Current strategic plans for Air Traffic Management (ATM) envisage a transition from radar control to a trajectory-based system. Part 1 sketched the historical origins of separation minima and then analysed the safety thinking behind current minima and the issues involved in risk modelling. Part 2 examines the future situation. This focuses on the intermediate steps to the final system – upgraded capabilities in a mixed-equipage system. Future traffic mixes two categories of traffic: V aircraft, i.e. vectored traditional ATC-handled, and 4D aircraft, i.e. flying on 4D trajectories. Conflict probe and other decision support tools will need to be in place, inter alia to prevent controller workload from increasing. Conceptually, future risks in the transition period will be the sum of three types of aircraft encounter risk: V/V, 4D/4D and 4D/V. These pose different kinds of problem for ATC, appropriate conflict alerting systems and risk assessment. The numbers of 4D/V encounters increase rapidly with growth in the proportion of 4D aircraft. With reduced minima, airborne collision avoidance systems would be unlikely to resolve higher relative velocity encounters were the ATC system to fail. It would be a difficult decision to reduce markedly ATC separation minima for any category of aircraft encounters during the transition period.

Every navigator is familiar with the necessity for correcting sextant observations of altitude for the effect of atmospheric refraction. He does this by means of tables which the great majority of navigators are compelled to take on trust, as they would a table of haversines. Unfortunately it is much easier to guarantee the accuracy of a table of a straightforward mathematical function than it is to tabulate accurately an optical effect occurring in a notoriously variable atmosphere. Recent American work based on large numbers of marine observations has to some extent called into question the accuracy of the low-altitude portions of the usual tables, and it therefore seems worth while to give a brief account of refraction theory and also to consider how far it is confirmed by observation. The treatment will be restricted to refraction as it affects marine navigation. This is a considerable simplification. Aerial observations may be made at any level between the ground and the lower stratosphere, so that air navigation involves a much greater range of pressures and temperatures at the position of the observer. Moreover, it involves some occurrence of much more strongly negative altitudes than can be observed from bridge height on a ship, and at such negative altitudes (i.e. zenith distances over 90°) the intrinsic variability of the refraction is large enough to make any table rather unreliable.

The accuracy of winds measured in flight using a doppler navigation system has been investigated by comparison with simultaneous measurements from a Meteorological Office radar wind-finding station and also by flying different tracks using a modified multiple-drift technique. The errors of wind measurement arise from errors in the ground-speed vector as measured by the doppler navigator and also from errors in the true airspeed vector as obtained from the readings of the airspeed indicator, altimeter, outside air thermometer and compass. The trials, which were made at various altitudes to 48,000 ft. in a Canberra aircraft of the Meteorological Research Flight, showed that, providing suitable in-flight calibrations are carried out, the error in the vector wind can be reduced to about 5 kt. but that without these calibrations it may be 10 kt. or more.

This paper was presented at the 44th Annual Meeting of the US Institute of Navigation in Annapolis, June 1988.

Navigational systems are usually thought of in terms of locating vehicles and craft over a range of hundreds or thousands of miles. There are, however, applications where navigation systems with a range of a few miles and an accuracy of inches can be very useful. Farming is one of these applications and this paper identifies the specific operational aspects that can benefit. Precise navigation could facilitate a lowering of input costs by an estimated jo per cent on a western dryland farm.

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.

As part of the overarching research goal to assess current and potential maritime information sources for use in maritime defence and security in the Canadian north, we examine whether wide-area surveillance data, as represented by Space-based Automatic Identification System (S-AIS) data, offers sufficient information for surveillance requirements in the Canadian north. If S-AIS data are not sufficient, we address how the additional information provided by Long-Range Identification and Tracking (LRIT) can be used to meet the surveillance requirements. A Systems Tool Kit (STK) simulation scenario is constructed that includes five exactEarth satellites collecting AIS data. Simulated AIS transmitters are positioned at 20 northern Canada ground locations. The results indicate that for each location, two thirds of the eight-day simulation is spent without a satellite within range, when using the five satellites. As the number of satellites decreases, intervals in the range of 80 to 105 minutes, during which there are no AIS messages received, increase in frequency. If the end-user requires vessel location information more often than S-AIS consistently provides, augmenting the S-AIS information with LRIT polling should achieve the desired vessel traffic awareness.

Accurate charts of tidal streams are needed in many fields of science and industry. The Proudman Oceanographic Laboratory's numerically modelled hydrodynamic data sets provide a suitable source for the production of such charts. Different methods of producing data in ‘tidal diamond’ format were investigated and the most suitable was selected for implementation over the UK continental shelf.

In the Interim Report of the Institute's Collision Regulations Working Party (Journal, 23, 448), it was stated in the preliminary that Dr. Calvert was not able to subscribe entirely to propositions (1)to (19). Dr. Calvert here states his views.

My disagreement with the interim report is concerned only with the propositions and principles at the end. The body of the report I regard as masterly in the circumstances.

Multipath arises from the reception of reflected or diffracted signals in addition to the Line-Of-Sight (LOS) signal. By using a block processing high sensitivity receiver scheme, this paper aims to obtain better positioning performance in urban canyon areas. Generally, the peak with the most power is utilised in high sensitivity receivers; however, this approach is not always optimal in multipath environments. Noting that signal correlation peaks may be separated in the Doppler domain by a long coherent integration time, a peak identification scheme is proposed in this work, which yields better positioning performance. It is shown that most of the multipath peaks are removed in the receiver after using the proposed algorithm.

The paper presents the error characteristics of a vehicle dynamic model (VDM)-based integration architecture for fixed-wing unmanned aerial vehicles. Global navigation satellite system (GNSS) and inertial measurement unit measurements are fused in an extended Kalman filter (EKF) which uses the VDM as the main process model. Control inputs from the autopilot system are used to drive the navigation solution. Using a predefined trajectory with segments of both high and low dynamics and a variable wind profile, Monte Carlo simulations reveal a degrading performance in varying periods of GNSS outage lasting 10 s, 20 s, 30 s, 60 s and 90 s, respectively. These are followed by periods of re-acquisition where the navigation solution recovers. With a GNSS outage lasting less than 60 s, the position error gradually grows to a maximum of 8⋅4 m while attitude errors in roll and pitch remain bounded, as opposed to an inertial navigation system (INS)/GNSS approach in which the navigation solution degrades rapidly. The model-based approach shows improved navigation performance even with parameter uncertainties over a conventional INS/GNSS integration approach.

In 1964 during the second single handed transatlantic race Colonel H. G. Hasler in Jester lost the correct time and, having no radio, could not get a time check. Thus he could not obtain the longitude but, being a fine seaman and practical navigator, made a landfall on Nantucket light-vessel by a method used by old sailing ship skippers. This was to position himself on the correct parallel of latitude and sail due east or west to the destination.

In this study, satellite based pseudo-range measurements are integrated with accelerometer measurements made by six accelerometers located on the six faces of a cuboid, to independently measure the translational and rotational accelerations, and the pseudo-range. These measurements are then processed by an adaptive Unscented Kalman filter (UKF) to correct for the estimated errors and to obtain the required position and velocities at two independent locations. The relative position and velocity are then obtained by the application of standard vector identities. From these estimates, the position and velocity kinematics of prosthetic limbs and measurements of the joint angles, the true ambulatory position is estimated using a third independent UKF based estimator. The robotic limb joint offsets are assumed to be biased which are also estimated by the third UKF. The basic assumption is that the errors in the measurements are quite similar at the two locations and for this reason it is hypothesised that these errors would be reduced when the relative position and velocity were estimated. The results indicate that the steady-state ambulatory position error of the end-effector is reduced by more than 98%.

The traditional Kalman filtering-based transfer alignment methods largely depend on prior information for initialisation. However, the initialisation process is hard to fulfil on a moving base. In this paper, a type of inertial measurement vector integration matching for optimisation-based transfer alignment and calibration is proposed to estimate the misalignment between the Master Inertial Navigation System (MINS) and Slave Inertial Navigation System (SINS), and main inertial sensor error parameters of SINS, including bias and scale factor error. In contrast to filter techniques, the proposed method has the capability of self-initialisation and provides a new idea to solve the alignment and calibration problem. No prior information is needed. Moreover, the integration time interval for the matching inertial measurement vector is selected by considering both the observation degree of inertial sensor error parameters and the noise effect. Simulation results demonstrate that the proposed method has faster convergence and is more accurate than Kalman filter techniques.

Vector-based maps are an advanced capability of digital moving-map systems that are easily customised and can be powerful aids to aircrew information processing and decision-making. However, they may place excessive demands on an aircrew's information processing requirements, cause an increase in workload, and degrade situational awareness if the user interface is not designed properly. There is little information available about the human factors and situational awareness issues relevant to vector-based maps. In this paper, we summarise relevant research on human factors and situational awareness aspects of using vector-based maps, identify key issues, and recommend directions for future research.

The correct ambiguity resolution between reference stations is the core issue of the whole Network Real-Time Kinematic (RTK) technology. Aimed at long fixed time and low reliability of the low elevation angle satellite ambiguity resolution during the initialisation of the Network RTK system, a three-step algorithm is proposed in this paper. Firstly, the double difference wide-lane ambiguities are fixed on the basis of the Melbourne-Wubbena (MW) method. Secondly, the double difference L1 carrier phase ambiguities of the high elevation angle satellites are fixed rapidly based on the ionosphere-free combination model. Thirdly, the corresponding ambiguities of the satellites with low elevation angles are solved with restrictions from the double difference tropospheric information, which is obtained from observations of the high elevation angle satellites. Based on this algorithm, an overall scheme of the ambiguity resolution during the initialisation process of the Network RTK system is designed. Results from Global Positioning System (GPS)/Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) data demonstrate that the three-step algorithm can reduce the ill-posed problems of the observation model effectively. Moreover, the speed and accuracy performances of the ambiguity resolution for the low elevation angle satellites using the proposed algorithm are better than those of the conventional method.

The aim of this paper is to provide a collective overview of current state-of-the-art weather routeing and it is therefore intended to give a descriptive appraisal. Essentially the paper will concentrate upon the vessel route optimization procedures, data-handling techniques including the parameters necessary to implement the methods, the ship-resistance characteristics and the James speed performance curves.

The year 1952 is the fourth centenary of the birth of Sir Walter Ralegh. So far from being the great romantic of tradition Sir Walter was a hard-headed practical man, and the first Englishman to engage a scientific and technical expert to advise him on his colonizing enterprises. He brought the brilliant young mathematician Thomas Hariot, some eight years his junior, direct from Oxford to Durham House, his mansion in the Strand, where, setting his instruments up on the leads, Hariot laboured for years at improving observational technique and revising the Ephemerides. Meanwhile he gave instruction in navigation to the officers of Ralegh's ships, himself obtaining practical experience on the voyage to Virginia in 1585, when he was able to observe the seaman's difficulties and the errors to which he was prone. He had already by 1584 written a new Instruction Manual which he entitled Arcticon, but this is unfortunately lost. We have, nevertheless, an epitome of its contents, for Ralegh asked for a ‘refresher course’ on the eve of his departure for Guiana, which was to take place in February 1595, and Hariot's teaching notes in his own (very crabbed) handwriting, besides fair copies of the tables he drew up, are now at the British Museum.

The UnScented QUaternion Estimator (USQUE) has been approved as a promising substitute for the extended Kalman filter when applied in the Standard Inertial Navigation Equations (SINE)-based inertial navigation system/global positioning system integration. However, the expensive computational burden makes it untenable in real time applications. In this paper, a computationally efficient filtering algorithm called Marginalised USQUE (MUSQUE) is derived by embedding the Marginalised Unscented Transformation (MUT) that is applicable to nonlinear systems with a linear substructure into the widely used USQUE. The contributions of the MUSQUE developed here are twofold. Firstly, the SINE are reconstructed to be only nonlinear in the attitude quaternion while linear in velocity and position, which makes the MUT potentially applicable in the USQUE. Secondly, the quaternion and generalised Rodrigues parameter-based sigma points are propagated simultaneously in the MUSQUE to deal with the dimensional mismatching hierarchy of the USQUE. Compared with the USQUE the number of sigma points can be decreased substantially, thereby making the applied MUSQUE computationally tenable. The experimental results show that the proposed MUSQUE has nearly identical performance with the USQUE but with much reduced computational burden.

On 14 September 1494, Christopher Columbus observed a lunar eclipse while at the island of Saona near the eastern tip of Hispaniola. He later recorded in his Libro de las Profecias that, from his timing of the eclipse, he determined his longitude to be ‘five hours and more than one half’west of Cape San Vicente. His actual longitude was three hours and 59 minutes west of Cape San Vicente, so Columbus was off by over an hour and a half, some 23 degrees of longitude.