future developments in this field, of interest to underwater 

 acoustics, will probably involve better sound sources, 

 used from research submersibles running close to the sea 

 floor, and deep-towed transducer packages. Information 

 so derived, when combined with drilling into the sea floor, 

 will yield realistic, detailed information on layers within 

 the sea floor. 



Sediment and Rock Samples 



Two types of samples can be used in the production 

 of acoustic models. For measurements of sound speed 

 and attenuation, density, and some other properties, a 

 "least disturbed" type of sample is needed. These are best 

 obtained by special corers and snapper-type samplers from 

 ship or submersible, or by diving in shallow water. Enough 

 in situ measurements should be made to validate the 

 laboratory measurements and their relationships to in situ 

 values. 5 Coring can produce samples from the sediment 

 surface to depths of a few meters, but for deeper values it 

 is now necessary to extrapolate or use samples from holes 

 drilled into the bottom (such as the Mohole). 



A second type of sample is usable to determine lateral 

 distributions. This can be a seriously disturbed sample on 

 which no more than identification tests need be made (e_. g. , 

 analysis of grain size and constituents, and density). In 

 any given area, disturbed samples can be used in theoretical 

 and experimental studies to help determine limits of 

 physical properties. For example, the sand from the 

 shallow Bering Sea was used to determine the outside 

 limits of porosity with this particular sediment. 



Mass Physical Properties of Sediments and Rocks 



A great deal of theoretical and experimental work has 

 been done on sediments and rocks to determine such prop- 

 erties as sound speed, density, porosity, grain size, and 

 mineral constituents. Much of this information is found in 



