强辐射环境下CMOS图像传感器噪声对相机分辨率的影响

CMOS图像传感器（CIS, CMOS image sensor）相机是照相装置中常用的成像设备。在核工业环境下的监控过程中，CIS易受γ辐射影响产生噪声，影响图像的成像分辨率，有必要从系统角度评估CIS相机抗辐照能力。通过利用60Co?γ放射源对CIS相机进行辐照实验，分别得到了典型CIS相机的噪声与图像分辨率和辐射剂量的函数关系，进而求出满足相应分辨率条件下CIS相机的辐照剂量上限。研究结果显示，对于相机成像图片目标区域的最小灰度值区域噪声数量占比σ≤2%，CIS相机电离总剂量（total ionizing dose, TID）小于150 krad（Si），相机分辨率没有明显降低。并且在通过ISO 12233: 2014 eSFR测试相机分辨率中发现，利用基于楔形图获取混淆的开始频率测试法评估辐照相机分辨率参数比SFR测试法更具合理性。

Noise of CIS Effect on Imaging Resolution of Camera under High Radiation Environment

CMOS image sensor (CIS) cameras are common imaging devices, compared with charge coupled device (CCD), CIS has unique advantages such as small size, high integration, low power consumption and lightweight. In the process of monitoring in the nuclear industry environment, the CIS and camera motherboard are vulnerable to noise caused by gamma radiation, which can affect the imaging resolution of the image. Therefore, it is necessary to evaluate the anti?radiation ability of CIS camera from a systematic perspective and analyze different test methods of camera resolution after irradiation. By using 60Co?γ radiation source to irradiate CIS camera, the irradiated CIS camera was combined with irradiated mainboard and unirradiated mainboard to form different cameras, and the two kinds of cameras were tested. The following data can be obtained from camera tests, such as, the relationship between dark current and cumulative dose of CIS after irradiation, the relationship between resolution value and cumulative dose under different test methods based on ISO 12233 standard, the relationship between the number of noise points in the minimum gray value area and the maximum gray value area of the target area of the test card image collected by the camera, the relationship between the average number of noise points in the whole target area and the cumulative dose, and the relationship between the gray value of the resolution test card and the cumulative dose. The functional relationship between noise and modulation transfer function (MTF) of the irradiated imaging system was established through the theoretical derivation of MTF, by putting the gray values of the resolution test card under different cumulative doses into formulas to obtain the functional relationship between the radiation dose of the calculated MTF value. Finally, by analyzing the theoretical calculation and the actual measurement of MTF value, the functional relationship between noise and image resolution and radiation dose of the typical CIS camera was obtained, and then the upper limit of radiation dose of the CIS camera under the corresponding resolution was obtained. The results show that both CIS noise and camera motherboard noise have an impact on camera resolution, and the noise increases with the increase of cumulative dose. The total ionization dose of the camera is less than 150 krad(Si), camera resolution is not decrease significantly. In ISO 12233 eSFR resolution test, it is found that it is more reasonable to evaluate the resolution parameters of the irradiated camera by using aliasing onset based on the wedge pattern test than the SFR test method.