314 Lecture 16 
APPROX 40 MINUTES. - Pe 
Fig. 16.14. Record from asdic equipment used as an echo-sounder showing migrating scattering layers. 
16.4, ACOUSTIC TELEMETERING 
16.4.1. General 
Compared with radio telemetering in the atmosphere, acoustic telemetering 
in the sea is in its earliest infancy. Marine scientists and engineers are con- 
stantly agitating for all kinds of telemetering devices: depth-of-net meters, 
devices for telemetering the behavior of dredges, telemetering temperature 
meters, and so on, but the number of people available in civilian establishments 
with the rather specialized knowledge necessary for the development of these 
devices is so small that progress is slow. 
It is perhaps relevant to ask way the information is not brought up via electric 
cables. Oil-well engineers, for example, lower equipment to similar depths in 
oil wells on strain-bearing cables incorporating one or more conductors, as a 
matter of routine. Oceanographers do in fact use similar cables, but they are 
not really satisfactory for several reasons. In many ways marine use is more 
severe than use in oil wells; in particular, because of the vertical motion of the 
point of suspension due to wave-induced pitching and rolling of the ship, and 
because of the extra strain, vibration, and twisting due to towing the cable through 
the water: even the normal drift of the ship or differential currents may be sig- 
nificant in this respect. 
Perhaps the difficulties can best be illustrated by considering a particular 
cable designed specifically for marine use by a specialist in the field. Briefly, 
