Mobile Radar Mapping - Subcentimeter SAR Imaging of Roads

In this paper, we present a strategy for focusing ultrahigh-resolution synthetic aperture radar (SAR) data for mobile radar mapping. We illustrate the related theoretical background and required extensions on the imaging method based on backprojection techniques. The influence of potential errors in estimating a correct geometry with respect to the imaging quality is investigated in detail by point target simulations. As backprojection techniques require precise knowledge of the topography in close range, the new strategy instantly uses the GPS/INS data of the trajectory to define a suitable digital elevation model of the illuminated scene. We have tested the strategy by driving on conventional roads with an active frequency-modulated continuous wave radar system operating at 300 GHz. Different reference targets were placed in the scene, and the accuracy of the method was evaluated. The results experimentally reveal that the lower terahertz band is capable of subcentime ter SAR imaging in mobile mapping scenarios at very high quality. We have shown that narrow cracks in the asphalt of roads can be detected and fine-scale objects on millimeter size can be displayed. Geometric distortions in the SAR images are significantly reduced allowing the measurements of infrastructure. The output data can at last be transferred to the conventional 3-D Point Cloud Software for further processing.