angle reflection techniques. Compress ional sound velocities, however, 

 do not give unambiguous solutions to sediment tvpes . Since the shear 

 strength of the sediments is related to the shear wave velocities, its 

 measurement would be of immense value to the seafloor engineer. If the 

 compressional and shear wave velocities are known, the dynamic elastic 

 properties of the material, such as Poisson's ratio, can be calculated. 

 Shear waves, though transmitted by saturated marine sediments, are not 

 propagated through the water column and so are unavailable to surface, 

 or even deep-towed acoustic surveys. 



When both the compressional wave velocity and the reflectivity 

 coefficient of a stratum are known, the bulk density can be calculated. 

 The precise measurement of reflection energies, termed the reflection 

 coefficient, have been attempted with some success, but sediment types 

 cannot consistently be categorized, even broadly as clay, silt, or sand, 

 largely because of the rather widespread phenomenon of surficial sediment- 

 entrapped gas which produces a too-high reflection coefficient for the 

 host sediment. 



Three approaches to the problem are indicated: (1) the development 

 of shear wave determination techniques for a rapid measurement of sedi- 

 ment shear strength, (2) a more comprehensive and quantitative analysis 

 of the information of engineering value contained in the bottom-reflected 

 pulse, and (3) the development of a deep-towed, high-resolution subbottom 

 profiler. 



Shear wave measurements cannot be made underwav, disqualifying this 

 approach for site reconnaissance purposes. 



The second approach is being pursued, notably at the Naval Undersea 

 Research and Development Center, San Diego, California, and jointly by 

 Raytheon Company-University of New Hampshire. 



The third approach has not been vigorously pursued due primarily to 

 the limited number of potential users. The rquirement to conduct sub- 

 bottom profiling over small construction sites in water depths to 6,000 

 feet is not widespread and so has been bypassed by industry. 



It is proposed that a self-powered, deep-towed subbottom profiler 

 be designed and fabricated which will produce high resolution records 

 of at least the first 100 feet of soil in water depths to 6,000 feet. 



