## 3 Materials and Methods
### Class Definitions  
The definition of each DLRI stage used in this research is justified by considering the STANAG 3769 \"minimum resolved object sizes and scales for imagery interpretation\" as a reference [51]. After reinterpreting these definitions according to the purposes of this research and adding a new definition for localization, the DLRI stages can be described as follows:  
* Detection: The discovery of the ship's existence (s) in the optical satellite image. * Localization: Determination of the ship's precise location (s) in the given optical satellite image. * Recognition: Defining the parent class of each image among the civilian and navy ship groups. * Identification: Defining the precise child class of each navy ship. The parent ship classes were initially determined by Lloyd's Register ship classification [52] and Jane's Fighting Ship classification [53]. We re-arranged the classes of VHRShips after analyzing the obtained satellite images and ship representations. According to the class definitions, the VHRShips dataset includes 11,179 ships in 24 parent and 11 child ship categories, which are given in Tables 2 and 3. The parent classes contain one navy and 23 civilian ship class definitions, and stand for the recognition level classification. On the other hand, the child classes detailed 11 navy ship classes of the navy parent class, representing the identification level classification. VHRShips is a diverse and comprehensive dataset aiming to represent various real-life conditions. It includes complex backgrounds such as urban, civilian, navy shores, bridges, breakwaters, forests, canals, small and big islands/cliffs, and industrial zones. The dataset also comprises images with different ocean spectral properties, an advantage of worldwide image selection strategy. Some images contain atmospheric disturbances such as fog, haze, or clouds. Moreover, VHRShips includes some images of rough sea conditions and some images of ship wakes. These properties make it challenging to obtain successful results for all of the DLRI stages. Appendix A Table A1 demonstrates the geographic locations of the collected images used to create this dataset. \begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Value/Description** \\ \hline Number of images & 6312 \\ Number of images with ship(s) & 5312 \\ Number of images without ship & 1000 \\ No. of ships & 11,179 \\ No. of classes & 24 parent, 11 child \\ Image spectral channel & red-green-blue \\ Image spatial resolution & 1280 \(\times\) 720 \\ Image source & Google Earth Professional \\ Bounding box (bBox) type & Horizontal-rectangle \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \multicolumn{2}{c}{} \\ \end{tabular}
\end{table} 
Table 2: VHRShips dataset specifications. After conducting initial experiments, we re-arranged the original dataset to minimize the confusion of some very similar ship classes. After this modification, this research employed the DLRI process with sixteen parent ship classes for the recognition-level classification, and eight child navy classes for the identification-level classification. This specified dataset is generated from the original dataset by performing a re-group process, which is detailed below:  
* dredging and bargePontoon classes are grouped into bargePontoon (representing the steady platforms),
* smallPassenger, smallBoat, tug, yacht, and fishing classes are grouped into smallBoat (small size ships),
* oilTanker and tanker classes are grouped into tanker (common tanker group),
* generalCargo, bulkCarrier, and oreCarrier are grouped into generalCargo (cargo ships),
* cruiser, frigate, patrolForce, and destroyer are grouped into destroyer (combat navy ship group).