Multipath Exploitation: Non-Line-of-Sight Target Relocation in Array-InSAR 3-D Imaging

With the development of synthetic aperture radar (SAR) 3-D imaging technology, urban 3-D imaging has been realized by unmanned aerial vehicle (UAV)-borne array interferometric SAR (array-InSAR), which enables simpler access to SAR data. However, in low-altitude SAR 3-D imaging of urban scenes, multipath effect is significant. In past studies, multipath signals have been mostly considered as a hindrance in interpretation, but they provide important clues for imaging hidden targets in non-line-of-sight (NLOS) regions. Based on this idea, this article studies the multipath exploitation in low-altitude UAV-borne array-InSAR 3-D imaging and realizes accurate imaging of NLOS targets. An improved 3-D imaging model suitable for low-altitude cases is introduced to achieve preliminary 3-D imaging. Subsequently, key planes are extracted from the original results and the 3-D multipath reachable area is analyzed. After obtaining the multipath mechanism of the NLOS targets, they can eventually be accurately relocated and imaged. Both the simulation and real-data experiments show that the proposed method can effectively 3-D imaging and relocate NLOS targets in urban canyons, with errors typically below 0.5 m. The imageable range in the direction of the ground range can be expanded by 41.62%, and the imageable 3-D area can be expanded by 76.57%, which realizes the NLOS information acquisition.