Research On Key Techniques For Medium Wave Infrared Target Detection Device

With the extensive application of infrared technology in the military field,infrared imaging guidance technology has become a research hotspot in the world.Infrared imaging guidance technology has the advantages of all-weather guidance ability,high detection sensitivity and spatial resolution,strong roughness against noise,and can achieve the independent capture,identification and tracking of the target in the complex background,which has become an important technical method for developing the precision-guided weapons in the world.Based on the specific national defense project,this paper has carried out the research work on the medium wave infrared target detection device applied to the infrared imaging guidance.The key techniques,which contains the athermal design of infrared optical system,the quantitative analysis and suppression of narcissus,testing and evaluation of the imaging quality,are researched in this paper.In order to ensure that the infrared optical system has excellent thermal stability at the temperature range of-30?~70?,the influence of temperature change on the structural parameters and performance of the optical system is analyzed,and the athermal design method of thin lenses in contact of infrared optical system based on athermal chart is discussed.On the basis of this,the athermal design method of thick lenses spaced apart of infrared optical system is studied,and the Petzval and Cooke structure and their complex structures are analyzed based on athermal chart,and the mathematical models for solving the initial structural parameters of the optical system are proposed,at the same time,a method for calculating the optical system structure based on the secondary imaging of the aperture is also proposed.According to the above proposed methods,the design work of two infrared secondary imaging optical systems in the medium wave infrared target detection device is completed.The F numbers of the two systems are both 2,the field angle is 10°×8° and 5°×4°,100% cold aperture efficiency is reached,in the temperature range of-30?~70?,the MTF values of two systems in the respective Nyquist frequency are greater than 0.6,which achieves an excellent athermal performance.The narcissus of the refrigeration infrared imaging system can cause the degradation of the imaging performance of the system.In this paper,the quantitative evaluation and suppression method of narcissus are studied.Narcissus induced temperature difference(NITD)is used as the quantitative evaluation standard for narcissus,and the quantitative evaluation of narcissus of the infrared imaging system is achieved by the non-sequential ray tracing method.A specific narcissus suppression method is proposed,and the suppression of narcissus of the infrared imaging system is realized by this method.The results show that,when the narcissus is suppressed,the axial NITD of the medium wave infrared 1 imaging system decreases from 0.863 K to 0.114 K at the highest operating temperature,and the difference of NITD between the maximum temperature and the reference temperature decreases from 0.751 K to 0.096K;the axial NITD of the medium wave infrared 2 imaging system decreases from 1.894 K to 0.121 K at the highest operating temperature,and the difference of NITD between the maximum temperature and the reference temperature decreases from 1.394 K to 0.089 K.In addition,the MTF values of the two sets of infrared imaging systems are still greater than 0.6.In order to realize the high precision testing of the MTF of infrared imaging system,an modified slant edge method is proposed in this paper.Given that the edge angle extraction and the ESF construction are susceptible to noise in the traditional method,the edge angle extraction accuracy is improved by the combination of the gradient operator and the regional intercept,and the projection equation of the pixel in the slant edge image is given,through the multiple de-noising method to improve the ESF construction accuracy.The detailed design process of the simulation experiment is given,and the validity of the modified method is proved by the simulation experiment.The influence of the edge angle and the noise on the MTF testing accuracy of the modified method is also analyzed.The simulation results show that the modified MTF testing accuracy is 0.0052 and the testing repeatability is 0.0036,which are superior to the traditional method.In addition,the modified method has strong roughness against noise,and is not affected by the slant edge change.In this paper,the modified slant edge method is applied to the work of fixing focus of the actual infrared imaging system,and the non-uniformity of the infrared imaging system is corrected by using the two point correction method.Based on the MTF test of the actual infrared imaging system,the accuracy of the modified slant edge method is verified,and the correctness of the fixing focus method is also proved.The temperature experiment of the infrared imaging system is operated to verify the athermal performance and the suppression of narcissus,and the validity of the proposed methods are proposed.Finally,the MRTD and distortion of the actual infrared imaging system are tested.