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.

The literature of the recent past concerned with the collision avoidance regulations cannot be regarded as the model of rational scientific discussion. Subjective arguments based on personal experience of particular situations and very general mathematical analyses are pitted together without any generally accepted criteria by which to judge them. Obviously both mathematics and experience have great relevance to this geometrically simple, but operationally involved, problem. One step nearer a rational optimization of a set of regulations defining action during collision avoidance would be a formalization of the criteria a successful rule of the road must meet, and of the operational difficulties it faces. The present regulations, for instance, suffer from several logical inconsistencies which are difficult to describe in simple mathematical terms.

This paper presents the results of an experiment to investigate the impact of helicopter rotor blades on GPS signal reception. An offshore transport helicopter was equipped with a measurement system including a TSO-C129 compliant receiver and a custom research receiver. GPS signals passing through rotor discs of this aircraft were found to suffer a reduction in received signal strength, leading to potential navigation and RAIM availability concerns. The phenomenon will vary between installations and receiver types. Test procedures to identify the occurrence of the phenomenon in operational GPS installations are presented, together with possible in-service monitoring programs to assess the impact on the navigation function.

We develop a new frequency-domain dynamic response method to model integrated Inertial Navigation System (INS) and Global Positioning System (GPS) architectures and provide an accurate impulse-response-based INS-only navigation solution when GPS signals are denied (GPS outages). The input to such a dynamic system is the INS-only solution and the output is the INS/GPS integration solution; both are used to derive the transfer function of the dynamic system using Least Squares Frequency Transform (LSFT). The discrete Inverse Least Squares Frequency Transform (ILSFT) of the transfer function is applied to estimate the impulse response of the INS/GPS system in the time domain. It is shown that the long-term motion dynamics of a DQI-100 IMU/Trimble BD950 integrated system are recovered by 72%, 42%, 75%, and 40% for north and east velocities, and north and east positions respectively, when compared with the INS-only solution (prediction mode of the INS/GPS filter). A comparison between our impulse response model and the current state-of-the-art time-domain feed-forward neural network shows that the proposed frequency-dependent INS/GPS response model is superior to the neural network model by about 26% for 2D velocities and positions during GPS outages.

In 1991 Trimble Navigation introduced a Global Positioning System (Gps)-based attitude determination receiver capable of 3-axis solutions with accuracy to several milliradians for airborne, sea and land platforms. This paper discusses the physical, architectural, and operational features of this receiver system. Analysis of system performance will also be reviewed for various configurations and user applications. The Trimble Navigation attitude determination receiver uses differential carrier phase techniques to determine azimuth, pitch and roll angles of a 3-antenna array. This product is designed to operate in a variety of user applications and to withstand rugged operating environments. Trimble Navigation has expanded its proven GPS sensor architecture to incorporate three independent RF sections and additional processing channels to measure and process the differential phase between antennas on two orthogonal baselines. Direct measurement of differential phase utilizing a common local oscillator provides highly accurate relative phase data. The navigation and attitude processor computes azimuth, pitch, and roll angles as well as position, velocity and time. The solution accuracy and stability statistics are sensitive to various parameters. Antenna baseline length, signal multipath, platform dynamics and filtering are investigated. Test data from static and various dynamic platforms are also presented.

Every day several hundred subsonic aircraft travel between the European and North American continents. Because of noise limitations at major airports, aircraft turn-around times and the time difference between the continents, the direction of the main traffic flow changes through the day. In the afternoon (GMT) the flow is predominantly westbound, while in the early hours of the morning the flow is predominantly eastbound. Oceanic air traffic control for the North Atlantic region has evolved into what is now known as the Organized Track System; traffic is divided into streams, each stream flying at a specified set of flight levels on one of several adjacent tracks. Figure 1 shows an example of the subsonic track system during the westbound peak. To secure operating economy the layout of the track system on any day is matched to the pattern of the upper winds.

The paper is mainly concerned with the principles used by TCAS (Traffic alert and Collision Avoidance System) to resolve conflicts between airborne aircraft. It leans heavily on an earlier paper which describes the threat-detection process. The simulation results given were obtained using a fast-time computer model for random traffic and comprise statistics on miss distance, warning time, etc., for a simple traffic pattern.

This paper develops a method for the prediction of wave height, period and direction on a 200-mile grid over the North Atlantic Ocean, using a wave spectrum technique. The method could be useful in conjunction with optimum ship routing across the ocean.

AS discussed recently by Hanssen and James, ship routing across the ocean, using the optimum route with respect to weather conditions, is now becoming a practical possibility. One essential requirement is to predict the wave heights and lengths over all parts of the area concerned. This would require first, of course, a forecast of the wind conditions. At present the Meteorological Office issues prognostic weather charts 24 hours ahead and wave predictions must be tied to them. Wave conditions are not determined instantaneously by the weather conditions at a given time, but tend to be an integration of the weather conditions over two, three, or even more days before and so wave predictions 24 hours ahead are likely to be more accurate than the wind forecasts.

Because GPS is a radio navigation system which has a very low power level, it is vulnerable to RFI. Excessive RFI could cause receiver performance degradation, such as degradation of position accuracy, loss of lock and increased acquisition time. After GPS modernization plans introduce dual-frequency civil signals to mitigate ionospheric errors, RFI will remain as one of the dominant threats for differential GPS navigation systems. Examples of safety-critical civil aviation and military missions threatened by RFI include the Local Area Augmentation System (LAAS) and the Joint Precision Approach and Landing System (JPALS). This paper focuses on RFI mitigation through integrity monitoring for a DGPS system like LAAS or JPALS. The mitigation strategy consists of two parts. First, the paper develops a new RFI detection method, using a raw divergence statistic. Second, the paper investigates strategies for maintaining integrity in the case that RFI is detected.

To validate the utility of the divergence-based RFI monitor, this paper takes an experimental approach. The experiments assess the performance of the divergence metric and compare it to existing alternatives for RFI detection, such as metrics for Automatic Gain Control (AGC) and carrier-to-noise ratio (C/N0). Generating a monitoring threshold for these statistics proves challenging, because the threshold depends both on the type of RFI threat (e.g. continuous wave, narrow band, wideband, pulsed) and on environmental conditions, such as temperature. As experiments illustrate, the divergence statistic resolves these limitations, as divergence directly estimates ranging source error, independent of the type of RFI threat or the environmental conditions.

GPS receivers have been used successfully on low Earth orbit (LEO) satellite missions for several years. The use of a GPS receiver at altitudes higher than LEO, however, is non-trivial as the receiver will be outside the main lobe of the GPS broadcast signals, and it will have to track signals from GPS satellites transmitting from the other side of the Earth. This paper will review the special hardware and software adaptations required for GPS receiver operations on a medium Earth orbit or geostationary satellite, along with preliminary results from simulations and an in-orbit experiment.

The rates of collision and stranding at sea are very high. The primary causes of stranding are: not checking a ship's position, inadequate route planning, operational misjudgement and inefficient watchkeeping. These causes are responsible for 90 percent of strandings according to accident statistics. Reduction in stranding risk would be of considerable economic benefit and would also reduce pollution and be welcomed by shipping companies and, of course, by crews.

We have developed a local-area ionospheric time-delay model that consists of nominal and perturbation models. The nominal model describes the trends of ionospheric time delay over 1–2 days and uses nine parameters. The perturbation model describes rapid changes of ionospheric time delay over 2–3 hours and uses six parameters. All the parameters are estimated from raw data measured at one reference station, which has filters to estimate all the parameters of the local-area ionospheric time-delay model. With this model and Black's tropospheric time-delay model, we obtain compensated Differential GPS (DGPS) pseudorange corrections by subtracting the atmospheric time-delay difference between the reference station and the user. We believed that the model could extend DGPS coverage. To check this, we analyzed experimental data. The results show that this algorithm not only improves DGPS positioning accuracy, but also extends DGPS coverage from 100 km to more than 400 km. We named this new algorithm the Seoul National University Differential GPS (SNUDGPS).

In 1952 the first transpolar flight by a commercial aircraft was carried out. During the six years that have since passed, S.A.S. aircraft have made 1635 flights across the arctic region representing approximately 26,000 flying hours. Our experience in polar navigation has been built up first on a large number of charter flights, then on regular flights on the sub-polar route to Los Angeles, and finally on regular flights across the Arctic Ocean to Japan.

In the Venus capture period, it is difficult for celestial autonomous navigation to satisfy the requirement of high precision. To improve autonomous navigation performance, a Direction, Distance and Velocity (DDV) measurements deeply integrated navigation method is proposed. The “deeply” integrated navigation reflects the fact that the direction and velocity measurements suppress the Doppler effects in the pulsar signals. In the pulsar observation period, the direction and velocity measurements are utilised to compensate for Doppler effects in the pulsar signals. By these means, the residual effects can be ignored. When the direction, distance or velocity measurements are obtained, they are fused to improve the navigation performance. Simulation results demonstrate that the DDV measurements deeply integrated navigation filter converges very well, and provides highly accurate position estimation without a high quality requirement on navigation sensors.

Spatial boundaries play an important role in defining spaces, structuring memory and supporting planning during navigation. Recent models of hierarchical route planning use boundaries to plan efficiently first across regions and then within regions. However, it remains unclear which structures (e.g. parks, rivers, major streets, etc.) will form salient boundaries in real-world cities. This study tested licensed London taxi drivers, who are unique in their ability to navigate London flexibly without physical navigation aids. They were asked to indicate streets they considered as boundaries for London districts or dividing areas. It was found that agreement on boundary streets varied considerably, from some boundaries providing almost no consensus to some boundaries consistently noted as boundaries. Examining the properties of the streets revealed that a key factor in the consistent boundaries was the near rectilinear nature of the designated region (e.g. Mayfair and Soho) and the distinctiveness of parks (e.g. Regent's Park). Surprisingly, the River Thames was not consistently considered as a boundary. These findings provide insight into types of environmental features that lead to the perception of explicit boundaries in large-scale urban space. Because route planning models assume that boundaries are used to segregate the space for efficient planning, these results help make predictions of the likely planning demands of different routes in such complex large-scale street networks. Such predictions could be used to highlight information used for navigation guidance applications to enable more efficient hierarchical planning and learning of large-scale environments.

Naval maritime operations entail a permanent concern for safety, ensuring that all crew members receive the necessary information on time. This implies the existence of specific training for improving non-technical skills (NTS). This paper proposes that bridge resource management (BRM) may be determinant for the success of naval maritime operations. Through a literature review on NTS, maritime team training and BRM, the paper presents insights about the way the level of NTS, inherent to BRM, may be determinant for naval officers to operate in safety. We propose that human error may be minimised and safety maximised in military teams operating in the maritime environment through the implementation of an NTS training programme. The paper offers an insight into the importance of safety during maritime operations, focusing on recent international orientations about training requirements, proposing that implementing BRM will be pivotal for the future of the military navy context.

This article presents efficient and practical methods for path planning of optimal interceptions on two-dimensional grids with obstacles, such as raster charts or non-distorted digital maps. The proposed methods search for optimal paths from sources to multiple moving-targets by a novel higher geometry wave propagation scheme in the grids, instead of the traditional vector scheme in the graphs. By introducing a time-matching scheme, the optimal interception paths from sources to all the moving-targets are obtained among the combinations with linear time and space complexities. Two optimal path planning methods for multiple one-to-one interceptions, the MIN-MAX and MIN-AVG, are applied to emulate the real routing.

This paper proposes an airborne transceiver system as an alternative navigation system and a triangulation method using bidirectional range measurements as a method of transceiver position determination. We suggest several system arrays that can estimate each mobile transceiver position in real time. We found that our suggested alternative navigation system working in a 700 km×900 km region is feasible using only 10 transceivers at an altitude of 42 km, furthermore its performance can compete with that of Galileo's Open Service. This paper will contribute to the establishment of an alternative or backup navigation system with modest expenditure and a short development period, and which is independent of GPS.

This paper traces the birth and formation of Vessel Traffic Services, examines the rapid growth of such schemes worldwide and notes the tendency for mandatory ship reporting systems to be operated from VTS centres. Questions are asked about this tendency and thoughts are provided.

The International Maritime Organisation (IMO), in its Sub-Committee for the Safety of Navigation, has recommended the acceptance of GPS as a component of the World-Wide Radionavigation System. However, the Sub-Committee highlighted that GPS accuracy is not sufficient for harbour entrances and approaches and that it does not provide instantaneous integrity to alert users of any malfunction. The Sub-Committee considered that DGPS could improve both the accuracy and the integrity of GPS. In practice, the use of differential corrections to GPS signals allows elimination of most of the errors of GPS and improves the integrity of the service significantly. While GPS does not provide instantaneous integrity, the use of DGPS reference stations, which continuously monitor the signals of the visible satellites, enables the timely warning (under 15 seconds) of any malfunction or failure. However, the recent discontinuation of Selective Availability (SA), which led to an improvement in stand-alone GPS accuracy, has changed some of the premises that justified differential services. This paper presents the needs of mariners in terms of radio positioning, with the aim of evaluating the ability of unaugmented GPS and DGPS to comply with marine navigation requirements. The impact of the removal of SA on DGPS and its benefits for mariners will also be discussed in order to show that DGPS is still adequate and useful for mariners.