# Ship Detection from X-Band SAR Images Using M2 Det Deep Learning Model
## 2 Study Data  
In this study, images captured by TerraSAR-X and COSMO-SkyMed (Constellation of Small Satellites for Mediterranean basin Observation) satellites were used to detect ships. TerraSAR-X is a German satellite that was successfully launched on June 15, 2007 and is a high-resolution SAR satellite using X-band microwaves. Three modes, namely, the Spotlight, ScanSAR, and StripMap, are supported. Because each mode has different observation widths and resolutions, a mode can be selected according to the purpose of the study. The Spotlight mode provides a 1 m resolution image for a 10 km observation width, and the StripMap mode provides a 3 m resolution image for a 30 km observation width. Finally, the ScanSAR mode provides a 16 m resolution image for a wide viewing width of 100 km. COSMO-SkyMed is a group of four satellites owned by Italy. Similar to TerraSAR-X, they support three modes: the Spotlight mode, ScanSAR mode, and StripMap mode. Among the three modes, the StripMap mode, which provides a 3 m resolution image, was used in this study. Therefore, most ships can be detected considerably well, except very small ships, and thus this mode is suitable for this study. Table 1 lists the details of the TerraSAR-X and COSMO-SkyMed SAR images used in this study. The parameters of each SAR image represent the average value of the images used. The pixel resolution in the flight direction of the TerraSAR-X image is approximately 2.4 m, and the pixel size in the observation direction is approximately 1.9 m. Furthermore, the COSMO-SkyMed image has approximately 2.1 m pixel resolution in both the flight direction and the observation direction. For polarization, both SAR images used the HH mode. In the co-polarization mode, HH polarization is known to have a higher contrast between sea and ship than VV polarization. Therefore, it was expected that this would yield a better ship detection performance [24]. TerraSAR-X used a total of four images, and these images were captured in Songdo, Korea, and the Kerch Strait between the Black Sea and the Azov Sea. COSMO-SkyMed used a total of 26 images, and those images were in Songdo, Korea, and Gyeongju, Korea.  
Figure 1 shows some of the SAR images used in this study. Figure 1e is an enlarged image of a part of an oil spill area in the Kerch Strait in November 2007. Mostly small ships are observed, and the sea surface on which the oil floats is calm. Figure 1f shows a small ship and a large ship together and a calm water surface. In Figure 1g,h, waves are swaying on the water surface, and small ships are observed. As shown in Figure 1, although the contrast between the values of the ship and the sea surface is large in both cases, the conditions of the sea surface and the size of the ship are different in each sea. Therefore, it is important to successfully detect large and small ships that exist at sea surface in various states.  
\begin{table}
\begin{tabular}{c c c} \hline  & **TerraSAR-X** & **COSMO-SkyMed** \\ \hline Mode & StripMap & StripMap \\ Polarization & HH & HH \\ Incidence angle (\({}^{\circ}\)) & 30.03 & 38.07 \\ Azimuth pixel spacing (m) & 2.43 & 2.08 \\ Ground range pixel spacing (m) & 1.89 & 2.12 \\ Number of images & 4 & 26 \\ \hline \end{tabular}
\end{table}
Table 1: Details of COSMO-SkyMed and TerraSAR-X images used in this study. SAR: synthetic aperture radar.  
Figure 1: Intensity image of SAR image used in this study. (**a**) Kerch Strait captured by TerraSAR-X; (**b**) Songdo captured by TerraSAR-X; (**c**) Songdo captured by COSMO-SkyMed; (**d**) Gyeongju captured by COSMO-SkyMed; (**e**–**h**) zoomed in images of the red box region in (**a**–**d**).