Accelerated Computation of the Physical Optics Approximation for Near-Field Single- and Double-Bounces Backscattering

This article deals with the acceleration of the physical optics (PO) approximation for the backscattering computation in the near and far fields, for both single-bounce (SB) and double-bounce (DB) PO contributions. It is based on physical arguments, which allow us to apply either a closed-form expression (rapid calculation) or a numerical double integration to evaluate the scattered field from subsurfaces of a given mesh. The use of the closed-form expression is governed by two criteria, which must be extended to the bistatic case and also to the DB: the conventional Fraunhofer (related to the far-field zone) criterion and the chord error (related to the surface curvature) criterion. The proposed method is tested on a dihedral geometry.