GF-2星全色相机在轨MTF测量和图像复原研究

On-orbit MTF estimation and restoration of GF-2 satellite image

调制传递函数(modulation transfer function,MTF)不仅是监测遥感卫星光学相机在轨运行情况和性能的有效手段,也是对卫星图像进行复原处理的重要参数。利用刀刃法对高分二号(GF-2)卫星全色相机进行MTF在轨测量。在计算MTF的过程中,使用汉明窗对截取后的线扩展函数(line spread function,LSF)曲线进行处理,以抑制截取过程所造成的频谱泄露。此外,还对截取后LSF曲线的两端补0,扩展LSF曲线的长度,以提高傅里叶变换时的采样频率。实验结果表明,使用本文刀刃法计算所得的MTF采样密度比传统方法提高了5倍,使得MTF曲线更为平滑,提高了MTF的数值精度,有利于后续的图像复原处理。基于传统刀刃法和本文刀刃法计算所得的MTF测量结果,采用维纳滤波法分别对GF-2全色图像进行复原处理研究。结果表明,对2种方法得到的MTF测量结果的维纳滤波均可明显提高图像的清晰度和边缘细节信息;但使用本文方法得到的MTF结果可使复原后的图像在对比度、边缘能量和平均梯度等关键指标上均优于使用传统方法得到的MTF结果。

Modulation transfer function（MTF） is not only an efficient method for monitoring the on -orbit satellite operation status and performance but also an important parameter which is often used to restore satellite image. In this paper, the knife edge method was used to measure the on - orbit MTF of GF - 2 satellite panchromatic camera. During the calculation of MTF, Hamming window was used in the process of clipping the line spread function （LSF） in order to restrain the leak of frequency spectrum. Besides, the authors expanded the LSF with zeros so as to improve the sampling frequency during the Fourier transform. The experimental results show that the sampling density of MTF using the knife edge method proposed in this paper is 5 times more than that of the traditional method and the MTF curve is also smoother compared with that of the traditional method. Therefore, the more accurate MTF matrix value can be obtained to improve the performance of image restoration by this method. In this paper, the Wiener filtering method was used to restore the GF - 2 satellite panchromatic image with the MTF matrix value. The experimental results also show that the MTF matrices computed by the two methods can all improve the clearness and object edge information of the image. However, the image restored by the MTF matrix values of the authors＇ method is superior to that of the traditional method in such characteristics as contrast, edge energy and average gradient.