Hypersonic Flow Field Imaging Quality Characteristics and its Correction Method

When an optical imaging guided vehicle flies at a hypersonic speed in the atmosphere, the aero-optical effects of the strongly compressed flow field near the imaging window can cause jitter, offset, and blurring in the imaging process, affecting the guidance accuracy. In order to address this problem, a pneumatic optical ground simulation platform based on hypersonic (Ma = 6.0) gun tunnel was built. The imaging result of optical hoods under various jet-pressure ratio conditions was obtained by high-speed camera. The imaging characteristics were investigated, as well. After that, the point spread function of the aero-optical distortion was directly obtained based on the background oriented schlieren (BOS) technique, and the imaging distortion result obtained by the ground simulation platform was corrected by the Wiener filtering method. The gray distribution, the peak signal-to-noise ratio (PSNR) and structural similarity index measurement(SSIM) were used to qualitatively and quantitatively evaluate the calibration results. The imaging results show that the image quality of the hood is the best when there is no cooling jet, and the image quality of the hood near the pressure matching is better than that of the underpressure jet and overpressure jet. The image correction results show that the gray-scale distribution, PSNR and SSIM of the time series images obtained during the operation of the wind tunnel are improved after correction.