The adjoint method applied to time-distance helioseismology
Abstract
For a given misfit function, a specified optimality measure of a model, its gradient describes the manner in which one may alter properties of the system to march towards a stationary point. The adjoint method, arising from partial-differential-equation-constrained optimization, describes a means of extracting derivatives of a misfit function with respect to model parameters through finite computation. It relies on the accurate calculation of wavefields that are driven by two types of sources, namely the average wave-excitation spectrum, resulting in the forward wavefield, and differences between predictions and observations, resulting in an adjoint wavefield. All sensitivity kernels relevant to a given measurement emerge directly from the evaluation of an interaction integral involving these wavefields. The technique facilitates computation of sensitivity kernels relative to three-dimensional heterogeneous background models with magnetic fields, thereby paving the way for non-linear iterative inversions. We present flow, sound-speed and magnetic-field kernels.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMSH51B2002H
- Keywords:
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- 7290 SEISMOLOGY / Computational seismology;
- 7522 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Helioseismology;
- Data Assimilation