Abstract
Over the past 25 years, there has been significant research activity in development and application of methods for inverting acoustical field data to estimate parameters of geoacoustic models of the ocean bottom. Although the performance of various geoacoustic inversion methods has been benchmarked on simulated data, their performance with experimental data remains an open question. This article constitutes the first attempt of an experimental benchmark of geoacoustic inversion methods. To do so, the article focuses on data from experiments carried out at a common site during the Shallow Water 2006 (SW06) experiment. The contribution of the article is twofold. First, the article provides an overview of experimental inversion methods and results obtained with SW06 data. Second, the article proposes and uses quantitative metrics to assess the experimental performance of inversion methods. From a sonar performance point of view, the benchmark shows that no particular geoacoustic inversion method is definitely better than any other of the ones that were tested. All the inversion methods generated adequate sound-speed profiles, but only a few methods estimated attenuation and density. Also, acoustical field prediction performance drastically reduces with range for all geoacoustic models, and this performance loss dominates over intermodel variability. Overall, the benchmark covers the two main objectives of geoacoustic inversion: obtaining geophysical information about the seabed, and/or predicting acoustic propagation in a given area.
Highlights
F OR the past three decades there has been renewed focus among researchers in underwater acoustics on sound propagation in shallow water
The hypothesis in this article is that the experiments carried out in Shallow Water 2006 (SW06) form the basis of an experimental benchmark for geoacoustic inversion methods, and the comparison of the various estimated models using appropriate metrics can be used to address the questions about inversion performance
1) Are the inversion methods capable of generating geoacoustic models that are realistic and useful representations of the real ocean bottom? 2) What are the limitations of each inversion method? Which geoacoustic model parameters are well estimated, and which ones are estimated with limited success? 3) Which model parameters have the greatest impact on the acoustical field in the water? apart from the comparison of inversion performance, analysis of results of an experimental benchmark provides other information about the capabilities of present-day geoacoustic inversion methods
Summary
F OR the past three decades there has been renewed focus among researchers in underwater acoustics on sound propagation in shallow water. Participants were tasked to invert the geoacoustic model parameters of the test case environments, including sound speed, attenuation, and density of the layered structures, and determine a measure of the uncertainty of the estimates The results of both workshops indicated that the inversion methods were capable of generating highly accurate representations of the true geoacoustic models that were used in the test cases. Taken as a whole the results derived from SW06 experimental data provide new information about the dispersion of sound speed and attenuation in the marine sediments at the experimental site over a broad frequency band spanning nearly four decades from ∼50 Hz to ∼60 kHz. The hypothesis in this article is that the experiments carried out in SW06 form the basis of an experimental benchmark for geoacoustic inversion methods, and the comparison of the various estimated models using appropriate metrics can be used to address the questions about inversion performance.
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