Passive Millimeter-Wave Polarimetric Imaging for Buried Metallic Target Detection: Modeling, Simulation, and Experimental Validation

Post-war legacy buried explosive ordnance poses a severe threat to life safety, making humanitarian demining a crucial part of China's Global Security Initiative. With its unique capability to penetrate shallow subsurface while offering high-resolution and intuitive imaging, passive millimeter-wave (PMMW) imaging has emerged as a promising new approach for detecting buried metallic targets. However, only a few exploratory measurement experiments have been reported, and the millimeter-wave radiation polarization characteristics of buried metallic targets remain unexplored. This article is the first to conduct an investigation and evaluation of the Ka-band PMMW polarimetric imaging detection performance of buried metallic targets through modeling, simulation, and experiments. A millimeter-wave brightness temperature (TB) model is established to describe the radiation from buried metallic targets into free space. Using the ray-tracing method, we simulated and predicted the TB images under four linear polarization states (horizontal, vertical, 45°, and 135°). Furthermore, we analyzed the characteristics of eight polarimetric feature parameter images, including Stokes parameters. Outdoor polarimetric imaging experiments in a sandy terrain environment were conducted to validate the theoretical and simulation results. The detection performance was quantitatively evaluated using receiver operating characteristic curves. The findings indicate that vertical polarization gives the highest image contrast and is therefore the most suitable polarization for detection. Preliminary results from additional imaging experiments in five typical covered scenarios (e.g., leaf litter and shallow grass) further confirmed the feasibility in real-world applications where targets are covered by relatively shallow layers. This study provides a significant foundation for the design of PMMW polarimetric detection systems and the development of detection methods for buried metallic targets.