Travel-time sensitivity kernels for time-distance helioseismology

The forward problem of time-distance helioseismology is to compute travel-time perturbations which result from perturbations to a solar model. We present a new and physically motivated general framework for calculations of the sensitivity of travel-times to small local perturbations. Our starting point is a description of the wavefield excited by distributed random sources. We employ the first Born approximation to model scattering from local inhomogeneities. We give a clear definition of travel-time perturbation, which allows a connection between observations and theory. In this framework travel-time sensitivity kernels depend explicitly on the details of the measurement procedure.