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摘要: 本文研究了卷帘快门式CMOS成像器件在拍摄星图时引入的快门效应。根据卷帘快门CMOS图像传感器的成像原理和特点, 分析了星图中由于快门效应导致的星点变化情况，对该成像方式引入的图像变形，提出了一种像移补偿方法。该方法在已知星图拍摄帧频、CMOS图形传感器相邻行曝光时间间隔的基础上，通过对相邻星图中的星点进行目标提取、质心计算以及星点质心匹配等操作，完成景物在像面上像移速度的计算，最后结合该速度值和CMOS图像传感器的行曝光时间间隔，计算星点质心在单帧星图中的像移，逆向补偿。通过实际拍摄的星图对算法的效果进行测试，实验结果表明，利用补偿后的星图解算姿态数据时，其中非机动模式下与两个星敏的夹角误差可达到0.5″以内，机动模式下与两个星敏的夹角误差也可达到0.6″左右，不仅明显优于补偿前，且精度高于很多目前主流的星敏感器。该实验结果不仅证明了算法的有效性，而且在一定程度上推广了卷帘快门式CMOS 相机在航空航天领域的应用。Abstract: According to the imaging principles and characteristics of a shutter CMOS image sensor, the shutter effect introduced by a shutter CMOS image detector operating on a star map is analyzed, and an image shift compensation method is proposed to rectify the image distortion introduced by this kind of imaging method. With the known frame frequency of the star images and the exposure time interval of the adjacent rows of the CMOS graphic sensor, this method can achieve high-speed calculation of star motion by extracting and matching the centroid of the star points in an adjacent star map. The centroid of the star points in a global image is calculated by combining the speed value with the row exposure time interval of the CMOS image sensor. The effect of the algorithm is tested on actual star images. The experimental results show that with the compensated star map, angle errors between the star sensors are smaller than 0.5″ when a satellite is in non-maneuver mode, and angle errors between either of the star sensors are about 0.6″ when the satellite is in maneuver mode. The experimental results not only prove the effectiveness of the algorithm, but also broaden the applications of shutter CMOS detectors to some extent, especially in aerospace engineering.
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Key words:
- CMOS image sensor /
- rolling shutter /
- star map /
- star extraction /
- star point matching
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图 6 相邻两帧图像的星点提取结果对比
Figure 6. Comparison of star extraction results between two adjacent star images
表 1 非机动模式下星相机光轴与a星敏之间的夹角误差
Table 1. Angle error between the star-camera and star sensor a in non-maneuver mode
序号 俯仰角/° 侧摆角/° 补偿前误差1σ/″ 补偿后误差1σ/″ 1 0.549 −6.516 4.353 0.540 2 0.051 −36.699 5.424 0.439 3 0.152 −16.769 7.147 0.768 4 0.334 12.903 6.284 0.702 5 0 −5.542 4.177 0.377 6 0 8.672 4.491 0.384 7 0 12.284 5.261 0.546 8 −0.231 10.533 5.535 0.231 9 −0.370 −24.558 4.225 0.300 10 3.023 −25.764 5.360 0.481 平均值 5.249 0.476 
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表 2 非机动模式下星相机光轴与b星敏之间的夹角误差
Table 2. Angle error between the star-camera and star sensor b in non-maneuver mode
序号 俯仰角/° 侧摆角/° 补偿前误差1σ/″ 补偿后误差1σ/″ 1 0.549 −6.516 5.607 0.420 2 0.051 −36.699 5.186 0.317 3 0.152 −16.769 4.375 0.211 4 0.334 12.903 3.876 0.361 5 0 −5.542 3.968 0.249 6 0 8.672 3.233 0.297 7 0 12.284 5.261 0.567 8 −0.231 10.533 2.984 0.185 9 −0.370 −24.558 3.889 0.266 10 3.023 −25.764 3.960 0.202 平均值 4.234 0.308
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表 3 机动模式下星相机光轴与a星敏之间的夹角误差
Table 3. Angle error between the star-camera and the star sensor a in maneuver mode
序号 俯仰角/(°) 侧摆角/(°) 补偿前误差1σ/″ 补偿后误差1σ/″ 1 0 −18.191 7.754 0.818 2 0 −31.961 6.686 0.532 3 0 2.597 5.914 0.318 4 0 5.154 7.387 0.714 5 0 3.855 7.996 0.734 平均值 7.147 0.623
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表 4 机动模式下星相机光轴与b星敏之间夹角误差
Table 4. Angle error between the star-camera and star sensor b in maneuver mode
序号 俯仰角/° 侧摆角/° 补偿前误差1σ/″ 补偿后误差1σ/″ 1 0 −18.191 8.134 0.543 2 0 −31.961 6.563 0.392 3 0 2.597 4.782 0.241 4 0 5.154 5.973 0.616 5 0 3.855 6.189 0.932 平均值 6.328 0.545
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