Tomographic inversion of geoacoustic properties in a range-dependent shallow-water environment

This paper presents a matched-field tomographic method to estimate the geoacoustic properties of the ocean bottom for a range-dependent medium in shallow water. The inversion method has been developed in order to interpret experimental data from the Haro Strait PRIMER sea trial. This experiment was carried out in June '96 and used low-frequency broadband signals that were received on three vertical line arrays. Inversion of the data is particularly difficult because of the complex bathymetry of the Haro Strait experimental site. For this inversion, a range-dependent ray code was developed to solve the forward problem, allowing an arbitrarily layered bottom environment. The inversion scheme is based on modeling the propagation time and the amplitude of the recorded data, and a simple new cost function is proposed. The signal ray paths are identified automatically using a simple process that compares calculated and measured travel times. Data from multiple source positions are used to invert the range dependence of the geoacoustic model. The environment is separated into segments, and within each segment the inversion is carried out layer by layer for a multilayer geoacoustic model. Starting with the topmost layer, the range-dependent thickness and sound speed are estimated via a Monte Carlo method. Inversion results are presented for synthetic and experimental data from the Haro Strait sea trial.