AMBIENT ACOUSTIC IMAGING IN HELIOSEISMOLOGY

The increasing availability of high spatial resolution data of velocit y and intensity variations on the Sun has stimulated the development o f helioseismological techniques that probe the solar interior in local ized regions. The techniques developed so far(1-4) have yielded inform ation on physical quantities (such as the flow velocity and magnetic f ield) below the surface, but are still far from providing a detailed p icture of local subsurface inhomogeneities. Here we report the develop ment and application of a new method for constructing three-dimensiona l solar images, utilizing acoustic noise (or stochastic P-mode oscilla tions) in the Sun. We treat a region of the solar surface as a phased array of acoustic sensors, which acts as a computational 'lens'; acous tic waves 'scattered' by local inhomogeneities, such as sunspots, are collected and summed in phase, based on the knowledge of how (on avera ge) they travel within the Sun. In this way, we are able to construct a three-dimensional image of a region of the solar interior.