Quantitative assessment of speckle filters for SAR images

SAR (Synthetic Aperture Radar) and the related techniques for application have experienced great development. And much attention has been paid to speckle, which results from the coherent imaging process. Because speckle acts as a noise multiplying the underlying RCS (Radar Cross-Section), and it greatly degrades interpretation, identification and other quantitative application of SAR images. Diversified speckle reduction techniques have been proposed to reconstruct the underlying RCS from the observed SAR image. So the need for assessment criteria of speckle filters becomes pressing. Based on study of properties of SAR imagery and the existent filters, evaluation criteria of speckle filters are analyzed, and quantitative indexes can be adopted in practical application are proposed according to the criteria. Radiometric and spatial indexes for quality of SAR images are applied to speckle reduction in uniform areas and isolated scatterer preservation. Reasonable indexes are defined for edge preservation and radiometric distortion, respectively. Simulated and real SAR images are used for experiment. The experimental results accord with theoretical analysis of the testing filters. This agreement demonstrates the effectiveness of the proposed indexes. Distribution of speckle image suggests another way for evaluation, but further study is needed to bring it to practical application by χ² goodness-fit-test.