Experimental Study On Hypersonic Aero-optical Imaging Characteristics Analysis And Its Calibration Method

During the guided flight,the hypersonic imaging guided vehicle has a complex flow field on the imaging optical path,and the compressibility of the flow field and its internal flow structure bring complex density field distribution,which is non-uniform in time and space.The distributed density field can have complex distortion effects on the transmission of light.During the flight,the imaging optical window of the aircraft is also affected by severe aerodynamic heat.The aerodynamic heat can cause the window to ablate and deform and change the optical properties of the window.At the same time,the strong infrared radiation of the aerodynamic heat will also reduce the sensitivity of the detector.The supersonic nozzle is used to generate a gas film to isolate the window from the window external flow,so as to effectively cool the window,thereby effectively controlling the damage of the physical properties of the window by the aerodynamic heat.The step effect behind the nozzle and the intervention of the cooling film introduce more complex changes to the flow field structure on the optical path.The density of the flow field is more difficult to control,which makes the optical imaging quality lower and the imaging law more complicated.The imaging experiment of optical hood under hypersonic conditions was carried out on the high-speed artillery wind tunnel of National University of Defense Technology.Combining cross-correlation algorithm,optical transfer function acquisition algorithm,image quality analysis algorithm and image filtering method,the paper studied the imaging quality characteristics of hypersonic optical hood under different jet pressure ratio(Pressure Ratio of Jet,PRJ)..The high-speed camera is used to collect the background image and combined with the background smear technique(Background-oriented Schlieren,BOS)to obtain the deflection information of the light passing through the hypersonic flow field.On this result,the acquisition method of the flow field geometric optical transfer function is studied.Combined with Wiener filtering,the distortion image was corrected.When the imaging method was analyzed,it was found that the image quality of the optical hood after the introduction of the jet was lower than that of the non-jet flow condition,and the image quality of the matched jet imaging was better compared with other jet conditions.The image correction effects were evaluated from both qualitative and quantitative aspects.The corrected image gray distribution has been significantly improved,and the image PSNR value and SSIM value are significantly improved.