An acoustic source, in conjunction with an array of acoustic receivers in a nearby isovelocity region, can be used as a probe to measure the ocean surface. F. M. Labianca [J. Acoust. Soc. Am. 67, 1567–1577 (1980)] has developed a procedure for estimating the ocean‐surface directional spectrum by this means. The problem he solves is typically called inverse scattering. This paper addresses the issue of what region of the ocean surface is being sampled in his procedure. It is desirable that the sampled region be sufficiently confined that the assumption of spatial homogeneity may be safely made, otherwise the directional spectrum has no meaning. It is proved in this paper that, for a given receiver, the region sampled by Labianca’s procedure is a small circle on the ocean surface, with center over the source and radius equal to the horizontal range between source and receiver. The proof is subject to a constraint on the wavelength of the source.