Multilevel Physical Optics Algorithm for Near-Field Double-Bounce Scattering

A fast algorithm for the evaluation of the double-bounce (DB) contributions to the physical optics scattering integrals, over a range of aspect angles and frequencies, is presented. The work extends the preceding far-field algorithm, to encompass three-dimensional and near-field scenarios. The algorithm relies on multilevel sampling and interpolation of phase- and amplitude-compensated contributions of subdomain pairs. A particular design of the phase- and amplitude-compensation functions and sampling grids, tailored to the DB near-field case, is presented. The improved performance and error controllability are demonstrated via representative examples.