| Simulation methods of passive millimeter wave imaging are studied in this research,which are of great value for the study of passive millimeter wave radiation phenomenon of various targets.It is helpful to recognize the radiation characteristics of the target,explain some of the radiation phenomena,find the specific radiation patterns and judge the measured results.In addition,simulation in PMMW imaging is also beneficial to the parameter design of the radiometer system,with which the performance and the situation of the radiometer can be assessed conveniently.Also,it has become an effective supplement and substitute for real measurement,which can save time and cost.Therefore,simulation of PMMW imaging has recently begun to enter the research personnel's attention.Two aspects respectively computational efficiency and the application range are improved in this paper,which are as follows: 1.Space meshing ray tracing method for brightness temperature tracing was applied for the large-scale simulation in passive brightness temperature imaging with high accuracy.The model of brightness temperature tracing and retrieval was also established.The tracing process was described in detail to understand the improved method.Results indicated that the large-scale simulation with high distinguishability was efficiently realized by applying the proposed method.2.An improved model is proposed in this paper for rough surface scene simulation in millimeter wave imaging.And MBTT is suggested to consider the diffused reflection of rough surface.Our results indicate that the improved model is correct and effective in the simulation of the rough surface.Whereas,the discrimination of the brightness temperature tracing method is improved,with which different roughness of the same material can be clearly discriminated.3.An improved model is proposed for simulation of a scene with multi-layer rough surface in PMMW imaging.MBTT considers diffused transmission from the bottom layer.The improved model is correct and effective for simulating multi-layer rough surfaces.The applicable range of the brightness temperature tracing method is extended,and the scene with buried target can be simulated by the method.In addition,the effects of different RMS height,correlation length,and roughness of the dielectric constant of the rough surface are studied and analyzed.And the transmissivity of multi-layer rough surface is also studied.At last,the relationship between the thicknesses of the bottom layer and the brightness temperature is analyzed in the paper.4.The computational efficiency of MBTTM for multi-layer rough surface is improved by using the characteristics of Kirchhoff approximation method.In addition,a multi-layer densify algorithm is proposed to reduce the sub layer rays.The high efficiency of the proposed method has been verified by comparing with the traditional one. |
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