Immersion depth estimation using spectrograms displaying Lloyd's mirror patterns

Lloyd's mirror effect has been used in the past for estimating the location parameters of an underwater target, under the hypothesis of constant speed of sound, in which the sound propagates along straight lines. However, as the sound speed depends on the water temperature, which typically varies with depth, the sound propagation paths become curved. In this paper, we use a ray tracing method for computing the time delays along the direct and the reflected signals under different sound speed profiles in a shallow water environment. The time delays are used to synthesize a sensor signal containing multipath interference. The location parameter of the target can be estimated by matching a measured spectrogram against libraries of simulated spectrograms. In the experiments we illustrate the estimation process and the robustness against uncertainty in the sound speed profiles among the libraries.