Propagation and Ambient Noise Studies for Ocean Acoustics Applications
PORTLAND STATE UNIV OR DEPT OF ELECTRICAL AND COMPUTER ENGINEERING
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Ocean ambient noise has been studied for decades. Much of the interest has been on determining the impact of noise on sonar performance. In this context, noise has generally been considered a nuisance and the research focus has been on methods to measure and predict ocean noise. In this project, the emphasis has been shifted to how ocean noise can be exploited. Results over the past several years have shown that breaking wave noise can be used for remote sensing the environment. There are several advantages to passive remote sensing including simple measurement requirements and the minimal environmental impact. Advancements in the noise-based remote sensing methodologies will be described in this annual report. In particular, one of the techniques being investigated uses noise as a type of passive fathometer or sub-bottom profiler and another uses noise to estimate the seabed reflectivity i.e., bottom loss. Both techniques lead to better characterization of the seabed. Knowing the seabed properties is important to predict sound propagation in the ocean and therefore predicting sonar system performance. Eventually, these methods can lead to new surveying techniques that might be used to update the Low Frequency Bottom Loss LFBL or High Frequency Bottom Loss HFBL databases. LFBL and HFBL are databases that the Naval Oceanographic Office NAVO maintains and updates and are used for sonar performance prediction as part of the navy s tactical decision aids.