高超声速激波辐射对红外成像系统的影响分析

带有红外成像探测系统的飞行器在大气层内高速飞行时,其光学窗口外高温激波流场的热辐射将降低成像探测的信噪比和探测距离。先根据近场辐射成像光路的几何关系推导了焦平面上单元像素接收的流场辐射功率和流场向其与窗口界面外发射的辐射亮度的函数关系,然后采用箱带模型描述流场的辐射机制,再求解辐射传递方程以计算该辐射亮度。计算了探测器上的流场辐射功率分布和目标的辐射成像结果。计算结果表明:激波流场为光学薄介质,其对目标辐射的吸收可以忽略;成像系统接收的流场辐射能量为非均匀背景噪声;当高度不变、马赫数增大时,该能量将增大,所以信噪比将减小;当马赫数不变、高度增大时,该能量将减小,所以信噪比将增大。

Analysis of hypersonic shock layer radiance effect on an IR imaging system

When an endo-atmospheric vehicle carrying an IR imaging detection system flies at a high speed,radiance of shock layer near its IR window degrades SNR and detection range of the system.Firstly,based on the geometric relation of the near field radiance imaging,the relation between shock layer radiance power received by every pixel in the focal plane and radiance emitted by the shock layer outside the boundary between the shock layer and the window was deduced.Secondly,the box model was selected to describe gas radiation characteristics in the shock layer.Thirdly,the radiative transfer function was solved to calculate the radiance.Shock layer radiance power received by every pixel of the detector array and the imaging result of a target were calculated.The results show that the shock layer is optically thin medium,so the target radiance absorbed by it can be neglectable.The calculation results show that the shock layer radiance power received by the imaging system is inhomogeneous background noise.To a certain altitude,when Mach number increases,the power increases,so the SNR decreases;and to a certain Mach number,when altitude increases,the power decreases,so the SNR increases.