Jean Kormann

Modelling seismic oceanography experiments by using first- and second-order Complex Frequency Shifted Perfectly Matched Layers

This work investigates the ability of modelling seismic oceanography experiments by using underwater acoustic propagation equations. Seismic oceanography tries to retrieve the fine structure of the ocean water masses by processing the acoustic waves reflected in the low-contrast interfaces of fronts, eddies, internal waves or thermohaline intrusions. Since the reflectivity of such interfaces is of order 10 ―3 ―10 ―4 , the absorption capability of the numerical boundaries becomes crucial. Complex Frequency Shifted offers a better alternative to classical Perfectly Matched Layer formulation, but has not yet been extended to acoustic equations. Here, first- and second-order Complex Frequency Shifted Perfectly Matched Layers equations are proposed which can provide reflection coefficients of order 10 ―5 . Therefore, a numerical Finite-Difference Time-Domain (FDTD) scheme combined with the proposed CFS-PML equations is able to model such experiments.

Synthetic Modeling for an Acoustic Exploration System for Physical Oceanography

AbstractMarine multichannel seismic (MCS) data, used to obtain structural reflection images of the earth’s subsurface, can also be used in physical oceanography exploration. This method provides vertical and lateral resolutions of O(10–100) m, covering the existing observational gap in oceanic exploration. All MCS data used so far in physical oceanography studies have been acquired using conventional seismic instrumentation originally designed for geological exploration. This work presents the proof of concept of an alternative MCS system that is better adapted to physical oceanography and has two goals: 1) to have an environmentally low-impact acoustic source to minimize any potential disturbance to marine life and 2) to be light and portable, thus being installed on midsize oceanographic vessels. The synthetic experiments simulate the main variables of the source, shooting, and streamer involved in the MCS technique. The proposed system utilizes a 5-s-long exponential chirp source of 208 dB relative to ...