Numerical Modeling of Acoustic Propagation in a Variable Shallow Water Waveguide

Abstract

Award Number: N00014-04-1-0148 http://www.apl.washington.edu LONG-TERM GOALSRandom variability in shallow water will induce variability in a propagating acoustic field. The general long-term goal of this research is to quantify how random variability in the ocean environment translates into random variability in the acoustic field and the associated signal processing algorithms. The specific long-term goal for the current funding cycle is to develop a predictive capability for the ambient noise notch in the presence of random ocean internal waves. OBJECTIVESThe scientific objective of current effort is to understand the effect of internal waves on the ambient noise notch. The ambient noise notch is a trough in the noise directivity pattern that is observed under certain circumstances. APPROACHThe technical approach to modeling the ambient noise notch is to combine sub models for acoustic propagation, shallow water internal waves, and ambient noise generation. The acoustic propagation sub model is based on the transport theory developed by Dozier and Tappert [1978] augmented to include bottom loss, an important consideration in shallow water. The internal wave sub model is based on a shallow water version of the Garrett-Munk spectrum developed by Henyey et al. [1997]. The validity of the combined model is tested by comparison to data from field experiments. In this testing, we are working with Dajun Tang of APL-UW and using data from the 2001 ASIAEX experiment. WORK COMPLETEDSub models for acoustic propagation, shallow water internal waves, and ambient noise generation were combined to develop a model for the ambient noise notch. In the present funding cycle, a more detailed testing of the model was completed. Model predictions agreed with experimental observations made over extended periods.