Single receiver inversion in shallow water

International audienceLow frequency propagation (0-200 Hz) in shallow water (10-400 m) is described by modal theory. When using a single receiver, one challenge is to extract information about the modes in order to localize an acoustic source and/or characterize the environment. Indeed, when source/receiver distance is about a few kilometers to a dozen of kilometers, modes are overlapped in time and in frequency. This article presents a method for extracting modal travel times using a single receiver without any a priori knowledge of the environment. Adaptive signal processing is applied to compensate for modal dispersion, using time and frequency warping transformations adapted to the physics of propagation. Warping allows to filter each modal contribution by overcoming inherent limitations of time-frequency representations. Once each modal component is filtered, high resolution estimation of modal travel times is performed using reallocated spectrogram. The extracted modal travel times are robust features of propagation, as they can straightforwardly be linked to modal group velocities. This article presents an inversion scheme based on these features. It is successfully applied on experimental data recorded in an ultrasonic tank