## 3 The Proposed Method
### Polarimetric Parameters Extraction
The histograms of the double-bounce powers of the normal water region and the interference water region are shown in Figure 4c,d, respectively, where the red lines stand for the distribution fitting result. Comparing Figure 4c,d, we can find that the minimum power of the interference water is far larger than the maximum power of the normal water. Thus, the interference water is easy to separate from the normal water using the double-bounce power. Figure 4: The histograms of the double-bounce and the volume scattering powers of different sampled water and land regions where the distributions are fitting using a gamma distribution shown with a red line: (**a**) The histograms of normalized power \(P_{s}/\)Span, \(P_{d}/\)Span, and \(P_{o}/\)Span of the port water; (**b**) the scattering distribution of \(P_{s}/\)Span, \(P_{d}/\)Span, and \(P_{o}/\)Span components of the sampled water and land regions; (**c**) the double-bounce power of a normal water area; (**d**) the double-bounce power of an interference water area; (**e**) the volume power of an interference water area; (**f**) the volume power of a land area. Although the double-bounce scattering power of the interference water is larger than that of the normal water, the difference in the volume scattering power between the interference water and the normal water is small since the interference component is dominated by double-bounce scattering. The volume scattering powers of both the interference water and normal water are all much lower than those of the land. The histograms of the volume scattering power of the interference water region and the land region are shown in Figure 4e,f, respectively. Comparing Figure 4e,f, we can observe that the minimum power of the vegetation region is far larger than the maximum power of the interference water. Thus, the water region can be separated from the land using the volume scattering power. By a combination of the double-bounce power \(P_{d}\) and the volume power \(P_{v}\), the interference water in the ports can be extracted from the image. However, a negative power problem exists in the Freeman decomposition. We can observe that the double-bounce powers of half of the sampled normal water pixels are negative from Figure 4c. To avoid the problem, we can obtain the double-bounce scattering power \(P^{\prime}_{d}\) and volume scattering power \(P^{\prime}_{v}\) using (6). The scattering distributions of the \(P^{\prime}_{d}\) and \(P^{\prime}_{v}\) of the sampled water and land regions are shown in Figure 5a. We can observe that the water regions and the land are separable using \(P^{\prime}_{v}\), and the interference water and calm water are separable using \(P^{\prime}_{d}\). However, the difference of \(P^{\prime}_{d}\) between the interference water and calm water is small. Except for the interference water regions, there are some land regions also interfered with by the surrounding man-made buildings or strong scatterers. If an interference land region is soil or another low scattering region, its volume scattering power is so low that it is segmented to a water region by the thresholding segmentation of \(P^{\prime}_{v}\). Since the average difference of the double-bounce scattering power between the interference land region and the interference water is small, it is difficult to identify the two regions using \(P^{\prime}_{d}\). To avoid a false result and enhance the contrast of \(P^{\prime}_{d}\) between the interference water and the interference land region, the PRDV parameter is proposed to separate the interference water and the normal water. The parameter is defined as follows:  
\[PRDV=\frac{P^{\prime}_{d}}{P^{\prime}_{v}}, \tag{7}\]  
where \(P^{\prime}_{d}\) denotes the double-bounce scattering power, and \(P^{\prime}_{v}\) denotes the volume scattering power. Because the volume scattering power of the interference water region is lower than that of the interference land region, the PRDV parameter of the two kinds of regions is separable. Let PV denote \(P^{\prime}_{v}\).