LECTURE 16 
UNDERWATER ACOUSTICS AS A TOOL IN OCEANOGRAPHY 
M.J. Tucker and A.R. Stubbs 
National Institute of Oceanography 
Wormley, Surrey 
England 
16.1. INTRODUCTION 
Electromagnetic waves are severely attenuated in sea water, but fortunately 
sound travels well enough to be used for many of the purposes served by radio 
and radar in the atmosphere. Historically, the principle was first applied to 
find the depth of the sea; a sound impulse was made in the water and the time 
it took for the echo from the sea bed to return to the ship was measured. As 
techniques for this "echo-sounding" were developed, it became apparent that 
echoes were also being obtained from objects in midwater. These turned out to 
be fish shoals, and nowadays no fishing boat of any size would put to sea without 
an echo-sounder for locating fish. 
Probably the most important scientific application has been the examination 
of the geology of the sea bed. In suitable areas it has been possible to determine 
the geological structure of the sea floor in more detail than is possible in many 
land areas, and much useful information is being obtained about the transport 
of sediments. 
In the realm of biology, the habits of fish shoals have been determined using 
a scanning asdic to follow their movements, and something has been learned 
about the habits and composition of plankton. This is a fascinating field in which 
acoustics should be a powerful tool, but the application is still in its infancy. 
The telemetering of information using the acoustic wave as a carrier is also in 
its infancy, but is potentially of wide application. 
16.2. MARINE GEOLOGICAL APPLICATIONS 
16.2.1. Precision Echo-Sounding 
The method of measuring the depth of the sea by transmitting a pulse of 
sound from the ship and measuring the echo-time is well known. In the last few 
years, major improvements in the technique of echo-sounding in the deep sea 
have been made, notably at the Woods Hole Oceanographic Institution [1] and at 
the Lamont Geological Observatory, and it is now possible to measure depths 
of 3000 fathoms or more to an accuracy of one fathom in any weather in which 
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