海洋SAR图像小波Speckle滤波及边缘信息提取

Using Wavelet for Filtering Speckle and Exacting Edge from Ocean SAR Image

以海洋SAR图像的speckle滤波和边缘信息提取为研究目标 ,构造了以低通带通窄和时域冲击响应系数分布呈左右对称为特征的小波滤波器。这些特征使该小波滤波器在处理突变信号方面具有优良的特性。应用该小波滤波器 ,采用Wiener滤波算法 ,对海洋SAR图像进行了speckle滤波及采用Prewitt算子对边缘信息进行提取。用几种经典小波基函数采用相同的滤波算法和边缘增强算子进行了处理 ,并将它们的结果进行了对比分析。结果表明 ,虽然小波基函数在用于speckle滤波方面 ,稍逊其它几种经典小波基函数 ,但是在边缘信息保留方面 ,效果要明显优于其他小波基函数。

Due to the fact that SAR generates images by coherently processing the scattered signals, the images are highly susceptible to speckle effects, and the intensity of speckle noise obeys a negative exponential distribution and is a multiplicative noise. This phenomenon seems special more obvious on the ocean SAR images than the others. According to the feature of the speckle of ocean SAR image, a new mother wavelet function was constructed. It possesses narrow band in the low_pass and symmetry distribution of impulsion response coefficient in time region, enabling it has an excellent performance in dealing with wave signal aspect. For an original ocean SAR image with size of 1024 by 1024, the Wiener filter algorithm was adopted and the new wavelet filter was applied in order to firstly suppress speckle and then to extract the edge information with Prewitt filter algorithm. Compared several classic mother wavelet functions with the new wavelet function using the same processing method and uniform image, the result shows that the new mother wavelet function is much better than other compared mother wavelet functions in preserving the image's edge information, though its performance is not good enough in suppressing speckle. Based on the above discussion, it is obvious that the wavelet filter is a very effective method in speckle filtering and the new constructed mother wavelet function plays an important role in extracting SAR image edge feature.