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

TL;DR

This study validates helioseismic travel time measurement and inversion techniques for detecting sound-speed variations inside the Sun using artificial data, confirming their accuracy and limitations.

Contribution

It provides a comprehensive verification of the travel time measurement and inversion procedures with artificial data, including effects of phase-speed filtering.

Findings

Travel time measurements agree with ray theory predictions.

Phase-speed filtering does not cause significant systematic errors.

Inversion results match background sound-speed profiles well.

Abstract

We performed 3D numerical simulations of the solar surface wave field for the quiet Sun and for three models with different localized sound-speed variations in the interior with: (i) deep, (ii) shallow, and (iii) two-layer structures. We used simulated data generated by two different codes which use the same standard solar model as a background model, but utilize two different integration techniques and use different models of stochastic wave excitation. Acoustic travel times were measured from all data sets using the time-distance helioseismology technique and compared with the ray theory predictions, frequently used for helioseismic travel-time inversions. It is found that the measured travel-time shifts agree well with the ray theory in both cases with and without phase-speed filtering for the shallow and deep perturbations. This testing verifies the whole measuring-filtering-inversion procedure for sound-speed anomalies inside the Sun. It is shown, that the phase-speed filtering, frequently used to improve the signal-to-noise ratio does not introduce significant systematic errors. Results of the sound-speed inversion procedure show good agreement with the background sound-speed profiles in all cases. Due to its smoothing nature, the inversion procedure overestimates sound speed variations in areas with sharp gradients of the sound-speed profile.