There are several ways of building THE ACOUSTIC POSITION 

 KEEPER (fig. 17. 15). One is a unit that squeals intermit- 

 tently until the batteries run down. Another type answers when 

 queried by the anticipated signal. With a single one of these, 

 it is possible for a ship to maintain its position at sea to within 

 about 1 mile in 3 miles of water. K three of these are used 

 in an appropriate technique, the position can be kept accurately 

 to within several feet. What we need to improve this kind of 

 work are better sources, better transponders, and, above all, 

 longer-lived batteries. The nuclear batteries are, of course, 

 the most promising. Corner reflectors can possibly be used 

 for this purpose with great economy but have not been tried. 



The THERMAL, PROBE (fig. 17. 16) was used for measuring 

 the heat flow out of the bottom sediments. From the cores, 

 of course, we can measure the heat conductivity of the sedi- 

 ment. 



A LARGE-VOLUME WATER SAMPLER (fig. 17. 17) is 

 needed for some types of radioactivity dating techniques, 

 such as, those using carbon-14 and strontium-90. Other pro- 

 grams could utilize it also. 



This is usually done in conjunction with a coring operation 

 so that we take a core, measure thermal gradient, and take 

 a deep water sannple simultaneously. This sort of doubling 

 up or tripling up, if you will, is necessary in order to increase 

 the efficiency of operation of the research vessels which 

 are rather expensive. 



Another problem is the measurement of the SOUND 

 VELOCITIES IN SEDIMENTS right at the bottom of the ocean 

 fronn places where core samples have been taken. If we can 

 get longer cores, this will become more and more important. 

 There is good evidence that rather peculiar velocity variations 

 occur in the bottom, or near the bottom (fig. 17. 18), and 

 that these may have a much more fundamental concern to 

 underwater sound than anybody has given them credit for to 

 date. 



Additional geophysical measurements will obviously be 

 made. It is necessary to make deep ocean tide meters and 

 probably a bottom instrument like the seismograph will be 



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