## 3 Datasets  
The polarimetric contrast enhancement method is evaluated with images acquired by different polarimetric SAR sensors over the ocean, with the presence of multiple ships with variable dimensions. The list of images, including relevant details for each sensor, is shown in Table 1.  
We first processed an L-band quad-pol image acquired by ALOS-1 (Advanced Land Observation Satellite) over Tokyo Bay (Japan). We also processed a quad-pol image acquired at the C-band by Radarsat-2 covering the city and the coast of Barcelona (Spain). Additionally, we used dual-pol images gathered by the PAZ SAR satellite in the X-band near the coast of Rio Grande (Brazil). To specifically evaluate the performance of the contrast enhancement method on dual-pol data at the X-band, we processed three PAZ images acquired over the same region with different polarization combinations and on different dates. For additional insights with dual-pol data, we manually selected two channels (from the four available) from the quad-pol images of ALOS-1 and Radarsat-2, enabling further comparison of dual-pol modes at other frequency bands. Additionally, we present an example of polarimetric optimization applied to a dual-pol Sentinel-1 image acquired over the Strait of Gibraltar. Although Sentinel-1 operates at the C-band, like Radarsat-2, its freely available and globally accessible data deserve special consideration, as the satellite is widely used for maritime surveillance. Moreover, since access to commercial satellite imagery is generally more restricted for scientific purposes, including an example based on a free dataset could facilitate further research in this field. This diversity in terms of sensors, frequency bands, and polarizations allows for a rich and complete analysis of the contrast enhancement method. All images were acquired with mid-to-low (i.e., steep) incidence angles (ranging between 25\({}^{\circ}\) and 33\({}^{\circ}\); see Table 1). Therefore, the backscattered signals coming from the sea surface are expected to be considerably high, and the benefits of the contrast enhancement can be better evaluated. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensor** & **ALOS-1** & **Radarsat-2** & **PAZ** & **Sentinel-1** \\ \hline Frequency Band & L & C & X & C \\ \hline \multirow{2}{*}{Polarization} & Quad: & Quad: & Dual: & Dual: \\  & HH, HV, VH, VV & HH, HV, VH, VV & HH, VV; HH, VH; VH, VV & VV, VH \\ \hline \multirow{2}{*}{Acquisition Date} & \multirow{2}{*}{2008\(-\)10-09} & \multirow{2}{*}{2011-04-21} & \multirow{2}{*}{2024-12-12,} & \multirow{2}{*}{2018-01-04} \\  & & & & 2024-12-23 & \\ \hline Incidence angle & 25\({}^{\circ}\) & 28\({}^{\circ}\) & 27\({}^{\circ}\) & 33\({}^{\circ}\) \\ \hline \multicolumn{4}{c}{Pixel Spacing} \\ \multicolumn{4}{c}{range \(\times\) azimuth [m]} & \multirow{2}{*}{\(9.37\times 3.59\)} & \multirow{2}{*}{\(4.70\times 5.10\)} & \multirow{2}{*}{\(1.44\times 2.99\)} & \multirow{2}{*}{\(2.3\times 17.4\)} \\ \end{tabular}
\end{table} 
Table 1: Characteristics of the polarimetric images used in this study. All channels of the SLC images were radiometrically calibrated to the backscattering coefficient (\(\sigma_{0}\)). Then, as the starting point of the contrast enhancement for both the quad- and dual-pol cases, the covariance matrix was generated from the calibrated SLC images. In all cases, the polarimetric covariance matrices were estimated using a 3 \(\times\) 3 boxcar filter (moving average). Note that a small filtering window was used to reduce speckle without significantly degrading the original spatial resolution of the data, as excessive smoothing could hamper the detection of ships (especially small ones). Figure 1 shows a false colour composite of each processed image, which corresponds to specific Regions of Interest (RoIs) within the full scenes. As can be seen in the RGB images, all ships exhibit specific polarimetric responses compared to their surrounding sea areas.