Abstract
The acoustic signal in the solar interior can be constructed based on the knowledge of how acoustic waves travel in the Sun, the time-distance relation (Chang et al. 1997). We discuss the basic principle and properties of the acoustic imaging and the update results with the TON data. The acoustic signal can be reconstructed with ingoing waves or outgiong waves. The time series of constructed acoustic signal contains information of both phase and intensity (Chou et al. 1998). The intensity information can be used to form the three-dimensional intensity image and absorption image of the solar interior. The absorption images show the absorption features in the active region. There exists a phase shift between the time series constructed with ingoing waves and outgoing waves. The phase shift is different in the active region and the quiet Sun. We construct a three-dimensional phase-shift map of the solar interior (Chen et al. 1998). The phase-shift features of the active region in the maps at the surface correlate well with magnetic fields. One can even identify the correlation between the phase-shift feature and weak magnetic field in the quiet Sun. The phase-shift maps show that travel time is shorter in the magnetic regions than in the quiet Sun. The three-dimensional intensity maps and phase maps can be used to study the subsurface structure of magnetic field. We also present the theoretical foundation of acoustic imaging.