Orientation Estimation of Surface Cracks in Metals Based on Intensity Maximization of Polarimetric Circular Synthetic Aperture Radar Images

In this article, we propose a novel method of estimation of crack orientation on a metallic surface using linearly polarized circular synthetic aperture radar (SAR) imaging. We modeled a crack using a thin linear scatterer and considered the rotation of polarization basis vectors that were designed to match a predefined orientation vector corresponding to a temporary estimate of the orientation of the linear scatterer. The radar image intensity was expected to be a maximum when the specified orientation vector exactly matched the true scatterer orientation angle; therefore, to estimate the orientation of the scatterer, we aimed to obtain the maximum intensity of the image by varying the orientation vector. We validated the proposed scheme of estimation via a numerical electromagnetic simulation using the method of moments (MoM) and laboratory measurements carried out in an anechoic chamber. In this experiment, a metallic plate with slits was used as a simple surface crack model and the root-mean-square error and maximum error of the angular estimation were 1.9° and 5.1°, respectively.