This paper is the fifth chapter of a series on the history of air navigation systems. Comments on the content of the paper would be welcomed by the author and the editor.

This paper and the following five papers were presented at the DSNS-94 Conference organized by the Institute from 18–22 April in London. The full proceedings, including some 78 papers, are available from the Director, price £40 (exc. P&p).

This paper describes the infrastructure and concept of two multi-site reference station differential GPS (DGPS) options being offered to land and marine users by Racal Survey. The infrastructure of the Racal SkyFix system is briefly outlined followed by descriptions of Racal's internetting and network capabilities.

The two systems are compared including infrastructure, differential data management, user coverage, datalinks and positioning performance in various parts of the world. The paper describes the design of each of the systems and the tests undertaken to assess their functionality, before going on to compare their performances under a variety of conditions. Emphasis is placed on the technical issues associated with multi-reference station DGPS including error sources, weighting observations and monitoring of the data. The fundamental approach of the systems is shown to achieve high data integrity which is necessary to develop the systems to their next phase.

Having described the two options, examples of various combinations of reference stations are used to illustrate the potential of the system and to show the increased performance over ordinary, single-station DGPS. The conclusions summarize the paper's findings and make recommendations for the future development of the system. The object of the developments so far have been to improve the quality of real-time offshore DGPS positioning. The internetting and network options are providing real-time results to illustrate the benefits and, together with SkyFix, offer significant developments in the ability of DGPS to provide accurate and reliable positioning over vast areas of the world.

Use of multi antenna GPS equipment for determination of a vessel's attitude holds some promise for the development of accurate and inexpensive attitude systems. An application for such systems might be to provide very accurate roll information for multibeam echo sounders.

The present state-of-the-art GPS attitude systems cannot meet the required accuracy and update rate for such applications. GEOTEAM A/S has therefore developed a PC-based system which combines GPS-based attitude with roll and pitch information from a Vertical Reference Unit (VRU) and heading from a gyro compass.

In such a combined system, the long-term high accuracy of a GPS-based attitude system is combined with the short-term accuracy and fast update rate of conventional VRUS and gyro compasses in order to achieve a resulting performance that is better than any of the systems. In effect, the GPS attitude is used to calibrate the VRU and the gyro compass in real time.

During the past year extensive tests have been performed with a system using a Trimble VECTOR II GPS attitude system with a 1 metre baseline between the antennas, both on a van (with an inertial navigation system as reference) and on a vessel. During November and December 1993 further tests were made with an Ashtech 3DF attitude system with longer baselines (7·5 m). These tests were made on a vessel where the combined GPS/VRU attitude was fed into a multibeam echo sounder. These tests were performed in cooperation with Simrad Subsea A/S, the multibeam echo sounder EM 1000 manufacturer.

For half a century, the Egyptians have been concerned about the coverage of all their local waters in the Mediterranean and the Red Sea with visual and electronic aids to navigation. As a result, they constructed several lighthouses and landmarks as separate entities. Long years of political friction and military conflict in the Middle East resulted in damage to the majority of visual and primitive aids to navigation, particularly in the Gulf of Suez (GOS), the Gulf of Aqaba (GOA) and the Red Sea.

This paper presents a summary of the flight evaluation of the DGPS-INS hybrid navigation system conducted at the National Aerospace Laboratory (NAL). First, the configuration of the flight experiments, including ground facilities, the measurement system, etc. is described. Secondly, the design concept for a method of estimating navigation errors using a Kalman filter is presented. Thirdly, flight profiles employed in the experiments are defined, and the experimental results of GPS, DGPS, INS, in both stand-alone and hybrid modes are shown corresponding to each profile, and the improvement of navigation performance by the introduction of the DGPS-INS hybrid navigation system is experimentally verified. Fourthly, the future plan for research on the DGPS-INS hybrid navigation system at NAL is briefly explained. Finally, it is concluded that the design concept of the DGPS-INS hybrid navigation system available for future space vehicles has been successfully completed.

Even today much time is lost in bringing effective help when an accident with a truck carrying dangerous goods occurs. The location of the accident is often not well described by the people reporting it. Often it is difficult to determine what sort of freight a lorry is carrying, for example when the vehicle is burning, and sometimes the fire brigade does not bring the appropriate extinguishing equipment for the first help approach. Now an emergency location system is under development which will remove all these disadvantages. For immediate help on car accidents, an automatic alert message is transferred from the crashed vehicle via the emergency call centre to the fire brigade, the police station or the headquarters of an ambulance. The alert is initiated by a crash sensor within the car or the truck. The data channel between vehicle and base can be a radio link or, for longer distances, a mobile telephone connection using CNET or GSM. AS help is faster and more effective with this system, environmental damage caused by dangerous goods can be reduced.

In Stuttgart the mobile part of the DGPS-based emergency location system has been integrated in several vehicles. The full system is being tested within a field trial of a pilot project called STORM (Stuttgart Transport Operation by Regional Management), which is part of a programme of the European Community. The results of these tests are summarized in this paper. The integration of the system into fleet management applications is also considered.

The trend in the western military towards ‘superiority through technology’ has led towards the requirement for more mobile and efficient forces and equipments to address their defence needs in an increasingly unstable and unpredictable post-‘cold war’ world.

The national SAR (search and rescue) objective is to prevent loss of life and injury through search and rescue alerting, responding and aiding activities. Specific objectives under the SAR Branch's five year R & D (research and development) plan are: reduction of search time, improvement of rescue technology, and systems integration. The project described in this paper falls under the first objective – reduction of search time.

This paper derives a fast satellite selection algorithm; that is, an algorithm to select the best subset of satellites to use for positioning in circumstances whereby a satellite navigation receiver is not capable of using all satellites in view. The algorithm adopts the weighting factor concept to determine the contribution of each satellite to the overall positioning accuracy. Selection by this algorithm is shown to be especially efficient when the number of available satellites is large, so it is likely to be particularly useful for receivers capable of making combined measurements to GPS and GLONASS satellites.

This paper examines first a statistical modelling of the number of navigational accidents (collisons, groundings and strikings) involving tankers and freighters in Canadian waters; it then looks at a direct method of modelling oil spill frequency and magnitude, given a navigational accident. The former is used to examine various hypotheses in the literature regarding the impact of various factors on navigational risk. The latter is based on a direct probability tree analysis which allows the estimation of detailed oil spill impacts by facilitating the examination of representative spill sizes.

Sweden and some other countries are currently evaluating and verifying the potential impact of a newly developed, satellite-based GNSS transponder system on future CNS/ATM and ATN systems.

The concept provides the possibility to introduce a distributed, mobile, real-time data processing system, for all properly equipped users in the global civil aviation community being interacting members (air/air, air/ground and ground/ground).

Human error accounts for a number of collisions at sea; nevertheless, it is widely accepted that vessels are inclined to produce widely varying ranges of radar echo strengths in real sea conditions, in contrast to their ‘true’ anechoic strength, which tends to be minimal for a small and structurally non-reflective craft; even for the calmest possible water conditions.

In this paper experimental results for small craft will be presented and analysed in an exploration of potentially influential parameters in such cases. These results are based on three series of sea trials. Furthermore, an attempt is to be made to portray the inherent, theoretical and/or practical, limitations in the radar detection of small craft in real (estuary) sea conditions.