天问一号高分相机CMOS曝光参数设计与卷帘校正

CMOS exposure parameter design and rolling shutter distortion correction for Tianwen-1 high-resolution camera

为获取高信噪比、明暗度适宜的火表图像,对天问一号火星高分相机CMOS探测器曝光参数开展了详细设计,并对卷帘效应畸变进行了量化分析与校正。首先建立了CMOS探测器光电响应模型,对比了曝光参数中曝光时间与PGA增益对成像信噪比的影响,确定曝光时间为优先调节参量。在分析曝光时间约束条件、明确靶面辐照度计算方法后,给出了不同火表反射率、太阳天顶角及轨道高度参数下的曝光时间设计结果与成像信噪比。最后针对CMOS探测器卷帘畸变机理进行分析,给出了校正方法及理论校正精度。仿真实验结果表明:成像信噪比在非轨道像移受限区域保持在48.28 dB左右,在受限区域则逐步降低,反射率取0.1时最低值为32.45 dB,典型辐照环境下成像信噪比为45.56 dB。根据实际轨道像移分析,CMOS探测器卷帘效应会造成数十像素倾斜畸变,在轨道像移测量误差不超过3.46‰前提下,所述方法校正后图像特征点位移量优于1个像素。

To obtain an image of the Martian surface with a high signal-to-noise ratio(SNR)and suitable brightness,the exposure parameters of the CMOS detector in the Mars high-resolution camera were designed,and the rolling shutter distortion was analyzed and corrected quantitatively. First,the photoelectric response model of the CMOS detector was established. By comparing the influence of exposure time and PGA gain on SNR,the exposure time was determined as the priority adjustment parameter. After analyzing the constraints of exposure time and clarifying the calculation method of target irradiance,the exposure time design results and SNR under different reflectivities,solar zenith angle,and orbit height parameters were given. Finally,the distortion mechanism of the rolling shutter was analyzed,and the correction method and theoretical correction accuracy were presented. The simulation results indicate that the SNR remains at approximately 48. 28 dB in the non-orbital image-motion restricted area,and gradually decreases in the restricted area,with a minimum value of 32. 45 dB when the reflectivity is 0. 1. The SNR is45. 56 dB in a typical irradiation environment. Under the orbital parameters,the rolling shutter of the CMOS detector causes tens of pixels of tilt distortion. Under the premise that the image motion measurement error does not exceed 3. 46‰,the image displacement after correction using the proposed method is better than 1 pixel.