INFLUENCE OF ACOUSTIC SOURCE DENSITY ON CROSS-CORRELATED SIGNALS: IMPLICATIONS FOR AMPLITUDE-BASED TOMOGRAPHY IN HELIOSEISMOLOGY

We present new results from the numerical simulations of cross-correlated helioseismic data in a two-dimensional quiet non-magnetic solar subphotosphere for studying the effects of spatiotemporal density of solar acoustic sources on signal quality. Although the signal-to-noise level of helioseismic signals can be improved by data averaging, our results show that there exists a threshold above which this change in data quality is largely independent of the density of the acoustic sources. We also demonstrate that if the source density is below this threshold, significant data artifacts may arise depending on the source location relative to the two observation points at which cross-correlation is performed. Our numerical results therefore show that the density of the acoustic sources is a key, previously unidentified parameter that influences the quality and amplitude of cross-correlated helioseismic signals. We conclude that the identification of this source parameter is important for developing helioseismic tomography beyond travel-time-based methods, namely by modeling amplitudes.