velocity is about 156 5 m/sec. Sound speed in the surficial 

 sediment is about 2.2 percent less than in the water just 

 above the sea floor. 



RECOMMENDATIONS 



1 . When underwater sound experiments involve 

 bottom-bounce propagation, a realistic geoacoustic model 

 of the sea floor should be derived from surveys, measure- 

 ments, and studies made, or taken, at or about the time of 

 the acoustic experiments. Preferably, the insonified area 

 should be designated by the person in charge of the acoustic 

 experiments. In an expedition into far areas, the ocean- 

 ographers should be an integral part of the scientific 

 personnel aboard the ship, or ships, conducting the experi- 

 ments. Geoacoustic models of the sea floor should be 

 published in a continuing series to aid studies of under- 

 water sound propagation. 



2. Increasing use should be made of in situ 

 measurements made from research submersibles. Studies 

 need to be continued of methods which allow the prediction 

 of in situ values from laboratory or surface-ship 

 measurements . 



3. Detailed layering within the upper part of the 

 sediment body should be determined on the scale of tens of 

 feet. At the present time this can be done from surface 

 ships in waters a few hundred feet deep, but in the deep sea 

 present technology appears to indicate use of deep sub- 

 mersibles, or deeply-towed transducers, although other 

 methods are possible. 



4. Future research programs involving the mass 

 physical properties of sediments, if intended to support 



36 



