A Technique for Measuring Bottom Velocity of a Water-Glycerine Interface Utilizing a Normal Specific Acoustic Impedance Measurement.
PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB
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A two-fluid experiment using water and glycerine was conducted to test the validity of a new theory for predicting sound speeds in the ocean bottom. The theory, developed by D. C. Stickler of this laboratory, predicts a peak near the critical angle in the normal specific acoustic impedance versus angle of incidence curve at the ocean bottom interface. A study of the shift in this impedance peak as a function of source frequency or source height above the interface leads to an estimate of the critical angle and, thus, the bottom velocity. The investigation yielded results which strongly support the theoretical expectations. The impedance peak as well as all the predicted trends in the shift of this peak were measured. A systematic 5 deg - 6 deg discrepancy in the location of the impedance peak was found to exist between measured and theoretical data. Numerous possible sources of error were investigated. The lateral wave at the water-glycerine interface was also observed and photographed. A brief investigation of the lateral wave suggested an intensity decay rate with range of 1RR.