Then, a new two-step filtering method has been extracted according to the f eature of reference image.The first step one is homomorphic filtering and the s econd step is minimum variance filtering.

• 然后根据基准图的特点提出了用同态滤波及最小方差滤波的两步法对基准图进行滤波，这一方法特别适用于因薄云覆盖而引入的低频噪声的处理，并同时兼顾了图像的增强与恢复。