Engineering Applications of Underwater Acoustics in the Ocean

Abstract

Underwater sound has provided means for measuring distances for nearly half a century. The first successful means echo sounding is still the one most widely used. It is likely that continued research can make it a valuable oil industry tool in offshore exploration and operations. Introduction As the mineral industries exploit deeper and deeper areas of the ocean, they will almost certainly rely more and more heavily on underwater acoustical instruments. One can only guess at the instruments that will prove useful, but it may be helpful to describe some past experiences in naval research and development and indicate the paths of research and development that seem to be needed for producing a suitable array of acoustical tools for industry. Military Use of Underwater Acoustics Underwater acoustics has been employed in undersea warfare since World War I. It is used for detecting, tracking and localizing enemy targets, either submarines or surface ships; and some weapons are fired by means of acoustic sensors. The use of sound rather than optical or radar devices is dictated by the rapid attenuation of electromagnetic waves in sea water compared with that of air. The variability of the ocean both in place and time puts constraints on sonar systems that the navies of the world must know about in some detail that least where they expect to operate. As a result, an elaborate program of environmental research, focused on the needs of sonar, has paralleled and paced the development of military systems. Military sonar systems themselves. are not generally useful to industry because of their specialized design. Although some elements of these systems may be of interest because their development has advanced the state of the art, the most generally useful part of naval research and development probably will be the methods that have been developed for measuring the environment. In fact, in the continuing interaction with the oil industry particularly, several of the navy's methods and apparatus have already been adopted. Deep Water Exploration and Drilling The offshore oil development in the Gulf of Mexico, off Southern California, and in the Persian Gulf long ago heralded the exploitation of the mineral wealth of the ocean. Most of the resulting production has been in less than 100 ft of water. In the past 5 years, however, there has developed a powerful thrust into deeper water that has already carried the oil industry to the edge of the continental shelf and beyond, both in geophysical exploration and in drilling. Even very conservative prognostications indicate that oil wig be produced in several thousand feet of water in 10 to produced in several thousand feet of water in 10 to 20 years. The corresponding development of solid minerals from the sea floor is now estimated to be far slower. Nevertheless, the geology of the sea floor is imperfectly understood, to say the least, and there may well be some surprises awaiting us in hard minerals. Whether for oilfield development, which is upon us, or mining, which will develop more slowly, it is clear that much of the work must be done underwater. JPT P. 1277