Improved delay-and-sum algorithm for ground-penetrating radar imaging considering refraction in multi-layered media

Abstract

While investigating concrete structures using ground-penetrating radar (GPR), electromagnetic (EM) waves typically propagate through multi-layered refractive media. However, existing image-focusing methods that account for refraction are limited to two-layer cases and often rely on approximations of propagation paths, potentially degrading accuracy in multi-layer cases. This study proposes an improved delay-and-sum algorithm (DSA) considering EM wave refraction in planar multi-layered media. The proposed DSA overcomes the limitations of existing methods by addressing both the constraints of two-layer cases and the reliance on propagation path approximations, thus enabling high-accuracy image focusing in cases involving three or more layers. To achieve this, the wave propagation path is formulated for planar multi-layered media, and the DSA is improved to incorporate the numerical solutions of these refracted paths. The improved DSA is validated through numerical simulations of asphalt pavement and concrete structures, as well as a GPR survey of a reinforced concrete specimen. Results demonstrate a significant enhancement in image-focusing quality compared to conventional DSA.