基于面阵CCD的时间延时积分模式的空间相机自动对焦

Method to Realize Autofocus of Remote Sensing Camera Based on the TDI Pattern of Interline Transfer Progressive Scan CCD

空间面阵相机在轨运动会产生运动模糊,影响自动对焦准确率。为解决该问题,提出行间转移面阵CCD的时间延时积分(TDI)模式实现去运动模糊。选取行间转移面阵CCD KAI-1003作为成像器件,利用可编程逻辑器件(PLD)控制时序信号,匹配CCD的行转移速度与目标运动速度,实现去运动模糊。实验表明该成像系统不仅能去运动模糊而且还大幅提高图像信噪比。去运动模糊后,根据较短时间间隔内空间相机拍摄的图像有重叠区域的特点提出一种空间相机自动对焦方法。通过配准算法找出序列图像间的重叠区域,并计算重叠区域的清晰度评价值,然后根据传递特性将评价值映射到同一个评价体系中,最后找到最佳对焦位置。实验表明该成像系统对高速运动的目标能够实现自动对焦。

The picture captured by the remote sensing camera will be degenerated since the camera constantly rotates around the earth. The degenerated image may decrease the focusing accuracy. In order to solve this problem, a method based on the time delay and integration （TDI） pattern of interline transfer progressive scan CCD is proposed. The interline transfer CCD KAI-1003 is used as the imaging device, and PLD is used to control the driving timing signal for the sake of matching the velocity between CCD and object. In this way, the motion blur can be eliminated. The experimental results show that the imaging system not only eliminates the motion blur but also increases the signal to noise ratio （SNR） of the image. Mter removing the motion blur, an auto-focusing method of remote sensing camera is also proposed, with the feature that the images have overlapped regions captured in a short time. Firstly, the displacement and the overlapped regions of two adjacent images in the image sequences are calculated using the image registration algorithm. Then a sequence of focusing accuracy values through performing a sharpness evaluation function on the overlapped region of each image is obtained. Finally, according to the transfer characteristic, the evaluation value is mapped in a same evaluation system, and the accurate focus position is found. The experimental results indicate that the imaging system works pretty well for auto-focusing when the object moves in a high speed.