• Specific recommendations 



1. Continue to support technology and data processing in the following 

 general areas. 



a. Acoustic reflection profiling (e.g., air gun, sparker), especially 

 in the new techniques of multichannel, long-array technology. 



b. Measurements of sediment and rock layer interval velocities, with 

 expendable sonobuoys and multichannel, continuous reflection profiling using very long 

 arrays and special laboratory processing of tape-recorded signals (as presently done in oil- 

 industry geophysical exploration). Interval velocity measurements in the first tens of 

 meters (to about 100 meters) using high-resolution, higher-frequency equipment (3.5 

 kHz) has shown promise. 



c. Study of velocity gradients in sediment and rock layers. 



d. Measurements of acoustic impedance of reflectors as seen by 

 acoustic reflection profiling (some preliminary work has been done by Knott and his 

 colleagues at Woods Hole). 



2. Continue support of scientific expeditions that gather acoustic reflection 

 and interval velocity information at sea. This has been a long-term program of the Office 

 of Naval Research (ONR) and the National Science Foundation (NSF). 



Sediment and Rock Properties 



• Compressional wave (sound) velocity 



1. Support laboratory and, especially, in situ measurements of sound veloc- 

 ity and associated properties (and their relationships) in sediments and rocks (as in cores, 

 in boreholes, and with probes inserted into the sea floor). 



2. Support in situ measurements of sound velocity gradients in the upper, 

 surficial sediments (tens of meters), as with the special corer developed by Applied Re- 

 search Laboratories, University of Texas, or in boreholes. 



3. Although the Navy is not directly involved in the Deep Sea Drilling 

 Project, the Navy should encourage NSF to strongly support downhole logging of sound 

 velocity and density. These logs were recently started by the DSD? and should continue. 



• Sound attenuation 



1. Support laboratory and, especially, in situ measurements of compress- 

 ional wave (sound) attenuation at frequencies from a few Hz to several hundred kHz. 



2. Study relations between attenuation and frequency and between atten- 

 uation and common sediment properties in all of the common sediment types, especially 

 in sands at low frequencies (a few Hz to 1 kHz); such studies facilitate and allow pre- 

 dictions of attenuation. 



3. Sound attenuation measurements and studies should include, at lower 

 frequencies, the whole sediment and sedimentary rock sections, and the surface of the 

 underlying acoustic basement. This would result in profiles and gradients of sound 

 attenuation with depth in the sea floor. 



