This paper and the following 5 papers were presented at the Institute's RIN-96 Conference, held at the University of Southampton, in September 1996. Copies of the complete Proceedings may be obtained from the Director. Price £6 members, £8.50 non-members.

This is a time of unprecedented change in radio-navigation systems and practices. The rapid development of satellite technology is challenging navigation authorities in every country to question the future of terrestrial navigation systems. The technical adequacy of the new techniques is being demonstrated in many applications but there remain serious questions concerning the reliability, integrity and political control of the current satellite systems and their long-term future.

The paper describes the operational principles of the present satellite Global Positioning System (GPS) and GLONASS. It compares them with terrestrial aids, identifying their advantages and drawbacks. Accuracy, availability and integrity are considered. The reasons for the development of differential operation are examined.

Finally, the paper looks at the future of satellite systems and addresses some of the difficult institutional issues concerning satellite navigation with which navigation authorities worldwide are having to grapple. It reviews the development of the future Global Navigation Satellite System (GNSS) and identifies the economic benefits it could bring.

This paper was presented at a Workshop organized by the Institute in London in October 1995 on the subject of GPS Interference – Is it a Problem? Copies of the Workshop Notes can be obtained from the Director (£50 to Members, £75 Non-members, £10 to students).

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.