The adjoint method of optimal control for the acoustic monitoring of a shallow water environment

• Main Author: Meyer, Matthias
• Other Authors: Hermand, Jean-Pierre, Verbanck, Michel, Dubois, Frank, De Mol, Christine, Absil, Frans G. J., Asch, Mark
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: Universite Libre de Bruxelles 2007
• Subjects: Physique; Sciences de l'ingénieur; Underwater acoustics; Ocean tomography; Inversion (Geophysics); Deep-sea sounding; Acoustique sous-marine; Tomographie acoustique; Inversion (Géophysique); Sondage (Océanographie); shallow water acoustic tomography; geoacoustic inversion; adjoint method; maritime rapid environmental assessment; acoustic remote sensing; Arctic; Arctic Ocean
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210610; https://dipot.ulb.ac.be/dspace/bitstream/2013/210610/1/b48bf0c0-c96c-483c-b95f-dbad9a479158.txt; https://dipot.ulb.ac.be/dspace/bitstream/2013/210610/2/ca51bf40-8a4c-4956-ba94-43c2464d5b96.txt

Originally developed in the 1970s for the optimal control of systems governed by partial differential equations, the adjoint method has found several successful applications, e.g. in meteorology with large-scale 3D or 4D atmospheric data assimilation schemes, for carbon cycle data assimilation in biogeochemistry and climate research, or in oceanographic modelling with efficient adjoint codes of ocean general circulation models. Despite the variety of applications in these research fields, adjoint methods have only very recently drawn attention from the ocean acoustics community. In ocean acoustic tomography and geoacoustic inversion, where the inverse problem is to recover unknown acoustic properties of the water column and the seabed from acoustic transmission data, the solution approaches are typically based on travel time inversion or standard matched-field processing in combination with metaheuristics for global optimization. In order to complement the adjoint schemes already in use in meteorology and oceanography with an ocean acoustic component, this thesis is concerned with the development of the adjoint of a full-field acoustic propagation model for shallow water environments. In view of the increasing importance of global ocean observing systems such as the European Seas Observatory Network, the Arctic Ocean Observing System and Maritime Rapid Environmental Assessment (MREA) systems for defence and security applications, the adjoint of an ocean acoustic propagation model can become an integral part of a coupled oceanographic and acoustic data assimilation scheme in the future. Given the acoustic pressure field measured on a vertical hydrophone array and a modelled replica field that is calculated for a specific parametrization of the environment, the developed adjoint model backpropagates the mismatch (residual) between the measured and predicted field from the receiver array towards the source. The backpropagated error field is then converted into an estimate of the exact gradient of the objective ...