The following is the second part of an extract from the memoirs of Dr. J. A. Pierce who was deeply involved in the development of radionavigation aids in the USA between 1941 and 1973. These are, of course, personal reminiscences, and some issues might be challenged by others working in the same field at the time. However, they give a remarkable insight into the problems faced by the scientists of the day and how they were overcome. The editing principle used here has been to rigorously preserve Dr. Pierce's own wording while eliminating those parts of a purely personal nature. The entire original document without cuts may be found on www.internationalnavigation.org.

The associate members of the North European LORAN-C System (NELS) will, before the end of the six-nation co-operation agreement in 2004, need to take a decision whether to prolong or decommission LORAN-C operation in Europe. The Minister of Fisheries in Norway has already indicated decommissioning of the Norwegian LORAN-C stations. Such a decision raises the fundamental debate about whether we can rely on GPS as a ‘sole-means’ system, or if we need a secondary backup system, such as LORAN-C. The purpose of this article is to highlight important aspects and conflicts related to an extension of LORAN-C in Europe. The focus will therefore be towards the limitations and vulnerability of GPS vs. the potential of LORAN-C improvements. The discussion will be based on a Norwegian nautical perspective.

This is the first of two papers on Quantitative Safety Assessment – vital to the successful introduction of future Air Traffic Management systems. The goal of the two papers is to identify key future questions and the best methods to deal with them. The focus is en route European commercial traffic in controlled airspace, particularly risks from mid-air collision. Part 1 is a critical sketch of the historical context, methods used, and the use of analytical ‘models’ for safety assessment. Aspects covered include safety philosophy principles, safety targets, procedural separation standards, the Reich model and its problems, and radar separation standards.

This paper discusses issues relating to the practical application of the collision avoidance regulations (COLREGS) from the sociological viewpoint that rules are always contingent, defeasible and that no rule can exhaustively specify the conditions of its use. It is proposed that, due to the inherent nature of rules, the only way successfully to manage collision risks at sea, is physically to separate opposing traffic flows, so as to remove the interpretative and mutually co-ordinating factors from the COLREGS.

The increasing availability of small, low-cost GPS receivers has established a firm growth in the production of Location-Based Services (LBS). LBS, such as in-car navigation systems, are not necessarily reliant on high accuracy but a continuous positioning service. When available, the accuracy provided by the standard positioning service (SPS) of 30 metres, 95% of the time is often acceptable. The reality is, however, that GPS does not work in all situations, and it is therefore common to integrate GPS with additional sensors. The use of low-cost inertial sensors alone during GPS signal outage is severely restricted due to the accumulation of errors that is inherent with such dead reckoning (DR) systems. Through the integration of spatial information with real-time positioning sensors, intelligence can be added to the land mobile navigation solution. The information contained within a Geographical Information System (GIS) provides additional observations that can be used to improve the navigation result. With this approach, the solution is not dependent on the performance capabilities of the navigation sensors alone. This enables the use of lower accuracy navigation devices, allowing low-cost systems to provide a sustained, viable navigation solution despite long-term GPS outages. Practical results are presented comparing solutions obtained from a hand-held GPS receiver to a gyroscope and odometer.

This paper, and that following, were first presented at NAV 2001 – Location and Navigation – held at Church House, Westminster, London, 6th to 8th November 2001. Full Proceedings of the Conference are available on CD-ROM from the Royal Institute of Navigation.

This paper covers the current status of wireless network location capabilities, including a view of each method describing the strengths and weaknesses of the various approaches. The paper will describe developments in network-assisted GPS to reveal the capabilities of the so-called high sensitivity receivers. The question of what has to be done to get GPS to work indoors will be answered, together with the impact of this capability on the positioning of mobile telephones fitted with GPS capability. The paper discusses the concepts of integrating terrestrial network-derived location with GPS/GNSS and very short range location systems such as Bluetooth. It will explain how Location-Based Services are operated, when they will become widely available, some of the key applications and the impact of this technology on some of the traditional sciences, in particular mapping. This area of navigation is developing extremely rapidly, with potentially a huge market for navigation on land.

Marine radiobeacons are widely used by the maritime community worldwide as an efficient means of broadcasting differential GPS data to users at sea. In Europe and North America, large numbers of these beacons now serve coastal regions, waterways, and some inland areas. Frequently there is overlapping coverage and a choice of stations. But users receive little guidance as to how to select the beacon that gives the highest quality service. Receivers that choose a beacon automatically generally select either the nearest station or the strongest signal. But the performance of the data-link is optimised by choosing the station received with the highest ratio of signal to either noise or interference. With Selective Availability set to zero, spatial dilution and time-to-alarm have become key factors. This paper compares four beacon selection strategies by means of a computer model based on well-established coverage analysis and system design techniques. We recommend a new ‘post-SA’ beacon selection method that chooses the nearest station that meets the time-to-alarm requirement. This strategy has been used to identify the ‘best beacon’ throughout the European Maritime Area, with stations operating in accordance with the new band-plan adopted last September. We also identify the alternate beacon to use if the preferred station should fail.

The motivation for this paper was to provide computer support on the rules for sailing races. A brief overview is given of sailing terminology and racing rules. It is argued that a useful program for the racing rules should run on hand-held devices. The program should support an archive of rule scenarios, race training, self-learning of the rules, and analysis of rule disputes. SailRule is a freely available program intended to analyse and improve performance in applying the racing rules. The SailRule program has been implemented using the SuperWaba programming environment for hand-held devices. The user interface is described for the rules program. An explanation is given of the principles behind formalising and codifying the racing rules so that they can be efficiently implemented. Examples are given of how the program represents and analyses rule scenarios.

When anchorages are arranged in a harbour, the manoeuvering difficulty of a ship navigating between anchored ships should be considered. However, until now, nobody has researched how to design the arrangement of anchorages from the viewpoint of manoeuvering difficulty. In this paper, the relationship between the arrangement of anchorages and manoeuvering difficulty is systematically analysed by applying the Environmental Stress Model to the problems of a ship navigating between anchored ships. Based on this analysis, a method of designing the arrangement of anchorages is considered that ensures manoeuvering difficulty is at an acceptable level for mariners. The distance needed between the anchored ships has been proposed to accord with the length of the navigating ship and the mean length of anchored ships.

This paper describes an ionospheric correction technique for single frequency GPS measurements from satellites in low Earth orbit. The fractional total electron content (TEC) above the receiver altitude is obtained from global TEC maps of the International GPS Service network and an altitude dependent scale factor. By choosing a suitable effective height of the residual ionosphere, the resulting path delay for positive elevations is then computed from a thin layer approximation. The scale factor can be predicted from the assumption of a Chapman profile for the altitude variation of the electron density or adjusted as a free parameter in the processing of an extended set of single frequency measurements. The suitability of the proposed model is assessed by comparison with flight data from the Champ satellite that orbits the Earth at an altitude of 450 km. For the given test case, a 90% correction of the ionospheric error is achieved in a reduced dynamic orbit determination based on single frequency C/A-code measurements.

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).

This article is the second in a series dealing with the hand-held instruments and techniques navigators have used to find distance.

Warships frequently steam in tight formation in order to concentrate defensive gunfire. It is the Conning Officer's responsibility to keep his ship on station at an assigned range and bearing from the guide ship, usually the flagship of the Senior Officer Present Afloat. This can be an easy task when the fleet is steaming along peacefully, but it becomes a particularly challenging responsibility when the formation is changing course frequently under battle conditions. In such difficult situations, the Conning Officer needs all the help he can get.

In the days before radar, and even now when radar and laser are blacked-out, the Conning Officer had to rely on optical instruments to determine range and bearing. Bearing always has been easy – a pelorus mounted on the wings of the bridge gives bearing quickly and accurately. Measuring range is more difficult. Many ingenious instruments relying on prisms or the doubly reflecting principles of the sextant have been produced to simplify the task of finding distance (Ifland, 2002).