THE NAVY OCEAN SCIENCE PROGRAM 45 



sounders that have been used on many different ships and in 

 most oceanic areas. These devices have provided relatively 

 accurate data on bottom topography, bottom roughness, and 

 particularly on bottom slopes (see "Major Accomplishments"). 



The thicknesses and acoustic properties of ocean sediments 

 are being investigated in a great variety of ocean structures and 

 physiographic provinces by means of seismic-reflection methods. 

 These investigations have used explosive and, more recently, 

 electrical, and pneumatic soiu-ces; for the upper sediments, echo 

 sounders are being used in the 3 to 12 kilocycle per second range. 

 Thicknesses and acoustic properties of underlying crustal and 

 upper mantle rocks are measured with refraction seismic meth- 

 ods in a wide variety of ocean structures and physiographic 

 provinces. 



Measurements are made of the acoustic properties of the 

 oceans and underlying rocks. The velocity structure in the 

 oceans is correlated with different types of water masses and 

 with geographic regions. Flat abyssal plains with sediment fill 

 provide the best conditions for long-range underwater sound 

 propagation. Bottom roughness has the effect of reducing the 

 range of propagation. The effects of hills and mountains is to 

 produce shadow zones in long range propagation. 



Scattering and loss of acoustic energy by the ocean bottom, 

 ocean surface, biological material, etc., are a subject of scrutiny. 

 The ocean surface and ocean bottom not only reflect sound but 

 scatter it in all directions. This phenomenon causes a loss of 

 sound energy in the desired direction and causes sound energy 

 to be deflected uselessly. Considerable support for research and 

 measurement of these phenomena form an important part of 

 the acoustic program. Deep scattering layers which cause 

 both loss and scattering of sound have long been known. These 

 layers have been found to consist of several species of marine 

 animals. These animals move vertically, apparently in response 

 to the available amount of light, rising to shallow depths during 

 night time and descending during the day. The identity of 

 these animals is not fully established, and a program is under 

 way to identify and measure the populations of the layers* and 



