Theoretical framework for geoacoustic inversion by adjoint method**Project supported by the Foundation of Key Laboratory of Marine Intelligent Equipment and System of Ministry of Education, China (Grant No. SJTU-MIES1908) and the National Natural Science Foundation of China (Grant No. 41775027).

Abstract

Traditional geoacoustic inversions are generally solved by matched-field processing in combination with meta-heuristic global searching algorithms which usually need massive computations. This paper proposes a new physical framework for geoacoustic retrievals. A parabolic approximation of wave equation with non-local boundary condition is used as the forward propagation model. The expressions of the corresponding tangent linear model and the adjoint operator are derived, respectively, by variational method. The analytical expressions for the gradient of the cost function with respect to the control variables can be formulated by the adjoint operator, which in turn can be used for optimization by the gradient-based method.