The integration of the inertial navigation system (INS) and global navigation satellite system (GNSS) is suited for localisation and navigation applications, such as aircrafts, land vehicles and ships. The primary challenge is for navigation system to achieve accurate and reliable navigation solution during GNSS outages. This paper presents an observation prediction methodology for INS/GNSS bridging GNSS outages, which combines partial least squares regression (PLSR) and Gaussian process regression (GPR) to model the INS/GNSS observations and enable a Kalman filter to estimate INS errors. The performance of proposed PLSR/GPR prediction methodology was validated through four GNSS outages taken on flight experiment data, including diverse manoeuvre conditions. The experiment results demonstrate that remarkable performance enhancements are achieved through applying the proposed PLSR/GPR prediction methodology into INS/GNSS integration.

Retrospective analysis of the Total Loss and Serious Casualty Rate (TL/SC Rate) for UK registered deep-sea and inshore fishing vessels over a twenty-year period (1961–80) revealed a gradual and sustained increase.

The mean TL/SC rate for 1971–80 (6·041/1 000 vessels at risk) was almost 70 percent higher than the corresponding mean for the previous decade (3·79/1000 vessels at risk) and this difference was statistically significant (p < 0·05).

Subsequent examination of vessel losses and casualties by cause indicate that 64 per cent of this detected increase was due to a concomitant increase in vessels lost or damaged due to foundering (particularly inshore vessels) and that the mean vessel age at loss from this cause was 24 years old. Synthesis of available evidence relating to the onset of this increase (1971); mean age at loss due to foundering (24 years); and the current age structure of the fleet, supports the hypothesis that the increase in founderings in the early 1970s may be explained partly by a cohort effect resulting from the uncontrolled fleet rebuilding programme almost a quarter of a century earlier in the immediate post-war period.

Current combined risks of fishing vessel loss and casualty are about twice as great overall as those with which the Committee of Inquiry into Trawler Safety (1969) was concerned and over which it expressed deep concern.

Ionospheric disturbances affect Global Positioning System (GPS) performance in terms of accuracy and integrity, especially over the equatorial region. During the period of the disturbances, GPS receivers suffer from a high noise level. Not taken into account by the current stochastic model, the ionospheric disturbances degrade GPS positioning accuracy. In addition, non-Gaussian tails are observed in the distribution of the noise during the period of the disturbances; therefore the integrity of GPS can also be affected. This paper develops a statistical solution that is able to mitigate effects of ionospheric disturbances on GPS accuracy and integrity using a commercial dual frequency receiver. The Rate of Total Electron Content (TEC) change Index (ROTI), a parameter derived from the dual frequency receiver, is used to group the levels of ionospheric disturbances. The standard deviations of the pseudorange noise under different groups are evaluated. By incorporating both the ROTI and the satellite elevation, a modified stochastic model is proposed to reduce the effect of the disturbed observation on the positioning accuracy. The performance of the model is evaluated by a test and an inflated sigma for each group is recommended for over-bounding anomalies of observations to protect the user against threats from ionospheric disturbances. This technique, together with results in this paper, can be applied to mitigate the effects of ionospheric disturbances on GPS.

An approach formulated by vector algebra is proposed to deal with great circle sailing problems. Using the technique of the fixed coordinates system and relative longitude concept, derivations of formulae for this approach are simpler than those of the conventional methods. Due to fixing the initial great circle course, the great circle track (GCT) is determined. Since the course is fixed (known as “COFI” in this paper), the proposed approach, which we have named the “COFI method”, can directly calculate the waypoints along the GCT. It is considered that the COFI method is a more understandable and straightforward method to solve waypoint problems than older approaches in the literature. Based on the COFI method, a program has been developed for the navigator. In addition, the spherical triangle method with respect to the equator crossing point (STM-E) is developed by supplemental theorem. Several examples are demonstrated to validate the proposed COFI method and STM-E.

Studies have already been published on the probability of collision at sea, the effect of darkness and reduced visibility on the probability of collision, and on the distribution of collisions in particular areas. Only Minorsky and Comstock appear to have studied the extent of the resulting damage and sufficient data are not available for detailed analysis.

The establishment and operation of any traffic management system calls for a considerable outlay, so that an objective estimate of the extent of collision losses is often required. Such a cost/benefit survey was carried out by the Japan Transport Economics Research Centre on the assumption that a traffic management system can greatly reduce the incidence of collisions involving vessels of over 3000 g.r.t. Since half the aggregate loss is shown to relate to these large vessels (and considering their increasing capital value), an expenditure of ten billion yen or more (£20 million) over a period of ten years would appear to be cost effective if its primary purpose were to avert accidents to large vessels.

Recent studies confirm the importance of satellite positioning in location-based services (LBS) development. A field study was conducted in suburban and rural areas near Zagreb, Croatia in order to examine the real-time data compliance with recently established positioning performance requirements for LBS quality of service (QoS). Data analysis was based on comparison between actual positioning performance and pre-specified positioning parameter values using defined comparative procedures. The results presented here confirm a good correlation between the actual and required positioning performance, even without implementation of any of augmentation or assistance positioning methods.

This paper presents a robust train localisation system by fusing a Global Navigation Satellite System (GNSS) with an Inertial Navigation System (INS) in a tightly-coupled (TC) strategy. To improve navigation performance in GNSS partly blocked areas, an advanced map-matching (MM) measurement-augmented TC GNSS/INS method is proposed via an error-state unscented Kalman filter (UKF). The advanced MM generates a matched position using a one-step predicted position from a UKF time update step with binary search algorithm and a point–line projection algorithm. The matched position inputs as an additional measurement to fuse with the INS position to augment the degraded GNSS pseudorange measurement to optimise the state estimation in the UKF measurement update step. Both the real train test on the Qinghai–Tibet railway and the simulation were carried out and the results confirm that the proposed advanced MM measurement-augmented TC GNSS/INS with error-state UKF provides the best horizontal positioning accuracy of 0 ⋅ 67 m, which performs an improvement of about 71% and 90% with respect to TC GNSS/INS with only error-state UKF and only error-state Extended Kalman filter in GNSS partly blocked areas.

This paper is the fourth chapter of a series on Air Navigation Systems during theperiod from the early oceanic flights and the inception of commercial aviation to the introduction of INS in civil aircraft. Comments on the content of the paper would be welcomed by the author and the editor.

The accurate, continuous determination of position, heading and course at all times, under all normal operational conditions, would be very desirable. This ideal has not been achieved for flights or voyages of long duration, but the many developments of recent years begin to give some promise that it may be possible. For high altitude aircraft the continuous optical observation of celestial bodies offers an evident solution, and doppler systems can give continuous speed over ground. For ships, however, the attainment of such an ideal navigation system is difficult. The various shore-based radio navigation systems have made important contributions, as have the development of inertial techniques. In addition, automatic optical sextants have been developed which can be used in clear weather.

Eurofix is an integrated navigation system, which combines Differential GNSS and Loran-C. The Loran-C system is used to provide differential corrections for the GNSS pseudo-range measurements and integrity information by additionally modulating the transmitted signals. This modulation, however, is not allowed to degrade normal Loran-C operations. As data transmission is hindered by the aggressive Loran-C signal environment, special modulation patterns and Forward Error Correcting codes are designed to fulfil the requirements. Compared to other DGNSS services, Eurofix has a number of advantages: It covers a large area, its implementation in an already existing infrastructure is basically low-cost, it offers enhanced datalink availability in urban and mountainous environment, it has wide-area capabilities and, finally, it provides a free backup navigation system in case either Loran-C or GPS fails.

The paper describes the Eurofix system, focusing on the Loran-C data channel. A modified RTCM type-9 message format is used with special Forward Error Correction. At Delft University a real-life test set-up has been built to evaluate the Eurofix performance for different scenarios. The results on datalink and DGNSS performance are presented. It is shown that metre-level DGNSS performance is achievable with low bit rate data channels, using Loran-C stations at up to 1000 km distance.

The aim of this research was to clarify and quantify the demands of the working environment and watch-keeping regime for large commercial ships in relation to dark adaptation. The night lookout task requires the identification of the relatively bright navigational lights of other ships against the dark background of the sky and sea. The probability of detection is determined by the ambient lighting conditions on the bridge and the dark adapted state of vision. Light levels were such that threshold sensitivity (after 15 minutes) was reduced by around 2 log units in comparison to complete darkness. This has implications for the effective range of navigational lights at sea as defined in regulations. The intensity and position of navigation lights on larger vessels is such that the sensitivity of the eye under typical bridge conditions is likely to be sufficient for their visibility to be acceptable. This may not be the case for less well lit small craft.

GMDSS alerting was introduced in order to automate the call for search and rescue of a ship in distress, through the utilization of the most modern terrestrial and celestial communication systems. However, the GMDSS suffers from the inefficiencies associated with equipment design, operator competence and, most importantly, with those relevant to the equipment–operator interface. The GMDSS inefficiencies are frequently manifested in the form of false alerts, which apart from using resources, degrade the overall effectiveness of the SAR operation. In this paper, the GMDSS post-full-implementation record of false alerts received by the Greek MRCC is presented and analyzed. The observed persistence of high incidence of false alerts dictates the need for the proposal of further measures to combat false alerts, to promote the intended mission of the system and to generally improve the safety of navigation at sea.

The current positioning accuracy of the BeiDou Navigation Satellite System (BDS) Single Point Positioning (SPP) with code measurement is in the order of several metres due to systematic errors. To further reduce the systematic errors in SPP, this contribution develops a new strategy to BDS SPP with a sparse reference network, named Augmented SPP (A-SPP). In this method, the Combined Residual Errors (CRE) products of BDS B1I measurement are integrated with three optional base stations that are close to the rover station. Based on the Satellite Elevation Angle Weighted (SEAW) average technique, the code residual errors of each BDS satellite observed by the rover station can be acquired epoch-by-epoch. Finally, the corrected code observations for the rover station can be utilised to achieve an A-SPP solution. The validation of this method is confirmed by both static and kinematic tests. Results clearly show that the accuracies of the A-SPP solution for horizontal and vertical directions are better than 0·5 m and 1·0 m. This study suggests that the proposed A-SPP solution is a good option for single-frequency GNSS users to improve their positioning performance.

The aviation-shipping analogy cannot be used as an argument for a decrease in the need for maritime pilotage. The increasing complexity and upsizing of modern ships, in combination with a vast variety in ship types, economic maximisation, crewing and technical standards, lead to marginal ship operations that require specialist knowledge and skill. On the other hand, modern commercial aircraft have very standardised equipment and operating procedures and they approach and land at airports which also use standard radio-navigation aids and procedures.

Current Motion Compensation (MOCO) methods using Inertial Navigation System (INS)/Global Positioning System (GPS) integrated systems have provided an important advance in Synthetic Aperture Radar (SAR) imagery, but most of these methods only work well over a short imaging period. With the development of high-resolution SAR that provides image gathering over long periods, the need for higher levels of INS/GPS performance than normally available is desired. The higher requirement of INS/GPS for SAR MOCO is two-fold: (1) the accurate knowledge of location information, and (2) the smoothness of relative change in navigation error. In this paper, we design an INS/GPS architecture with dual-filter correction to obtain accurate absolute velocity and position measurement information with smooth low relative error noise over a long image gathering period. Real SAR data experimental results show that the proposed method effectively improves the MOCO performance of INS/GPS with long SAR imaging periods, in which the SAR azimuth resolution reaches 1·45 m, which is very close to the design value of 1 m.

The standards for CSTDMA Class B AIS will shortly be published by the International Electrotechnical Commission and equipment will become available during 2006. The perceived benefits that Class B brings to leisure craft users and its relatively low cost will make it attractive in the market place. A rapid take-up of Class B use can therefore be expected. This paper considers the impact that increased use of Class B will have on users of Class A AIS that are compulsorily fitted to larger vessels to meet the requirements of the International Maritime Organization Safety of Life at Sea convention. The CSTDMA Class B system has been designed to prevent overloading of the AIS VHF data link. This is briefly reviewed but there are a number of other aspects that need to be considered. These include: the increased garbling of Class B messages compared to those of Class A; the problems accruing from the low update rate of Class B information; the increase in display information that will need to be managed; and the possible increase in inappropriate manoeuvres of leisure craft caused by misplaced reliance on AIS. As a result of the investigation the paper highlights the fact that Class B users must not assume that their own presence, in the form of Class B transmissions, will be particularly visible on the bridge of many SOLAS vessels. This will continue to be the case for many years into the future, until such vessels are mandated to carry radar with AIS target overlay capability.

The Global Positioning System (GPS) can be employed as a free attitude determination interferometer when carrier phase measurements are utilized. Conventional approaches for the baseline vectors are essentially based on the least-squares or Kalman filtering methods. The raw attitude solutions are inherently noisy if the solutions of baseline vectors are obtained based on the least-squares method. The Kalman filter attempts to minimize the error variance of the estimation errors and will provide the optimal result while it is required that the complete a priori knowledge of both the process noise and measurement noise covariance matrices are available. In this article, a neural network state estimator, which replaces the Kalman filter, will be incorporated into the attitude determination mechanism for estimating the attitude angles from the noisy raw attitude solutions. Employing the neural network estimator improves robustness compared to the Kalman filtering method when uncertainty in noise statistical knowledge exists. Simulation is conducted and a comparative evaluation based on the neural network estimator and Kalman filter is provided.

In Satellite-Based Augmentation Systems (SBAS), the correction messages are transmitted to the users' receivers via geostationary communication satellites (GEOS) at GPS L1 (1575·42 MHz) frequency. Severe scintillations in the equatorial zone disrupt geostationary satellite links even at L-band. Observations of scintillations at 1·5 GHz from Calcutta (22·58°N, 88·38°E geographic, 32°N magnetic dip), located near the crest of the equatorial anomaly in the Indian zone, show that scintillations occur in patches of duration varying from a few minutes to several hours. During the solar maximum years 1998–2000, severe scintillations (Scintillation Index [ges ]15 dB) were recorded for 48 hr 55 min (1·27%) out of the total observation time of 3868 hr 9 min in the local time interval 19 to 00 hrs. In order to have a fail-safe system, it is suggested that more than one geostationary satellite be used in SBAS so that, if one link is disrupted, the other can be used for transmission of correction messages to the GPS users. The minimum longitudinal separation between two GEOS required for reliable operation of SBAS has been estimated, from the cumulative distribution of scintillation patch duration, to be 57° in the Indian longitude zone.

Classically difficult positioning environments often call for augmentation technology to assist the GPS, or more generally the Global Navigation Satellite System (GNSS) technology. The “Locata” ground-based ranging technology offers augmentation, and even replacement, to GPS in such environments. However, like any other system relying on wireless technology, a Locata positioning network also faces issues in the presence of RF interference (RFI). This problem is magnified due to the fact that Locata operates in the licence-free 2·4 GHz Industrial, Scientific and Medical (ISM) band. The licence-free nature of this band attracts a much larger number of devices using a wider range of signal types than for licensed bands, resulting in elevation of the noise floor. Also, harmonics from out-of-band signals can act as potential interferers. WiFi devices operating in this band have been identified as the most likely potential interferer, due partially to their use of the whole ISM band, but also because Locata applications often also may use a wireless network. This paper evaluates the performance of Locata in the presence of both narrow- and wide-band interfering signals. Effects of received interference on both raw measurements and final solutions are reported and analysed. Test results show that Locata performance degrades in the presence of received interference. It is also identified that high levels of received interference can affect Locata carriers even if the interference is not in co-frequency situation with the affected carrier. Finally, Locata characteristics have been identified which can be exploited to mitigate RFI issues.

The discussion following Captain C. V. Sølver's claim to have discovered an early Norse bearing-dial incidentally raised the question of what was the ‘dyoll’ referred to in English ship inventories of the fifteenth century. There are various practical reasons for doubting the theory that it was a compass-dial, that is to say a sun-dial with an inset compass, which for a particular latitude would, when correctly orientated, indicate the time of day. However, the idea that the ‘dyoll’ indicated time rather than direction seems to fit the evidence, and G. P. B. Naish's note on fifteenth- to seventeenth-century ship inventories leaves little doubt that it was an instrument for measuring equal intervals of time, and probably a sand-glass. This conclusion, which to some extent casts the early history of the compass card once more into the melting-pot, prompts a number of questions. Some are stated here and are answered either wholly or in part. Others remain to be answered.