## 4 Results
### Results with Quad-Polarimetric Data
(or dispersed) across a wider area, as shown in the magnified region of Figure 4. In the optimum image represented in Figure 4c, we observe a clear cancellation of the signal coming from the sea surface, as well as an improved contrast between each vessel and its surrounding area. Figure 5 shows an azimuth (vertical) transect through the leftmost ship that appears in Figure 4 (highlighted with the red circle). Here, we observe that the HH polarization exhibits higher backscatter values for both the sea and the vessel (as previously stated), with an intensity difference of around 15 dB between the ship and the sea, as represented with the blue plot of Figure 5. Backscattered signals from the sea surface are notably reduced in the HV polarization, with an intensity difference of approximately 30 dB between the target vessel and its background (green plot). The signal-to-clutter ratio is clearly enhanced in the optimum channel, as illustrated by the red plot in Figure 5. The peak corresponding to the ship pixels is similar to that of HH and HV channels, but the average intensity level of the sea area is lower than that observed in the HV channel (around \(-\)35 dB), which indicates that it provides the highest contrast. As a further observation, examining the transects in Figures 3 and 5, we notice significant fluctuations in very low intensity values in the optimum channel (ranging from \(-\)35 to \(-\)50 dB). These fluctuations are certainly caused by the presence of speckle in the estimation of the covariance matrices. It is important to note that a small filtering window of 3 \(\times\) 3 pixels was used during estimation to minimize the loss of image resolution, resulting in a low equivalent number of looks. This leads to an inhomogeneous cancellation of sea clutter across all image pixels by means of the optimization process. Nonetheless, it is evident that sea clutter is consistently reduced compared to the original channels, and a similar effect will be observed when processing dual-polarization data. Table 3 presents an estimation of the signal-to-clutter ratio for the same ship. Similar to the previous example with L-band data, the optimized image achieves a higher signal-to-clutter ratio. However, the improvement in this case is less pronounced, with an increase of +6 dB compared to +23 dB in the previous example. In any case, the enhanced contrast between the ship and the sea clutter would improve the automatic detection capabilities of any algorithm. Figure 3: Range transects through ship shown in magnified region in upper part of Figure 2, corresponding to L-band quad-pol ALOS-1 image over Bay of Tokyo. Figure 4: Optimization results of the C-band quad-polarimetric image acquired over Barcelona (Spain) by Radarsat-2. All figures represent the image intensity in logarithmic scale ranging from \(-35\) to \(0\) dB. The red circle is used to indicate the ship used to visualize the transects of Figure 5. Yellow circles highlight the rest of vessels present in the scene. Figure 5: Azimuth transects through ship shown in magnified region in upper part of Figure 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Polarization** & **HH** & **HV** & **Optimum** \\ \hline Signal-to-Clutter & & & \\ Ratio [dB] & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Signal-to-clutter ratio between the ship highlighted with the red circle in Figure 4 and its surrounding sea clutter for different polarimetric channels.