Imaging wave-penetrable objects in a finite depth ocean

We extend the direct sampling method proposed in Ito et al. (2012) [13] to image a wave-penetrable inhomogeneous medium in a 3D waveguide. Incidences and receivers are available only on part of the surface of a cylinder. The proposed method is basically direct and does not involve any matrix inversions or optimizations, thus computationally very cheap and efficient. Numerical simulations are presented to show the feasibility and effectiveness of the method for acoustic detection in a 3D waveguide. The method is applicable with a few scattered fields corresponding to only one or two incident waves, and is very robust against noise.