Using knowledge which has been known beforehand in Grads Range,this paper proposes an image segmentation method which can solve the problem.

Because of the high similarity between the gradient magnitudes of low-contrast edge and noise,the conventional Canny algorithm for detection,which is based on the double-threshold to detect and connect edges,damages partly the low-contrast edge though it suppresses noise.

The image s gradient magnitude mean and the variance of every pixel in the image relative to the gradient magnitude mean are calculated according to the method proposed in the paper.

In order to study the corresponding optimal signal processing algorithm, this paper elemefltarily analyzes its amplitude statistical distribution, power spectrum and time varying spectrum so that we can have better understanding of sea clutters.

A method that combines non-statistic amplitude filtering and statistic phase filtering to improve the coherence of airborne InSAR interferograms is proposed,and a cost function is given to combine the phase unwrapping blocks for a large interferogram.