Global EM induction in the Earth:Inverse time-domain modelling based on the adjoint approach

摘要

We present a new method of inverse global electromagnetic (EM) induction modeling which is based on the effective evaluation of gradient of the misfit function in the space of model parameters using the solution of the adjoint problem. First, we present the rigorous formulations of the adjoint problem. Then, we apply the conjugate gradient (CG) or quasi-Newton (QN, also known as variable metrics) method to solve the non-linear inverse problem. The technique is tested on synthetic tests ranging from artificial checkerboard models excited by smooth sources to more realistic setups with respect to the upcoming SWARM mission.