Speckle in synthetic aperture radar （SAR） images disturbs SAR images calibration

validation

and interpretation. Thus in most cases of practical interest

reducing speckle in SAR images is a goal towards which we aspire. Over the past 20 years

numerous methods to reduce speckle have been proposed based on digital image processing after the images have been formed. A number of filters have been proposed to reduce speckle based on speckle models

such as the Lee

the Kuan

the Frost

the modified Lee

modified Frost

and filters based on the Maximum A Posteriori （MAP） probability. Meanwhile other filters are not based on speckle models

such as median filter

geometric filter

and wavelet transform filter but also have been applied to reduce speckles. The primary goal of these methods is to reduce speckle without destroying resolution and edge information. In fact

the experiments indicate that there is always a kind of tradeoff between smoothing out speckle and preserving the useful information. It is an inverse problem to restore images with speckle on mathematical physics view. The common attribute of inverse problem is ill-conditioned. Thus

it is impossible to obtain the true image from the images with speckle. Even so

approximate image can be restored from images with speckle on certain condition. In fact

many methods to restore image with speckle have been proposed based on different principle. The different images can be acquired from the same image with speckle using different filters. This makes a problem that which image is optimal. In the general

an optimal filter is well-balanced in the quality of visual appearance

mean preservation

edge preservation

and reduction of the standard deviation. In this paper

an enhanced SAR speckle filter is developed. It can effectively smooth out speckle while preserve edge information.