The weak GPS signal-processing work described here was part of the development of an innovative GPS tag – TrackTag™. The technology is aimed at animal tagging applications and therefore has particular challenges. These primarily relate to designing a tag to be small enough in physical size and weight so as not to impact the behaviour of the animal under study as well as robust enough to operate wherever the animal goes. TrackTag's architecture differs from that of a conventional GPS receiver. The key differences are that very short (typically 24 ms) snapshots are used and there is no processing intelligence on the tag itself. Such a short length of ON time, with no need for longer warm or cold starts, results in very little energy being used. This, in turn, allows the design of the tag to be made very small with a minimal battery size requirement and capable of being used over far greater periods than conventional GPS tags. Processing of the data is done on a PC following the download of the tag's memory.

The GPS signal-processing using such short snapshots must not compromise the accuracy of the positions calculated and they should be comparable or better than normal GPS receivers. Weak signal processing is also a requirement for tracking signals in harsh environments involved with tagging animals in their natural habitat. This research has demonstrated that weak-signal processing coupled with the short snapshots, and careful integration of a suitable antenna, allows tracking under rainforest canopy and marine environments. Conventional GPS tends not to work well under those conditions.

The detection of flying targets in the night sky has provided interest for bird migration research over many years with methods largely dependent on moon watching or the use of radar and infrared camera. These methods lack the versatility of the system described in this paper which detects and automatically records aerial targets in the night sky of a size greater than 5 cm and at a distance of 100 to 1000 metres from the observer. The principle design features are first, an optical device for receiving images of targets on two high-sensitivity CCD matrices when illuminated by white light from searchlight beams and secondly, instantaneous parallactic electronic computation enabling the distance from device to target to be accurately measured, and sequential images of each target to be recorded to computer. The device has been tested on targets during the main seasonal nocturnal migration of birds and provides accurate image details of important target flight parameters including: altitude, linear size (wing span and body length), direction of flight (ground track), orientation of the body axis – heading, ground speed, wing-beat frequency, number of wing-beats in each series of beats, duration of the pause between each series of wing-beats, and type of flight trajectory. There are also the potential practical applications for aviation bird-strike at night as well as the remote monitoring of insects, bats and other targets of natural and artificial origin.

During group navigation the information shared by group members may be complex, heterogeneous and may vary over time. Nevertheless, modelling approaches have demonstrated that even relatively simple interactions between individuals can produce complex collective outcomes. In such models each individual follows the same simple set of local rules, giving rise to differential outcomes of the navigational decision-making process depending on various parameters. However, inherent heterogeneity within groups means that some group members may emerge as more influential than others in navigational tasks and this underlying social structure may affect the ability of the group at large. Here, we present our preliminary modelling of group navigation specifically developed to include internal group structure. Building on existing models and recent experimental results we examine the role of individual influence on group navigation and its effects on group navigational ability.

The paper pertains to the reduction of measurement errors in gyroscopes used for tracking the position of walking persons. Such tracking systems commonly use inertial or other means to measure distance travelled, and one or more gyros to measure changes in heading. MEMS-type gyros or IMUs are best suited for this task because of their small size and low weight. However, these gyros have large drift rates and can be sensitive to accelerations. The Heuristic Drift Reduction (HDR) method presented in this paper estimates the drift component and eliminates it, reducing heading errors by almost one order of magnitude.

Managing the transit vessel traffic in the Strait of Istanbul is a highly complex operation since vessels, weather and water conditions, and a set of regulations affect its operation significantly. At the present time, the Vessel Traffic Services (VTS) operators manage the traffic based on some fundamental rules. After discussions with the VTS, in this report, we present a mathematical formulation of the scheduling process currently in place and validate it by comparing its results with scheduling decisions made by the operators in some days of 2005. The results are highly promising. The fundamental philosophy of the algorithm is to schedule the vessels with highest waiting time first while giving priority to large vessels carrying dangerous cargo. Our goal has been to incorporate the algorithm into a simulation model designed to be used for risk analysis purposes. The proposed algorithm can be slightly altered and used for traffic scheduling in other waterways as well.

The paper addresses the issue of planning emergency manoeuvres and re-planning ship trajectories in case of unpredicted target behaviour. It introduces two methods. The first is responsible for monitoring other ships parameters, estimating the probability of illegal target behaviour and re-planning own trajectory in case of unpredicted events. The second is a visualization tool that enables the navigator to assess collision risk in an encounter situation and choose a collision avoidance manoeuvre if necessary. This tool is based on the Collision Threat Parameters Area display and offers new features: fuzzy sectors of forbidden speed and course values and the possibility to use any given ship domain. Both methods are fast enough to be applied in the real-time decision-support system.

One of the basic tasks in shipping is to ensure safe navigation of vessels. The concept of the ship domain is of major importance in the assessment of a navigational situation and the avoidance of ship collisions. It is difficult to determine a ship domain as its shape and size depend on a number of factors. One question to be answered before the determination of the ship domain is which method to use: statistical, analytic, or expert method using artificial intelligence tools; other questions are connected with domain interpretation. The authors have analyzed the ship domain as a criterion for the assessment of ship navigational safety in an encounter situation in the open sea. The research results are used to answer some of the questions.

Part 2 includes definitions of the ship domain and ship fuzzy domain. Part 3, in turn, presents methods of their determination as well as relevant questions. The results of the authors' research, described in Part 4, make up a basis for the determination of the domain and ship fuzzy domain. These have been determined with the so-called dynamic domains as a point of departure. The criteria of ship domain and closest point of approach are compared and discussed. Encounters of various size ships are considered in Part 5. The research and its results are described. Both ship domains and ship fuzzy domains of encountering ships are analyzed. Then, conclusions have been formulated in relation to the effect of the sizes of encountering ships on the shapes and sizes of their domains. Final conclusions are given in Part 6.

Armed with the axiom that the best way to avoid collision at sea is for one ship to pass under the stern of the other, this paper revisits the early steering and sailing rules. It conjectures that the port tack rule was an antidote to the sailing ship's imperative to gain ground to windward even at the cost of risk of collision. It draws attention to evidence that with early steamships, free of the port tack rule, one altered course to pass astern of the other and that, in fact, the one to alter was invariably the faster of the two. It traces, to the want of prescribed navigation lights, the introduction of the port helm/right rudder rule for all ships by day and by night. It records how with the introduction of prescribed lights the port tack rule, though in a form proposed by France, was re-introduced for sailing ships together with an analogous crossing rule for streamers. The paper concludes that the port tack rule is redundant in this collision conscious age and that its objective of motivating one ship to alter course can be achieved by making both ships to blame in the event of a collision. It is submitted that these lessons offer the e-navigator a method of avoiding collision at sea applicable in all situations; the only technical requirement for its safe conduct is for each ship to be able to tell instantly and accurately at any moment how the other ship is heading.

The ranging accuracy provided by pseudorange-only techniques is usually no better than a few metres when no differential corrections are applied. Carrier-phase algorithms, on the other hand, yield higher-precision estimates – down to a few millimetres – but are prone to ambiguities difficult to resolve. An easier-to-implement method, using single-frequency pseudorange measurements only, is presented. It allows for a decimetre-level relative positioning accuracy. Results, derived from the GPS Relative Positioning Equations, are validated with actual satellite data from the Gravity Recovery and Climate Experiment (GRACE) mission.

The new millennium brought an asymptotic interest in space technology. Besides existing operational global positioning systems i.e. GPS and GLONASS, another two have already emerged: GALILEO and Compass/Beidou. Alternatives to GPS imposed the GNSS concept, which has crystallized in a short time. The true reasoning of this excessive need for positioning information is beyond the scope of this paper; instead, an analysis of orbital behaviour of GPS, GLONASS and GALILEO is conducted. GNSS orbits have similar characteristics permitting us to encompass them under the term Medium Earth Orbits (MEO). However, small differences between mean orbital elements of the three systems produce a significantly different reaction of their satellites' orbits to the natural perturbing factors. This study analyzes the three space segment characteristics, introduces the analytical method used to evaluate variations of orbital elements under the most significant perturbing influences and offers a broad comparative image of the dynamic behaviour of the three GNSS constellations.

Ambiguity resolution is essential for precise range determination. As it is difficult to process, a good ionospheric model is essential to get unambiguous results or to reduce time to solve the ambiguities. In this paper, a developed model to determine the differential ionospheric error to sub-centimetre accuracy is described. As a function of elevation angle and TEC, the model is applicable at any location and only requires a single frequency receiver provided the TEC over the reference station is known. It has been evaluated using real GPS measurements at spaced stations in Glasgow (UK) and Stirling (UK), where the results showed good correlation. It was found that the variance ratio and reference variance of the ambiguity resolution rate and the quality of the differential positioning solution are improved. Significant improvements of more than 50% have also been found by correcting the differential ionospheric delay in the measurements for the estimated positions.