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A time-distance helioseismic technique, similar to the one used by Ilonidiset al (2011), is applied to two independent numerical models of subsurfacesound-speed perturbations to determine the spatial resolution and accuracy ofphase travel time shift measurements. The technique is also used to examinepre-emergence signatures of several active regions observed by the MichelsonDoppler Imager (MDI) and the Helioseismic Magnetic Imager (HMI). In the contextof similar measurements of quiet sun regions, three of the five studied activeregions show strong phase travel time shifts several hours prior to emergence.These results form the basis of a discussion of noise in the derived phasetravel time maps and possible criteria to distinguish between true and falsepositive detection of emerging flux.

Analysis of Time-Distance Helioseismology for Detection of Emerging Active Regions