高超声速流场成像质量特性及校正方法

光学成像制导飞行器在大气层中以高超声速飞行时,其成像窗口附近强压缩流场的气动光学效应会导致成像过程出现抖动、偏移和模糊,影响制导精度.为研究该问题,搭建了基于高超声速(Ma=6.0)炮风洞的气动光学地面模拟平台.利用高速摄像机获取了多种喷流压比状态下光学头罩成像图片,研究了成像特性.基于背景纹影技术(background oriented schlieren, BOS)直接获取气动光学畸变的点扩散函数信息,结合Wiener滤波方法对地面模拟平台获取的成像畸变结果进行了校正,并结合灰度分布、峰值信噪比(peak signal-to-noise ratio, PSNR)和结构相似度(structural similarity, SSIM)对校正结果进行了定性和定量评价.成像结果表明,头罩无冷却喷流时成像质量最好,在压力匹配附近头罩成像质量相对于欠压喷流和过压喷流成像质量较好.图像校正结果表明,风洞运行过程中采集的时间序列图像在校正之后所对应的灰度分布情况、PSNR和SSIM都得到提高.

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.