3D frequency-domain waveform inversion using a row-projected Helmholtz solver

3D frequency-domain full waveform inversion relies on being able to efficiently solve the 3D Helmholtz equation. Iterative methods require sophisticated preconditioners because the Helmholtz matrix is typically indefinite. In the first part of the talk I review a preconditioning technique that is based on row-projections. Notable advantages of this preconditioner over existing ones are that it has low algorithmic complexity, is easily parallelizable and extendable to time-harmonic vector equations. In the second part of the talk I discuss how the row-projected solver can be used in the context of waveform inversion. Key aspects are: the use of block-iterative methods for multiple sources and adapting the accuracy of the solver.