Efficient and precise geolocation can be achieved by integrating a ranging system, such as GPS, with inertial sensors in order to bridge short outages, enhance accuracy degradation, and increase the temporal resolution in the ranging system. Optimal integration depends on appropriate filter methods that can accommodate the particular short-term dynamics experienced by platforms, such as UXO ground-based detection systems. The traditional extended Kalman filter was designed to integrate data from a linearized system excited by Gaussian noise. We compared this filter to modern filters that obviate these prerequisites, including the unscented Kalman filter, the particle filter, and adaptive variations thereof, using simulated IMU/ranging systems that follow a typical trajectory with both straight and curved segments. The unscented filter performed significantly better than the extended Kalman filter, particularly over the curved segments, yielding up to 50% improvement in the position accuracy using medium-grade inertial measurement units. Similar improvement was obtained for the unscented particle filter, and its adaptive variant, over the unscented Kalman filter (which performed comparably to the extended Kalman filter) when the statistical distribution of the IMU noise was non-symmetric (i.e., essentially non-Gaussian). While the few-centimetre geolocation accuracy goal for highly dynamic UXO characterization applications remains a challenge if tactical grade IMUs are integrated with a significantly degraded ranging system, using filters appropriate to the inherent nonlinear dynamics and potential non-Gaussian nature of the sensor noise tend to reduce overall errors compared to the traditional filter.

It is now widely recognised that a paradigm shift in air traffic control concepts is needed. This requires state-of-the-art innovative technologies, making much better use of the information in the air traffic management (ATM) system. These paradigm shifts go under the names of NextGen in the USA and SESAR in Europe, which inter alia will make dramatic changes to the nature of airport operations. A vital part of moving from an existing system to a new paradigm is the operational implications of the transition process. There would be business incentives for early aircraft fitment, it is generally safer to introduce new technologies gradually, and researchers are already proposing potential transition steps to the new system. Simple queuing theory models are used to establish rough quantitative estimates of the impact of the transition to a more efficient time-based – four-dimensional (4D) – navigational and ATM system. Such models are approximate, but they do offer insight into the broad implications of system change and its significant features. 4D-equipped aircraft in essence have a contract with the airport runway – they would be required to turn up at a very precise time – and, in return, they would get priority over any other aircraft waiting for use of the runway. The main operational feature examined here is the queuing delays affecting non-4D-equipped arrivals. These get a reasonable service if the proportion of 4D-equipped aircraft is low, but this can deteriorate markedly for high proportions, and be economically unviable. Preventative measures would be to limit the additional growth of 4D-equipped flights and/or to modify their contracts to provide sufficient space for the non-4D-equipped flights to operate without excessive delays. There is a potential for non-Poisson models, for which there is little in the literature, and for more complex models, e.g. grouping a succession of 4D-equipped aircraft as a batch.

Versions of this paper were first presented at the Royal Institute of Navigation GNSS Vulnerabilities and Solutions Conference held at Baska, Croatia in September 2008 and the Royal Institute of Navigation NAV 08 Conference held at Church House, Westminster, London in October 2008.

The US Global Positioning System (GPS) is currently the primary source of Position, Navigation and Timing (PNT) information in maritime applications, whether stand-alone or augmented with additional systems. This situation will continue in the future with GPS, possibly together with other Global Navigation Satellite Systems (GNSS) e.g. Galileo, being the core PNT technology for e-Navigation – the future digital maritime architecture. GPS signals, measured at the surface on the Earth, are very weak. As such, the system is vulnerable to unintentional interference and jamming, resulting in possible denial of service over large geographical areas. The result of such interference could be the complete failure of the mariner's GPS receiver or, possibly worse, the presentation to the mariner of hazardously misleading information (HMI) for navigation and situational awareness, depending on how the GPS receiver reacts to the jamming incident. Recognising this, the General Lighthouse Authorities of the United Kingdom and Ireland (GLA), in collaboration with the UK Ministry of Defence (MOD) Defence Science and Technology Laboratory (DSTL), have conducted a series of sea-trials with the aim of identifying the full effects of GPS jamming on safe navigation at sea.

This paper presents the key findings of these trials and provides important information on the effect of GPS denial. The GLA are playing a pivotal role in the establishment of eLoran as an independent source of PNT, taking advantage of eLoran's complementary nature, having dissimilar failure modes to GPS and the future GNSS. This paper provides information on the performance of an eLoran receiver in an area of GPS service denial. The paper presents the rationale for the work, details the system architecture employed, the data gathering efforts and finally the data analysis procedures, results and conclusions.

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.

Application of map-matching techniques to GPS positions can provide accurate vehicle location information in challenging situations. The Hidden Markov Model (HMM) is a statistical model that is well known for providing solutions to temporal recognition applications such as text and speech recognition. This paper introduces a novel map-matching algorithm based on HMM for GPS-based wheelchair navigation. Given GPS positions, a hidden Markov chain model is established by using both geometric data and the topology of sidewalk segments. The map-matching algorithm employs the Viterbi algorithm to estimate correct sidewalk segments as hidden states in a HMM in order to match GPS trajectory on the corresponding segment sequence. The HMM-based map-matching algorithm was validated on a campus sidewalk network for wheelchair navigation. The results show an improvement in tracking a wheelchair in dense urban conditions both in accuracy and in computational time.

A version of this paper was first presented at the Royal Institute of Navigation NAV 08 Conference held at Church House, Westminster, London in October 2008.

The North Sea oil platforms are reliant on regular and reliable helicopter operations for the movement of staff and supplies. The environment is challenging and there have been six fatal accidents incurring the loss of 79 lives since the mid-1970s. The need for accurate and reliable helicopter approach procedures has been identified and this paper reports the results of a feasibility study into the use of EGNOS-based approaches to oil platforms in the North Sea.

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.

Knowing what information, and from which sensory cues, is available to an animal regarding its position and direction of movement is vital for unravelling the mechanisms underlying animal navigation. Although considerable progress has been made with traditional field and laboratory techniques, these approaches generally do not provide direct control over the animal's motivation to display its sensory abilities. In contrast, psychologists have for many decades used conditioning as a reliable tool to study sensory perception as well as the mechanisms underlying learning. There has been growing interest in the use of conditioning techniques to investigate responses to stimuli that might be used in guiding movement over long distances. This review seeks to facilitate that development by providing a general introduction to conditioning and the considerations involved in designing robust conditioning experiments together with a perspective for its future use in studying sensory systems in migratory and homing species.

The Automatic Identification System (AIS) has proven itself to be a valuable source for ship traffic information. Its introduction has reversed the previous situation with scarcity of precise data from ship traffic and has instead posed the reverse challenge of coping with an overabundance of data. The number of time-series available for ship traffic and manoeuvring analysis has increased from tens, or hundreds, to several thousands. Sifting through these data manually, either to find the salient features of traffic, or to provide statistical distributions of decision variables is an extremely time consuming procedure. In this paper we present the results of applying computer vision techniques to this problem and show how it is possible to automatically separate AIS data in order to obtain traffic statistics and prevailing features down to the scale of individual manoeuvres and how this procedure enables the production of a simplified ship traffic model.

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.

A version of this paper was first presented at the Royal Institute of Navigation NAV 08 Conference held at Church House, Westminster, London in October 2008.

SESAR is Europe's ‘Single European Sky Air traffic Research system’, targeted at post-2020. The vision is to integrate and implement new technologies to improve air traffic management (ATM) performance. The focus for planning and executing system operations will increasingly be aircraft navigating high-quality 4D trajectories: a 4D trajectory is the aircraft path, three space dimensions plus time, from gate-to-gate, i.e. including the path along the ground at the airport. A 20+year ATM plan has to use limited information on the success of innovations and the development of large-scale, often safety critical, software, which by its nature can take markedly longer and cost markedly more than early estimates. SESAR must be sufficiently flexible in deployment to maximise financial benefits to individual stakeholders using their specific financial criteria. Airline needs are the main ATM system/business drivers. Airlines do not want to commit to developing an ‘ultra-modern system’ per se, but rather to one that makes business-sensible investments in new technologies that are indispensable for achieving improved safety and meeting projected capacity requirements. The approach has been to use simple corporate finance ideas to examine the different viewpoints and business environments of air traffic service suppliers (ANSPs) and individual airlines. The key decision-making point is that ANSPs act as an agent for airlines as a whole. The key financial point is that a typical airline has to work hard to survive and needs quick paybacks on investment. The design of the SESAR R&D and project portfolios can learn lessons from information technology systems design and deployment. ‘Real option analysis’ of systems can increase business value by improving the sequencing and partitioning of projects, helping to ensure that the system is adaptable to technological innovation and changes in business needs.

This paper describes the verification of a real-time attitude determination algorithm during GPS attitude receiver hardware development. The GPS attitude receiver of 24 channels had been already developed in Surrey University. However 24 channels were not enough for practical usage. For this reason, a 48-channel attitude receiver with 12 channels for each antenna has been developed. To estimate attitude in real time, precise relative positions of the GPS antenna array have to be determined as rapidly as possible. However, the calculation load based on the conventional algorithm is too burdensome to perform using the RISC microprocessor. Therefore, in this paper, the cycle ambiguities of each base vector are resolved using SNUGLAD (Seoul Nat Univ GNSS Lab Attitude Determination), the design focus of which is to allow the receiver to estimate the 10 Hz onboard solutions. To keep precise solutions continuously, after ambiguity removal, cycle slip must be detected or isolated. Otherwise, the receiver would output erroneous solutions after a short signal blockage or fading of the GPS signal. To prevent this, we defined the cycle slip detection and repair scheme using a standard extended Kalman filter, which can detect and repair cycle slip within one cycle. As a result, this paper shows that time synchronized measurement with good quality and a reliable solution can be provided by the hardware developed with inexpensive chipsets and that this may be a possible cost efficient sensor for UAV or microsatellites.

This year celebrates the 90th anniversary of the historic first Atlantic crossing by Alcock and Brown in their Vickers aircraft. This paper draws on the log, chart, notes and equipment held in the RAF Museum at Hendon and Sir Arthur Brown's own words to tell the story of the crossing.

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.

In this study, a real time maritime traffic support model is developed for safe navigation in the Strait of Istanbul, also known as the Bosporus. The present model simulates vessel trajectories corresponding to possible headings, using channel geometry, counter traffic, and surface currents as input. A new MATLAB code is developed for the simulation and the Marine GNC Toolbox (Fossen and Perez, 2004) is used for the vessel hydrodynamics and the auto-pilot model. After computing the trajectory tree of the vessel by forward-mapping its position distribution with respect to the initial position vector, the casualty probabilities of each trajectory are found. Within certain restrictions on vessel geometry, the proposed model predicts the safest possible intended course for the transit vessels based on the navigational parameters including position, speed, and course of the vessel. The model is tested for the Strait of Istanbul for validation. Without loss of generality, the model can be used for any narrow channel with a vessel traffic system providing the necessary input.

A version of this paper was first presented at the Royal Institute of Navigation NAV 08 Conference held at Church House, Westminster, London in October 2008.

There exist various applications for indoor positioning, amongst which indoor positioning and tracking in urban environments has gained significant attention. Some user communities, like fire fighters, ideally require indoor accuracy of less than one metre, with accuracies of less than six metres acceptable by some other user communities. Achieving this level of accuracy requires a detailed profiling of error sources so that they can be better understood so that, in turn, indoor positioning accuracy in the presence of these errors can be further improved. Some well known error sources like multipath, NLOS (non line of sight), oscillator drift, dilution of precision and others have been studied and can be found in the literature. A less well known error source that can substantially affect indoor positioning accuracy are the effects of the dielectric properties of building materials on propagation delay.

Various RF and non-RF based prototypes that claim to be suitable for indoor positioning can be found in the literature. Most of the existing literature discusses algorithms and summarizes the positioning results that were achieved during field tests using a prototype system or, more commonly, simulations. Little of this existing literature provides a breakdown of the total navigation system errors observed with the objective of analyzing the contribution of each error source independently.

The paper will first provide a brief overview of the precision personnel locator system developed at the Worcester Polytechnic Institute. The field tests and observed indoor positioning results using this RF prototype will then be summarized and used to provide a baseline to establish a system error budget. The total observed error will be broken down and a detailed analysis of each of the error sources will be presented based on actual measured data in a variety of indoor environments. This leads to a better understanding of how each error source affects indoor positioning accuracy. Each of the error sources can then be independently optimized to minimize the observed errors. Specifically, the interplay between the dielectric properties and multipath profiles will be highlighted. This paper will conclude by presenting an error budget which can be used as a practical lower bound when designing precise indoor positioning systems.

Global Navigation Satellite System (GNSS) Receiver Autonomous Integrity Monitoring (RAIM) is essential for safety-of-life and liability critical applications. This paper discusses two fundamentally different ways to assess the integrity risk of an operation with RAIM, based on a different amount of information available: the expected (or average) performance that is computed using the GNSS models only and the real-time (or actual) performance, which also uses information on the internal status of a GNSS receiver. It is shown both theoretically and by simulation that the real-time integrity risk significantly exceeds the expected risk after the detection and exclusion of a failing satellite. Therefore, while most published RAIM algorithms base their performance assessment on the expected performance only, this is only correct when the requirements allow the risk evaluation to be averaged over multiple operations. However, when the GNSS integrity requirement is to be applied on a ‘per operation’ basis, real-time integrity measures are more appropriate.

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.

This study of Columbus' navigation is unique because it was written by an historian who is also a trained and experienced professional global (and ocean) navigator, rather than an academic historian with only superficial knowledge of the science of navigation as practiced by Columbus and other early navigators. The study is also unique in that as an American historian author disagrees with his colleagues in the USA who present the “politically correct” view of Columbus as an unskilled entrepreneur who obtained his limited knowledge of navigation as a crew member or passenger on Portuguese voyages, rather than as one of the most skilled and experienced of the cadre of respected Genoese captains and navigators used by kings throughout Europe to perform their maritime enterprises.

This paper studies the effectiveness of a ship's tunnel bow thruster with slow speed ahead. After describing the general reasons for the decrease of performance with slow speed ahead, the Anti Suction Tunnel (AST) is analyzed as an advisable state-of-the art design option that aims to improve performance.