An OCEAN BOTTOM SEISMOGRAPH, one of our latest in- 

 struments, is a throw away unit (fig. 17. 13). It is quite a largesse 

 to throw away this much equipment. On the bottom there is a de- 

 tector, some amplifiers, etc. Then the signal is put on the trans- 

 ducer and telemetered to the surface by frequency modulation on 

 a 12 kc. carrier. This is analyzed at the surface and recorded on 

 magnetic tape and also on a pen recorder so we can see what we 

 are getting immediately. These instruments also bring in rather 

 startling results. We have shot refraction profiles out about 

 three times as far as we can for surface refraction measurements. 

 We have seen some things in earthquakes that we have never seen 

 on land. We have not had very many of these working very long, 

 so we expect many other surprises when we get to use them more 

 extensively. 



It is necessary that these be extended to other frequency 

 ranges, and it is necessary that sonne form of recovery technique 

 be devised so that these instruments do not have to be thrown away. 

 As instrumentation gets more complex, it will become harder and 

 harder to tear yourself away from it. 



In addition to the gravity measurements (mentioned on p. 184), 

 many others can be made from a stable platform. Three-compo- 

 nent accelerometer s are kept in position relative to the vertical 

 reference. A great deal is being learned about ship motions from 

 such records. I suspect that we might do quite a lot better for 

 ship's navigation if we just tied the master's sextant to our stable 

 platform and brought it up on deck and let them look at the stars 

 without having to see the horizon; but we at Lamont have not tried 

 this yet. This would be, of course, a stop-gap type of measure. 



Figure 17. 14 shows the ray diagrams for a sofar shot. This 

 is an explosion made 700 fathoms deep in the Atlantic, and about 

 400 in the Pacific. The ocean acts like a speaking tube. The sound 

 is relegated to within the body of water in the ocean, and we have 

 heard sounds from a 50-pound explosion as far as 14, 000 miles 

 away, half way around the world by this method. It is useful in 

 many ways. It can be used as a navigational scheme. To date, 

 its accuracy has not been adequately tested. It is possible to 

 use it to locate life rafts at sea. It is a quick method of survey- 

 ing for higher parts of the topography and has been so used, etc. 



190 



