| Passive millimeter wave imaging system works making use of the electromagnetic thermal emission of the subject and reflected thermal signals from the background. Passive millimeter wave imaging, in comparision to visible or infrared imaging, has great potential advantage of imaging through fog, clouds, smoke, sandstorms and other poor weather conditions. Current imaging systems relied on mechanical scanning of a single beam have problems of low spatial resolution and poor sensitivity. During the past several years, due to significant advances in the development of solid state components and high-speed signal processing technology, multi-beam array imaging systems, which promise an increase in sensitivity and resolution, have received considerable interest in both the military and civilian applications.Firstly, the principle and theory of passive millimeter-wave imaging are discussed and the development and application of it are introduced; secondly, imaging model of passive millimeter-wave imaging system is analyzed combining with the principle of millimeter-wave image system, then based on the model, imaging results are obtained through the simulation experiments; thirdly, the spatial variation characteristics of the system are described quantitatively and the mathematical model of geometric distortion is set up based on the research of the mechanism of passive millimeter wave imaging, then the spherical projection transformation is proposed used to correct the geometric distortion of passive millimeter wave image, at the same time, the way of estimating the PSF and the complete process of super-resolution imaging are proposed, laying the foundation for follow-up image processing; lastly, starting with degradation cause of millimeter-wave image, some image restoration methods and super-resolution algorithms are used in passive millimeter-wave image processing of the spatial variation model, and an new improved method using nonlinear extrapolation in frequency space is proposed. |
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