If you ask the average Briton, he will tell you that Robert Watson-Watt invented radar in 1935. A German, asked the same question, would reply Christian Hulsmeyer in 1904. Strictly speaking, neither reply would be correct. It is generally accepted that the acronym RADAR stands for “Radio Direction and Ranging”, thus a practical radar system requires that both direction and range be determined. For this, the development of high power pulse transmission, and techniques for direction finding and timing of very short time intervals were needed. Over a period of years, these were individually developed for other purposes, but radar arrived only when all were combined into a single system. By 1939 radar development was also proceeding in a number of countries including France, Holland, Russia and the USA, but only the United Kingdom and Germany had brought it to an operational state.

The maritime radiobeacon differential GNSS service in Europe has recently been reorganised with the aim of having at least two of the 162 stations serve each critical coastal location. Maritime administrations have now set specifications for the availability and continuity of the service. The paper analyses these requirements, noting incompatibilities between them. It proposes a method of predicting the performance of beacons, employing IALA standards. This takes into account each beacon's own availability, and propagation factors that include groundwave signal attenuation, interference, and skywave fading at night. Availability, continuity and coverage maps produced by the new programs are presented in the paper.

Collision avoidance is an intensive discussion issue for navigation safety. This article introduces a new routing algorithm for finding optimal routes with collision detection and avoidance on raster charts or planes. After the required data structure of the raster chart is initialized, the maze routing algorithm is applied to obtain the particular route of each ship. Those ships that have potential to collide will be detected by simulating the particular routes with ship domains. The collision avoidance scheme can be achieved by using the collision-area-marking method with collision avoidance rules at sea. The algorithm has linear time and space complexities, and is sufficiently fast to perform real-time routing on the raster charts.

Onboard train positioning (navigation) plays a vital and safety critical role in advanced Automatic Train Control (ATC) and Automatic Train Protection (ATP) systems. Such onboard systems are also essential for moving block signalling and control systems for railways. The application of multi-sensor fusion algorithms to the vehicle navigation field has made it possible to create inexpensive and accurate positioning systems, which will satisfy the railways' requirements. The state estimation methods involved in Kalman filtering have proved to be some of the most effective techniques in multi-sensor data fusion. A multi-sensor navigation system is introduced in this paper to address the shortcomings of the existing train positioning systems. The proposed system utilizes the Global Positioning System (GPS), Doppler radar, gyroscopes, tachometers, digital maps and balises. In order to provide fault detection and isolation capabilities, a hierarchical structure is proposed for the multi-sensor integration system in which different combinations of navigation systems would function. Several data integration nodes, including DR/GPS, DR/Balise, and DR/GPS/Balise, are studied in more detail and their performances are evaluated.

A model is developed for lateral collision risk in air traffic track systems, which resolves the problems of the Reich Model. It is a direct and concrete approach focusing on events, in contrast to Reich's synthetic methodology, in which (e.g.) three types of collision have to be modelled and the focus is on flying hours spent away from the planned flight path. This model makes it straightforward to see what is being assumed, and easy to understand the roles of the main parameters. It is a good starting point for the incorporation of collision detection and the use of hazard analysis.

This paper is based on two articles by the authors that were published in the March and September 2002 issues of the Journal of Japan Institute of Navigation.

The collision risk to multiple targets and identification of feasible evasive manoeuvres can be assessed simultaneously in true motion by judging the tip of own ship's velocity vector in relation to the display of cone-shaped collision danger regions to acquired targets. Simulator test programmes composed of scenarios with various traffic densities and different speed ranges of own ship have been carried out in order to evaluate the performance of this collision avoidance display versus ARPA (true and relative motion) displays. Experienced navigators and maritime university students with license participated as test subjects. It is shown that the proposed display is capable to facilitate more homogeneous, precise and safe evasive manoeuvres than utilising conventional judgement techniques. The superiority increases with the excess speed of own ship, traffic density and complexity.

A localization system using GPS, ABS sensors and a driving wheel encoder is described and tested through real experiments. A new odometric technique using the four ABS sensors is presented. Due to the redundancy of measurements, the precision is better than the method using differential odometry on the rear wheels only. The sampling is performed when necessary and when a GPS measurement is performed. This implies a noticeable reduction of the GPS latency, simplifying the data-fusion process and improving the quality of its results.

The Global Positioning System (GPS) is now attracting worldwide attention as a navigation sensor. One of the advantages of GPS is that people can find their position using a GPS receiver wherever they are except in obstructed environments. Existing GPS receivers do not work in an obstructed environment despite there being many potential applications. This paper shows the possibility of navigation using GPS technologies indoors in a blocked environment. The paper describes the pseudolite-based indoor navigation system that was developed and implemented at Seoul National University (SNU). The system, which uses GPS technologies, has some different characteristics to normal outdoor GPS systems. The differences cause some practical problems, such as near/far, time-tag, multipath and unknown transmission position problems, which need to be solved to implement the indoor navigation system. The paper introduces various methods for solving such problems. The paper then shows the experimental results and the system accuracy. The satisfactory experimental results show that the RMS static error is 1 mm(1σ) horizontally and 2 mm(1σ) vertically and the RMS dynamic error is 5·6 mm(1σ) horizontally and 15 mm(1σ) vertically. The paper also shows the result of a field application test in the ocean engineering basin of the Korea Research Institute of Ships & Ocean Engineering (KRISO).

A geometric approach to Low Earth Orbiter (LEO) precision orbit determination (POD) based exclusively on triple-differenced GPS carrier phase observables is presented. The algorithm is fast and efficient because there is no ambiguity-resolution requirement, which is a complicated and time-consuming task for long-range kinematic GPS. However, the triple-difference kinematic LEO POD requires careful screening for cycle slips, as the orbit quality depends on the accuracy and the geometry of the observations. It is shown that the signal-to-noise-ratio (SNR) combined with residual screening offers a good approach to data cleaning. Data from a CHAMP (Challenging Minisatellite Payload, altitude ~450 km) mission are used to present the accuracy, speed and efficiency of the processing algorithms. The methods of data screening and the effects of geometry on the orbit quality are discussed and the final achievable accuracy including the limitations and benefits of this method are quantified. It is demonstrated that the triple-difference method offers short processing times and is currently capable of achieving a 3D RMS fit to the dynamic orbit of 15–30 cm and 1 mm/s to the velocity.

To ensure high accuracy results from an integrated GPS/INS system, the carrier phase observables have to be used to update the filter's states. As a prerequisite the integer ambiguities must be resolved before using carrier phase measurements. However, a cycle slip that remains undetected (and uncorrected) will significantly degrade the filter's performance. In this paper, an algorithm that can effectively detect and identify any type of cycle slip is presented. The algorithm uses additional information provided by the INS, and applies a statistical technique known as the cumulative-sum (CUSUM) test. In this approach, cycle slip decision values can be computed from the INS-predicted position (due to the fact that its short-term accuracy is very high), and the CUSUM test used to detect cycle slips (as it is very sensitive to abrupt changes of mean values). Test results are presented to demonstrate the effectiveness of the proposed algorithm.

This paper shows a possible new use of a common or computerised star finder for a rapid and easy solution to some space problems such as:

1. – launch windows;

2. – satellite fly-over;

3. – the rise and setting of a satellite;

4. – Earth or Moon satellite surveys;

5. – the eclipse of a satellite.