Verification of the Travel Time Measurement Technique and the Helioseismic Inversion Procedure for Sound Speed Using Artificial Data

摘要

We performed 3D numerical simulations of the solar surface wave field for thequiet Sun and for three models with different localized sound-speed variationsin the interior with: (i) deep, (ii) shallow, and (iii) two-layer structures.We used simulated data generated by two different codes which use the samestandard solar model as a background model, but utilize two differentintegration techniques and use different models of stochastic wave excitation.Acoustic travel times were measured from all data sets using the time-distancehelioseismology technique and compared with the ray theory predictions,frequently used for helioseismic travel-time inversions. It is found that themeasured travel-time shifts agree well with the ray theory in both cases withand without phase-speed filtering for the shallow and deep perturbations. Thistesting verifies the whole measuring-filtering-inversion procedure forsound-speed anomalies inside the Sun. It is shown, that the phase-speedfiltering, frequently used to improve the signal-to-noise ratio does notintroduce significant systematic errors. Results of the sound-speed inversionprocedure show good agreement with the background sound-speed profiles in allcases. Due to its smoothing nature, the inversion procedure overestimates soundspeed variations in areas with sharp gradients of the sound-speed profile.