## 4 Experimental Results and Discussion
### Overall Detection Performances
The precision of the methods from [13; 17] is high with respect to calm sea surfaces, but for complex sea surfaces, detection performance is greatly reduced, as shown in Table 3. The method proposed in this paper is optimal for detection accuracy. On average, the detection time of our method is 1.6 s. The efficiency of our algorithm is not the highest. Compared with the method from [13], which has comparable accuracy, our efficiency is almost double. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Different Situations** & **Accuracy** & **FA** & **MA** \\ \hline Calm sea & 98.10\% & 1.90\% & 1.43\% \\ Textured sea & 93.40\% & 6.60\% & 5.43\% \\ Clutter sea & 86.80\% & 13.20\% & 10.88\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Detection results of our method in various situations. Figure 14: Cont. Figure 14: Detection results of images from the satellites ZY-3 and GY-2. (**a**) Detection results of cloud and wave coexistence. (**b**) Detection results of thick cloud interference. (**c**) Detection results of mist interference. (**d**) Detection results of strong wave interferences. (**e**) Detection results of a calm sea surface. (**f**) Detection results of very low contrast. (**g**) Detection results of middle-size ships with wakes and wave interference. (**h**) Detection results with thick cloud occlusion. Figure 15: _Cont._  
A linear function combining pixel and region characteristics was employed to select ship candidates in [7]. When the background was covered by clouds, the location of ROIs would fail, resulting in missed alarms. Compactness and the length-width ratio were considered to remove false alarms. The description features were not enough to distinguish between targets and background when the background became complex. The detection performance was greatly reduced. Regarding the calm sea, the method in [17] achieved the best performance. The accuracy was 98.3%, and the false and missed alarm rates were very low. However, this method only adopted intensity distinctness to find ROIs and led to omissions in complex backgrounds. In the false alarm exclusion stage, the LBP histogram features of the bow, stern, left hull, and right hull were used. The algorithm could achieve better results in distinguishing large ships from false alarms, but when the ships were small or the background became complex, the false alarm rate was higher, because there was little difference between each \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Method** & **Accuracy** & **FA** & **MA** & **Time Consumed** \\ \hline Method from [7] & 80.2\% & 19.8\% & 20.3\% & 1.2 s \\ Method from [17] & 83.9\% & 16.1\% & 11.1\% & 1.5 s \\ Method from [13] & 88.4\% & 11.6\% & 7.3\% & 3.1 s \\ Our method & 92.8\% & 7.2\% & 5.9\% & 1.6 s \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average detection performance of different methods. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Method** & **Different Situations** & **Accuracy** & **FA** & **MA** \\ \hline \multirow{3}{*}{Method from [7]} & Calm sea & 92.20\% & 7.80\% & 4.40\% \\  & Textured sea & 81.30\% & 18.70\% & 12.40\% \\  & Clutter sea & 67.00\% & 33.00\% & 44.20\% \\ \hline \multirow{3}{*}{Method from [17]} & Calm sea & 98.30\% & 1.70\% & 1.40\% \\  & Textured sea & 83.20\% & 16.80\% & 6.70\% \\  & Clutter sea & 70.20\% & 29.80\% & 25.20\% \\ \hline \multirow{3}{*}{Method from [13]} & Calm sea & 97.30\% & 2.70\% & 1.80\% \\  & Textured sea & 85.30\% & 14.70\% & 5.60\% \\ \cline{1-1}  & Clutter sea & 82.60\% & 17.40\% & 14.60\% \\ \hline \multirow{3}{*}{Our method} & Calm sea & 98.10\% & 1.90\% & 1.43\% \\ \cline{1-1}  & Textured sea & 93.40\% & 6.60\% & 5.43\% \\ \cline{1-1}  & Clutter sea & 86.80\% & 13.20\% & 10.88\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Detection results of different methods in various situations. Figure 15: Detection results of images from Google Earth. (**a**) Detection results of cloud occlusion. (**b**) Detection results of a little cloud interference. (**c**) Detection results of the inland lake.