基于月球观测的“高分四号”卫星相机在轨MTF测试

The Lunar Trail of GF-4 Satellite and On-orbit Knife-edge Measurements of MTF

针对"高分四号"(GF-4)卫星在轨调制传递函数(MTF)测试,提出了一种从月球观测试验获得的月球图像中提取刃边目标进行计算的方法。月球表面与宇宙暗背景形成的对比强烈的刃边特征是比较理想的阶跃函数。倾斜刃边法是基于阶跃函数开发的MTF测试方法,在航天光学遥感领域得到了广泛应用。文章对倾斜刃边法进行改进,将月球边缘近似为圆处理,利用一阶梯度算子(Sobel operator)提取圆形刃边,开发适用于圆形刃边的MTF算法。将改进后的算法应用于GF-4卫星对月图像,获取在轨MTF,并与实验室测量结果进行了对比:在B2～B5谱段,测试结果均值与地面测试结果分别相差5.6%、3.7%、11.1%、2.5%。在此基础上,对误差来源、测量结果的差异性进行了分析说明。

In order to calculate the modulation transfer function(MTF)of GF-4 on orbit,an algorithm is developed.Taking the high-contrast images of lunar edge as a target,the curved knife-edges of a lunar image are captured and then applied to estimate the MTF for various bands of GF-4 using the knife-edge method.In this paper,the lunar edge is extracted by a Sobel operator and treated as a full circle.The mean value differences between the fitted and the designed are within 5.6%,3.7%,11.1%,2.5%in the B2,B3,B4 and B5 bands respectively.Finally,the possible error sources of this algorithm are also discussed.