A critical review of geoacoustic inversion: What does it really tell us about the ocean bottom?

Abstract

Estimation of parameters of geoacoustic models from acoustic field data has been a central theme in acoustical oceanography over the past three decades. Highly efficient numerical techniques based on Bayesian inference have been developed that provide estimates of geoacoustic model parameters and their uncertainties. However, the methods are model-based, requiring accurate knowledge of the acoustic propagation conditions in the ocean to carry out the inversion. More recent research has revealed fundamental limitations of model-based inversion methods in conditions of unknown temporal and spatial variations in the water. In addition, the inversions can generate only effective models of the true structure of the ocean bottom, which are generally highly variable over relatively small spatial scales. There are other questions about the theory for sound propagation in porous sediment media that raise doubt about the validity of inversion results. In most inversions, a visco-elastic theory is used, but is this correct? This paper reviews successes and failures of geoacoustic inversion to understand the limitation of model-based methods. Research directions are suggested in conclusion that show promise for development of new approaches. [Work supported by ONR.]