The Global Positioning System (GPS) offers an absolute positioning accuracy of 15 to 100 metres. Inertial navigation complements GPS in that it provides relative positioning and is totally self-contained. These two positioning sensors are ideally suited for system integration for although there is not necessarily an improvement in accuracy, the integration of GPS with inertial navigation systems (INS) does enable an increase in system performance.

The safety on board medium-sized fishing vessels in relation to working conditions on the bridge is analysed by means of a problem-solving method developed by the Safety Science Group of the Delft University of Technology. The potential of the method is illustrated by a number of case studies on selected aspects of the bridge design, since a complete application of the method is not yet available.

This paper is the second chapter of a series on Air Navigation Systems during the fifty years from the early oceanic flights and the inception of commercial aviation to the introduction of INS in civil aircraft. These papers are intended as critical commentaries. A definitive history has yet to be written. The writer would be grateful to receive criticisms of the paper or comments on the subject.

A new threat detection criterion is described which provides a better match to the requirements than the well-known modified tau criterion for a civil air transport collision avoidance system. Experimental evidence is given to show that it also reduces the number of undesirable alerts.

This paper was presented at the 14th annual meeting of the International Omega Association, held at Long Beach, California in October 1989.

The integration of Omega and GPS sensors into a single navigation system offers the advantages of good accuracy under almost all signal conditions, low capital investment, and certifiable worldwide navigation. The accuracy of the existing Omega network can be progressively improved as GPS satellite coverage is fully implemented. This is done by having the GPS system update the Omega navigator. Eventually, the same equipment can provide full GPS navigation accuracy but with Omega as a back-up.

This paper proposes a method of further improving the overall accuracy and reliability of Omega-GPS navigation. The conceptsof Omega-GPS integration, interoperability, modes of operation, and Kalman filter data fusion are presented. Four interoperability modes of operation and their ability to improve navigation reliability are also discussed.

The views expressed in this paper are those of the author and do not necessarily represent CAA policy.

The author would like to give grateful acknowledgement to the various companies from which information has been received. (Note that the original presentation at a RIN ordinary meeting was illustrated by numerous colour slides which cannot be reproduced here, as well as three video films).

Navigation aids in use today have their origin in mainly military operational requirements for navigation accuracy, coverage and integrity. They have also been directed at the needs of air and sea operations.

Multicollinearity and its effect on parameter estimators such as the Kalman filter is analysed using the navigation application as a special example. All position-fix navigation systems suffer loss of accuracy when their navigation landmarks are nearly collinear. Nearly collinear measurement geometry is termed the geometric dilution of position (GDOP). Its presence causes the errors of the position estimates to be highly inflated. In 1970 Hoerl and Kennard developed ridge regression to combat near collinearity when it arises in the predictor matrix of a linear regression model. Since GDOP is mathematically equivalent to a nearly collinear predictor matrix, Kelly suggested using ridge regression techniques in navigation signal processors to reduce the effects of GDOP. The original programme intended to use ridge regression not only to reduce variance inflation but also to reduce bias inflation. Reducing bias inflation is an extension of Hoerl's ridge concept by Kelly. Preliminary results show that ridge regression will reduce the effects of variance inflation caused by GDOP. However, recent results (Kelly) conclude it will not reduce bias inflation as it arises in the navigation problem, GDOP is not a mismatched estimator/model problem. Even with an estimator matched to the model, GDOP may inflate the MSE of the ordinary Kalman filter while the ridge recursive filter chooses a suitable biased estimator that will reduce the MSE. The main goal is obtaining a smaller MSE for the estimator, rather than minimizing the residual sum of squares. This is a different operation than tuning the Kalman filter's dynamic process noise covariance Q, in order to compensate for unmodelled errors. Although ridge regression has not yielded a satisfactory solution to the general GDOP problem, it has provided insight into exactly what causes multicollinearity in navigation signal processors such as the Kalman filter and under what conditions an estimator's performance can be improved.

The purpose of this paper is to show the effect of incorporating various discrete grid systems in a micro-based, ship weather-routeing system, which employs Bellman's dynamic programming algorithm, and either a cost-objective or time-objective performance measure. A simple ship speed and power function is utilized, in the cost computation. The calculation of the least-cost/least-time route is briefly described, but it is the derivation of the discrete grids and their influence on the route decisions that forms the paper's emphasis. The measure of cost within this paper is necessarily notional.

Meeting encounters, in which it is uncertain at what range the give-way ship will manoeuvre, are analysed using a model based on probability theory. Course alteration ranges of both giveway and (if necessary) stand-on ships are closely fitted by a simple mathematical model, which is also used to interpret the efficiency of the Collision Regulations.

This contribution is an updated version of a paper presented at the thirteenth annual meeting of the International Omega Association. It discusses the extraction of directional as well as positional information from the Omega signal pattern. The two outputs might be combined to form a self-contained, Omega-based, ship or aircraft navigation system, or the directional information could be fed to a conventional gyro-magnetic compass as an alternative to the magnetic input. Directional information from other VLF transmissions could also be used.

In the past, it was perfectly satisfactory for navigators to operate with little regard for the exact meaning of the terms, such as latitude and longitude, or even height, that they used to describe where they were. Latitude was latitude and longitude was longitude and that was the end of the matter. Of course, the positioning methods employed and the objectives of the positioning activity itself were usually so approximate that exact definitions were not important anyway, and no difficulties arose.

This paper presents a concept for selecting a fixed time ocean route via a prefixed grid of points. The ship is to sail with a fixed pitch propeller rotating at a constant rate N. The starting and arrival points A and B are given, as well as the starting and arrival times t0 and t1. The criterion is to obtain a route with a minimal value of N. The method is designed for a discrete navigating system. Thus it can be seen as an application of Bellman's Dynamic Programming Theory1. The ship's speed is estimated with the use of a modern algorithm, based on a well founded and well tested hydrodynamic model.

The collision between the dredger Bowbelle and the pleasure cruiser Marchioness on the Thames in August 1989 in the vicinity of the centre of London has drawn attention to the need for river mariners to keep a frequent look-out astern as well as ahead. This paper describes calculations of the minimum frequency at which observations astern are required in order to allow sufficient time for a ship about to be overtaken by a faster vessel to be able to take adequate avoidance action should the overtaking craft fail to keep clear.

In this paper the authors obtain analytical expressions for the ground traces of synchronous polar satellites on the polar orthographic projection, confirming that they are circles and pointing out a simple graphic method for the mapping of the subsatellite point.