Research On Passive Millimeter Wave Simulation And Experiment Of Rough Surface

As a new target detection method,passive millimeter-wave(PMMW)imaging is used in the fields of human security,military detection,terrain mapping modeling and firefighting.Therefore,it has great research value and urgent application needs.Through the radiation imaging simulation of the observation scene,it is not only beneficial to deep understand the PMMW image from the physical principle level,but also has guiding significance for the interpretation of the measured data and the design of the new imaging system.At present,research work usually considers the object as a smooth surface to conduct ray tracing calculation and analysis.However,many surfaces of the object no longer belong to smooth surfaces in the millimeter-wave band,and the multidirectional radiations caused by the scattering of rough surface cannot be ignored.Based on this,this thesis conducts PMMW imaging simulation and experimental research for rough surfaces.The main works includes:(1)Expounded the calculation model of brightness and emissivity of smooth surface and rough surface.Analyzed the influence of surface roughness on emissivity and self-illumination temperature.The results show that the emissivity and brightness temperature of different roughness levels are significantly different,so it is necessary to consider roughness when establishing the calculation model of brightness temperature.(2)Established a rough surface imaging simulation calculation model based on multidirectional ray tracing.Aiming at the discretization problem of the scattering direction of rough surface in the whole space,this thesis proposed a multi-directional ray division method based on the density characteristics of the scattering pattern.For the problem of exponential growth of computational complexity caused by multi-directional ray tracing,this thesis utilized the two-in-one bounding box algorithm to accelerate the calculation process.(3)Carried out several outdoor scene simulations and experimental verification.Analyzed the apparent brightness temperature difference of different rough surfaces by simulation calculation model.For the rough surface scenes such as grassland,sandy land and bare soil,this thesis compared the simulation image of smooth surface model,the simulation image of rough surface model and the measured image.The results show that the new model considering roughness has the better consistency and the smaller error with the measured data.The model and method proposed in this thesis make up the shortcomings of PMMW imaging simulation of random rough surface targets.For more types of rough surfaces,it is necessary to carry out further research in the future.