CBERS-02B卫星WFI成像在轨MTF估算与图像MTF补偿

基于高分辨率图像对比法, 利用同一卫星平台上空间分辨率19.5m的CCD相机图像对CBERS-02B卫星上空间分辨率为258m的 WFI成像仪图像进行在轨MTF(modulate transfer function)测量, 获得WFI(wide field imager)相机沿轨、跨轨与45o方向的MTF曲线, 并计算出3个方向的线扩展函数LSF(line spread function), 获得3个方向的有效半带宽。结果表明WFI相机红波段跨轨、沿轨与45o方向的有效半带宽, 即有效瞬时视场, 分别为1.188, 1.165与1.281个像元, 近红外波段为1.258, 1.195与1.326个像元。基于获得的MTF, 利用维纳滤波法对WFI图像进行补偿, 部分恢复了WFI图像的细部信息。

Image-derived MTF method and MTF compensation for CBERS-02B WFI imager

In this paper, a method to evaluate the in-flight MTF (Modulate Transfer Function) of the WFI (Wide Field Imager) on CBERS-02B is presented and the WFI images are restored. The CCD is another payload on CBERS-02B with high spatial resolution. Using the CCD images as high resolution images, the two-image comparison approach is applied to determine the MTF of the WFI with a pair of images acquired over Beijing on Nov. 10, 2007. As the results, MTF values in three directions are derived. The MTF values at Nyquist frequency in cross-track, in-track and 45° directions were respectively about 0.43, 0.52 and 0.35 for red band and 0.30, 0.46 and 0.36 for near-infrared band. Image-derived MTF values are applied to calculate the half bandwidths of the WFI. The results indicate that the instant fields of view of the WFI in the cross-track, in-track and 45o-track directions were respectively 1.188 pixels, 1.165 pixels and 1.281 pixels for red band, and respectively 1.258 pixels, 1.195 pixels and 1.326 pixels for near-infrared band. Weiner filter model is used to perform the MTF compensation for WFI images. The results show that the restored image seemed clearer and contained more detailed information.