The transient response of an atmospheric surface duct will be studied when the distance between receiving and transmitting end is arbitrarily chosen. The application of two integral transforms to the wave equation for the Fitzgerald vector--a Laplace transform in time and a two-dimensional Fourier transform in the horizontal coordinates in space-leads under consideration of initial, boundary and transition conditions, to an integral representation of the of the solution of the wave equation in transform space. Saddle point and Residue methods are used to compute the integral.