3aUW2. Recent shallow-water acoustic measurements of sound transmission, reverberation, and coherence.

Session: Wednesday Morning, May 15

Time: 8:35

Author: William M. Carey
Location: Adv. Res. Projects Agency, 3701 N. Fairfax Dr., Arlington, VA 22203
Author: Peter Cable
Author: Mike Steele
Location: BBN Systems and Technol., Arlington, VA 22209


Recent experiments performed in the shallow waters (100 m deep) of the Gulf of Mexico, East Continental Shelf of America, and the Korean Straits under the condition of downward refraction with sandy--silty clays are discussed. These experiments were performed with both explosive, air gun, and continuous sources covering the 100-Hz to 1-kHz frequency range. The receivers were both horizontal arrays on the bottom and vertical arrays which spanned the water column. Precise navigation was employed to eliminate range uncertainties and all measurement systems were calibrated to a traceable standard. The results are presented in the categories of sound transmission, reverberation, and coherence. Sound transmission results were found to generally agree with wave-theoretic numerical codes and shear was not found to be important. The reverberation was found to have a frequency-dependent characteristic consistent with sediment layering. Coherence lengths are estimated from array signal gain measurements in the midfrequency range and compared to previous measurements in both deep and shallow water. Results were found to be influenced by a variety of factors such as water column variations. Estimates of the importance of these factors under downward refracting conditions will be made and extended to other sound velocity profiles.

from ASA 131st Meeting, Indianapolis, May 1996