Point-source excitation of the density contrast wedge: Perturbation for nearly equal sound speeds

The extension of the Biot-Tolstoy exact time-domain solution to the density contrast wedge is used to develop an iterative procedure that facilitates construction of the first-order perturbation of the exterior field with res pect to distinct wave speed for a point source, which is either smoothly sw itched on and off within a finite time or is oscillatory for all time. In b oth cases, this perturbation field is symmetric with respect to the source and field points and appears as an integral over the wedge involving the is ovelocity solution for the interior region. The 'geometrical acoustics' com ponents are simplified for 'rational' wedge angles in the switch-on/off cas e and estimated in the far field in the oscillatory case to be generated by a ray passing through the wedge, possibly with internal reflection.