Electronic Chart Display Information System (ECDIS) and Vessel Traffic Service (VTS) are discussed, including appropriate data model analysis, processing of features, and symbols overlapping with other product specifications. Proposed solutions for some identified issues are presented.

Vessels are found frequently operating under the Automatic Identification System (AIS) ‘Not Under Command’ (NUC) option near ports and close to shores in order to report their manoeuvre status to nearby traffic. When asked if they are under any kind of restriction regarding their engines or steering, they often answer that they are just drifting or waiting for the pilot or shipowner's orders. The question that arises is this: “Are these vessels really under an NUC situation or can the AIS Navigational Status menu adapt to the different circumstances of navigation?”.

Concentrating on a surface vessel with input saturation, model uncertainties and unknown disturbances, a path following the adaptive backstepping control method based on prescribed performance line-of-sight (PPLOS) guidance is proposed. First, a prescribed performance asymmetric modified barrier Lyapunov function (PPAMBLF) is used to design the PPLOS and the heading controller, which make the path following position and heading errors meet the prescribed performance requirements. Furthermore, the backstepping and dynamic surface technique (DSC) are used to design the path following controller and the adaptive assistant systems are constructed to compensate the influence of input saturation. In addition, neural networks are introduced to approximate model uncertainties, and the adaptive laws are designed to estimate the bounds of the neural network approximation errors and unknown disturbances. According to the Lyapunov stability theory, all signals are semi-globally uniformly ultimately bounded. Finally, a 76$\,{\cdot }\,$2 m supply surface vessel is used for simulation experiments. The experimental results show that although the control inputs are limited, the control system can still converge quickly, and both position and heading errors can be limited to the prescribed performance requirements.

A probabilistic methodology for separation loss probability assessments is proposed in this paper. The key focus is on the effect of uncertainties from multiple Automatic Dependent Surveillance-Broadcast (ADS-B) systems on the separation loss probability assessment. First, a brief review of the ADS-B system and its associated uncertainty quantification metrics is discussed. It is found that most existing studies focus on the individual ADS-B uncertainty quantification for a single aircraft, which is not sufficient for separation loss probability assessment when two or more aircraft are involved. Next, a probabilistic positioning model with multiple aircraft is proposed and various types of uncertainties are included in the proposed model. Numerical simulations show that a navigation satellite fault can significantly affect separation error when individual aircraft see different satellite sets. Following this, several demonstration examples are illustrated to show the bounds for separation loss probability estimation. Finally, several conclusions and suggestions are discussed based on this study. One major finding is that the separation risk significantly increases when two nearby aircraft use different satellite sets to navigate. Real-time assessment of this risk should be performed.

This note provides some qualitative impressions of the need for precise navigation in the S.S.T. operation having due regard to performance and noise. It highlights the increased signific ance of the vertical plane, but quantitative conclusions as to horizontal ability cannot be made in the absence of knowledge of traffic amounts. It suggests that any tactical ‘chasing’ of noise reduction through performance variations not planned before flight is impracticable.

In common with other aircraft types, the S.S.T. has three distinct phases of flight apart from take-off and landing: climb to cruise altitude, cruise and descent. The S.S.T. climb is characterized by an acceleration phase dividing the subsonic portion of flight from the supersonic. Similarly, the descent profile includes a deceleration phase which restores flight to the subsonic region. Contained in these three phases of flight unique to the S.S.T.—acceleration, supersonic flight and deceleration—are some of the special factors affecting aircraft navigation.

This paper commences by outlining the developments expected in en-route navigation capabilities in Western Europe and describes the current provision of surveillance employing monopulse SSRS. Following a brief review of GPS characteristics, it then considers the use of ADS, in conjunction with GPS, as an alternative and/or supplement to these ground-based systems. In the light of a simple cost comparison, it suggests that the space-based system could be very advantageous, particularly where new routes are to be established in areas with little or no ATS infrastructure. A final section discusses the possibility of using GPS for height-monitoring purposes as will be necessary when a reduced vertical separation minimum of iooo ft, is employed above FL290 in Europe, and elsewhere.

Traffic separation schemes have been established all over the world with the aim of reducing the danger of collision. Field observations have shown that despite the adoption by IMO and the laying down of the schemes on nautical charts a good many vessels do not comply with the steering and sailing rules applicable at traffic separation schemes. This paper attempts to review the apparent difficulties met. Some suggestions for improving of the situation are made.

The separation of traffic into two streams moving in opposite directions has been introduced with the aim of reducing the incidence of collisions. Such a measure results in a decrease of the rate of encounters and an almost total elimination of head-on or fine crossing meetings which are considered dangerous especially in restricted visibility. Investigations have confirmed the effectiveness of the measure in achieving the purpose provided that the steps taken are reasonable from a practical point of view.

This paper formed the 1992 Anderson Memorial Lecture. It was presented by Air Commodore Grocott at a meeting of the Solent Branch at the Warsash Campus of Southampton Institute of Higher Education on 12 March.

Following the publication of the Government's White Paper on Integrated Transport in July 1998, and a shift in emphasis by Local Authorities away from road building to demand management techniques, the current trend is to a more balanced approach, whereby the use of road-space may be charged to vehicle drivers, i.e. road users pay to use (at least some) roads, just as public transport passengers pay each time they travel. Key to this is the introduction of some form of road user charging or vehicle access control. In urban areas, this may be achieved using paper licences (as in Singapore, 1975–1998), electronic (microwave) tags and transponders (as in Trondheim and Oslo, Norway and in Singapore since 1998) or by the use of automatic video-based licence-plate recognition (ALPR). The use of video-based registration to check whether a vehicle has purchased (or been granted) some form of licence rights to use a particular road or cordoned area on a particular day seems both logical and attractive. However, this form of urban road use pricing has not been operated in anything other than small-scale pilot schemes, and there are a significant number of technical, organisational and operational issues that need to be researched before such a system could safely be implemented for everyday use. This paper is specifically aimed at addressing such key issues, to determine whether in the short term (next 5 years) ALPR could deliver a practical tool for use by local authorities, whether in isolation or as part of a package of applications, to reduce traffic congestion within urban areas.

Container shipping is one of the most important transport modes in international trade. For a large-scale container shipping network, an optimisation model is proposed to minimise the total shipping cost of container flow. Considering the directional property of the container shipping process, a steering vector search pattern is incorporated in a Max-Min Ant System (MMAS) solving algorithm, and an orthogonal array method is adopted in parameter settings. In numerical experiments, a traditional ant colony algorithm and an MMAS algorithm based on a steering vector search pattern are used respectively to optimise the network of five node scales. The results show that a steering vector search pattern can speed up the computation process and improve the optimisation effect.

Radiolocation systems for aviation based on Multi-Lateration (MLAT) typically use a set of synchronised ground sensors to receive radio signals broadcast by onboard transmitters. In most cases, the sensor synchronisation in Wide Area Multi-Lateration Systems (WAM) is provided by Global Navigation Satellite System (GNSS) receivers. However, in the case of synchronisation failure, there is still a possibility to estimate the coordinates of the tracked aircraft by using the measurements of the time of arrival taken by non-synchronised sensors. The article presents the principle of operation and equations for calculating the coordinates of an aircraft in an asynchronous multi-lateration system, together with the results of a computer simulation allowing comparison of the accuracy of position estimation between the asynchronous and the typical, synchronous MLAT. This paper contains also some comments on the required stability of the clock source for the sensors working in an asynchronous MLAT system.

One of the limitations of Differential Global Positioning Systems (DGPS) is that accuracy decreases as the distance between the user and a base station increases. We have developed a new DGPS positioning strategy that is less affected by baseline length and enables better accuracy. We found correlations between satellite elevation angle and Pseudo-Range Correction (PRC) through extensive tests. As a result, better PRC values were obtained by considering differences in satellite elevation angles at a reference site and the user location. We tested the model for a variety of baseline lengths greater than 250 km, and the positioning accuracy improved by 29–66% compared with traditional DGPS based on a single reference station. Positioning accuracies comparable to those of multi-reference DGPS were achieved in some cases.