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Title: Multi-frequency imagery based on the non-linearity of propagation. Applications to characterization of the seafloor.
Tutor: Marchal, Jacques
Keywords: underwater acoustics
nonlinear propagation
seafloor characterization
Multi Frequency Emission
Issue Date: 20-Sep-2013
Abstract: Classical acoustical surveying systems gather data about the seafloor usually on a narrow frequency bandwidth: a single system does not provide frequency diversity in the collected acoustic backscattered intensities. Gathering data at different frequencies has been revealed to be an interesting asset for sea floor characterization. At the present time, to collect multi- frequency information implies the use of different systems. Consequently, the acquired data are not perfectly matched in time and space, and their fusion is problematic. The feasibility of an original system that takes advantage of nonlinear propagation to achieve a multi-frequency source is presented. The principle is to generate a harmonic pulse with sufficient energy so that the saturation phenomenon emerges (Shooter et al., 1974). As a result, a single source generates a whole set of beams at the harmonic frequencies, and all these beams are perfectly superposed both in time and in space. First, a preliminary study in which a simplistic theoretical model based on a generalized Burgers’ equation is introduced. This was useful in the nonlinear propagation study and array sizing. Three sources conceived in our laboratory have been tested in pool facilities to study the multi-frequency emission feasibility. A special attention was focused on experimental development; however a comparison between numerical and experimental results is made. The research was then extended further to develop a Multi-frequency Side Scan Sonar prototype. A broadband receiver was realized within the purpose of one-day sea trials. A thorough analysis of the system and the future prospective are presented.
Research interests: Fascinated by science and passionate from the ability to share and communicate it, the candidate has played a diverse curriculum that would bring her closer to the world of research and disclosure. TEACHING-DIVULGATION: During the years of scientific activity has developed a growing awareness about the need to involve into the scientific study also the activity of teaching and communicating. Therefore for years her work is dedicated to various kinds of activities of outreach. - Mastery in the support and implementation of scientific-educational workshops - Good ability to collaborate and coordinate with a team working for the organization of events for the general public ( as Festival of Science ( GE ) , Science Week , etc .. ) SCIENTIFIC AREA: - Acoustic sources and receivers characterization; - Nonlinear acoustic propagation; - Hydrophones calibration; - Seafloor characterization; - Ultrasonic field characterization; - Evaluation of different sonar radiation on sea environment; - Study of underwater routes for the disposal of pipelines;

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