The Effects of Sediment Properties on Low Frequency Acoustic Propagation

Abstract

Our work focuses on understanding the frequency and depth dependence of compressional wave attenuation and developing new inversion schemes for shear wave properties. Our initial investigations have indicated that water-borne acoustic arrival properties such as their Airy Phase are sensitive to sediment shear properties. Our major emphasis this year has been to develop and test inversion schemes for simultaneous estimation of compressional and shear properties. The long term goals of our research are to: • Improve inversion schemes for the estimation of sediment geoacoustic properties using low frequency broadband acoustic signals at short and long ranges. • Continue fine-tuning our Shear Measurement System, recently developed under a DURIP grant, for short range interface/Scholte wave-based inversions for shear properties. • Adapt our long range sediment tomography technique for compressional and shear wave speeds, and attenuation profiles utilizing the broadband Combustive Sound Source (CSS) developed at the Applied Research Laboratories (ARL), University of Texas. OBJECTIVES We propose to pursue the long term goals listed above by executing the objectives listed below. A. Engineering tests: A shear measurement system is recently being developed and tested at URI as part of a DURIP grant. Additional sensors will be integrated into this system and further engineering tests will be conducted to make the system ready for deployment during future ONR field tests. The tasks associated with this objective can be summarized as follows: a. Conduct a number of engineering tests on land and in the shallow waters of Narragansett Bay of the URI Shear Measurement System. b. Enhance the capability of the system by integrating and testing 3-axis geophones. c. Test the SHRU receiving system with both hydrophones and geophones.