cm. 30,5 x 22, pp. 196, copertina rigida con sovraccoperta, in ottime condizioni.
Drilling for oil at sea, particularly in the North Sea, has made exacting demands on the accuracy of location of oil rigs out of sight of land. Fortunately, an excellent system for quickly determining position at sea was already available, the satel lite Doppler method of the U.S. Navy Navigation Satellite System (N.N.S.S.), also known as the Transit system. Five artificial satellites, moving in near-circular polar orbits at heights of about 1100 km, broadcast radio signals on accurately maintained frequencies and, by measuring the Doppler shift of the received frequency, the position of the receiver can be determined. The accuracy attainable by the system has been dramatically improved in the past 15 years, and position may now be determined by using fairly inexpensive battery-operated receivers, with an accuracy or relative accuracy of 1 m, depending on what satellite ephemeris information is available. The N.N.S.S. also provides results of great scientific interest, because the measure ments from the permanent tracking stations can continuously determine the time-varying co ordinates of the Earth’s pole with an accuracy as good as that of the classical astrometric techniques.
This volume contains invited papers presented at a two-day Discussion Meeting held at the Royal Society on 10 and 11 October 1978, together with a record of the discussion. The purpose of the meeting was to bring together practical users and scientists, and to discuss methods by which improved accuracy is sought and achieved, with reference to the practical problems of the positions of oil wells in the North Sea, and the scientific advances made possible by the Doppler methods. The final paper looks to the future, with a description of the Global Positioning System, which is due to become operational in 1985.