Acoustic Retrieval of Seafloor Geotechnics

Acoustic profiling is a rapid and relatively economical means of obtaining considerable information about large areas of the seafloor. Acoustic data can be quantified, and basic theory suggests that these data incorporate seafloor physical parameters similar to those used by geotechnical engineers in foudation and anchor design. This report summarizes the basic acoustic reflection theories and reviews earlier filed efforts to quantitatively classify the seafloor with acoustics. It appears that sediment density can be measured with an accuracy range of about + or - 10%. This in turn leads to sediment classification into at least two categories: sand and clay. Experiments to date have not had sufficient control of physical sampling relative to acoustic testing, and greater accuracies may be possible. The potential for indirectly measuring shear wave velocity and direclty inferring shear strength is explored and rejected for the short term. Shear information is contained in acoustic data but is too small to be measured. Shear strength can, in many cases, be deduced from acoustically measured density data, if a few cores are available for calibration. Further work is recommended to determine the true accuracy of acoustic measurements and to develop quantitative acoustic systems to satisfy Navy needs in seafloor geotechnical engineering. (Author).