Full waveform inversion for time-distance helioseismology

Shravan Hanasoge, Jeroen Tromp

Research output: Contribution to journalArticle

Abstract

Inferring interior properties of the Sun from photospheric measurements of the seismic wavefield constitutes the helioseismic inverse problem. Deviations in seismic measurements (such as wave travel times) from their fiducial values estimated for a given model of the solar interior imply that the model is inaccurate. Contemporary inversions in local helioseismology assume that properties of the solar interior are linearly related to measured travel-time deviations. It is widely known, however, that this assumption is invalid for sunspots and active regions and is likely for supergranular flows. Here, we introduce nonlinear optimization, executed iteratively, as a means of inverting for the subsurface structure of large-amplitude perturbations. Defining the penalty functional as the L 2 norm of wave travel-time deviations, we compute the total misfit gradient of this functional with respect to the relevant model parameters at each iteration around the corresponding model. The model is successively improved using either steepest descent, conjugate gradient, or the quasi-Newton limited-memory Broyden-Fletcher-Goldfarb-Shanno algorithm. Performing nonlinear iterations requires privileging pixels (such as those in the near field of the scatterer), a practice that is not compliant with the standard assumption of translational invariance. Measurements for these inversions, although similar in principle to those used in time-distance helioseismology, require some retooling. For the sake of simplicity in illustrating the method, we consider a two-dimensional inverse problem with only a sound-speed perturbation.

Original languageEnglish (US)
Article number69
JournalAstrophysical Journal
Volume784
Issue number1
DOIs
StatePublished - Mar 20 2014

Fingerprint

helioseismology
waveforms
inversions
travel time
travel
solar interior
inverse problem
deviation
iteration
perturbation
gradients
descent
sunspots
penalties
sunspot
norms
newton
invariance
near fields
pixel

Keywords

  • helioseismology - waves
  • Sun

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics
  • Nuclear and High Energy Physics

Cite this

Full waveform inversion for time-distance helioseismology. / Hanasoge, Shravan; Tromp, Jeroen.

In: Astrophysical Journal, Vol. 784, No. 1, 69, 20.03.2014.

Research output: Contribution to journalArticle

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