| The material evidence search is very important for the correct analysis of the case and the determination of the facts of the case.In most modern cases,especially in explosive cases,the on-site environment is very complicated.The use of drones for physical evidence search can greatly improve search efficiency and has become one of the main means of material evidence search.However,the cameras of traditional light and small drones usually only use intensity imaging,and their imaging contrast is low,which is easily affected by environmental conditions such as forest land,haze and complex terrain.It is difficult to achieve rapid search and accurate identification of physical evidence.Polarization imaging not only improves imaging contrast,but also increases imaging distance in soot and smog environments;In addition,long-wave infrared imaging effectively identifies targets in lowlight or night environments.Therefore,this paper proposes an imaging detection scheme that combines visible light polarization with long-wave infrared for biometric search and recognition.Moreover,the two-speed zoom optical imaging method is adopted,and in the short focus mode,the large field of view is quickly searched for the target,and in the telephoto mode,the high resolution is accurately recognized.The system is compact and suitable for use on unmanned aerial platforms.This paper first investigates the research status of polarization imaging systems at home and abroad,and summarizes the advantages and disadvantages of different polarization imaging methods;Then the basic theory of polarization imaging and two-speed zoom optical system design is deeply studied.Based on the imaging requirements of UAV-borne material evidence search,the imaging optical system index parameters were calculated and analyzed,and the visible two-lens zoom polarization imaging system and the long-wave infrared twospeed zoom imaging system were designed respectively.Among them,visible light polarization imaging system is a large field of view large aperture structure,F number is 1.8 and 2.7,the field of view is 62 ° and 30 °,the modulation transfer function is better than 0.38 at the Nyquist frequency 145 lp / mm,Image quality meets usage requirements,the visible light system is received by the micro-polarization detector,and the four stocks vectors of the target are simultaneously acquired,and the target polarization degree image is obtained through fusion processing.At the same time,this paper also analyzes the defocus range of the visible light system,adjusts the position of the image plane by moving the zooming group,and realizes clear imaging under the condition of flying height of 3m~10m;Long-wave infrared imaging optical system with full field of view of 29° and 15°,respectively,and the F number is 1.1.The modulation transfer function is better than 0.45 at the Nyquist frequency of 30 lp/mm.The image surface shift caused by the object distance and temperature change is analyzed,and the moving image surface compensation method is used to compensate the image surface defocus,and the image quality satisfies the use requirement.The results of tolerance analysis show that the tolerance distribution of visible light polarization imaging system and long-wave infrared imaging system is reasonable,which meets the requirements of system processing and assembly.Finally,by setting up an experimental platform,the typical physical evidence target is photographed to obtain the target visible light polarization and long-wave infrared image.The experimental results show that the target of visible light polarization and long-wave infrared dual-band detection can improve the target imaging contrast under complex conditions,highlighting the target texture,material and shape,and further improve the accuracy of target detection and recognition,and provide an effective means for material evidence search at the scene of a crime in a complex environment. |
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