  This paper is concerned with the inverse problem of time-harmonic acoustic
scattering by an unbounded, locally rough interface which is assumed to be a
local perturbation of a plane. The purpose of this paper is to recover the
local perturbation of the interface from the near-field measurement given on a
straight line segment with a finite distance above the interface and generated
by point sources. Precisely, we propose a novel version of the linear sampling
method to recover the location and shape of the local perturbation of the
interface numerically. Our method is based on a modified near-field operator
equation associated with a special rough surface, constructed by reformulating
the forward scattering problem into an equivalent integral equation formulation
in a bounded domain, leading to a fast imaging algorithm. Numerical experiments
are presented to illustrate the effectiveness of the imaging method.
