The underwater acoustic propagation path between transmit and receive planar arrays via the surface of the ocean is treated as a linear, time-varying, random WSSUS communication channel. The random, time-varying, transfer function of the ocean’s surface is derived for a bistatic geometry using a generalized Kirchhoff approach. The result for the bistatic configuration can then be easily reduced to either the specular or backscatter geometries. The generalized Kirchhoff approach uses a Fresnel corrected Kirchhoff integral, no small slope approximation, and the Rayleigh hypothesis that the scattered acoustic pressure field can be represented as a superposition of plane waves traveling in many different directions. The transfer function obtained in this paper is shown to contain additional terms when compared with those expressions for scattered acoustic pressure previously derived by the classical Kirchhoff approach, especially for the specular and backscatter geometries.