## 5 Results and Analysis of Experiment  
### Rainfall Detection Results  
Firstly, a randomly selected radar image is detected by the RZE method. The fan-shaped area (azimuth 50\({}^{\circ}\) to 100\({}^{\circ}\) and radial 80 points to 600 points) and the fan-shaped area (azimuth 150\({}^{\circ}\) to 200\({}^{\circ}\) and radial 80 points to 600 points) of the selected radar image are taken as the occlusion area and the wave area for rainfall detection, as shown in Figure 11.  
The ZPP and \(\mu\) of the occlusion area of the selected radar image are calculated as 46.15% and 0.3814 V, respectively, and the RZE calculated by the Equation (5) is 121.0015 (\(V^{-1}\)). Since the RZE is lower than the threshold T determined in Section 4.1, the selected radar image is rain-contaminated radar image. The rainfall intensity automatically recorded by the rain gauge is 0.4 mm/10 min. Therefore, the result of rainfall detection is correct. Additionally, the ZPP and \(\mu\) of the wave area of the selected radar image are calculated as 34.12% and 0.4778 V, respectively, and the RZE calculated by the Equation (5) is 71.4106 (\(V^{-1}\)). Since the RZE is lower than the threshold K determined in Section 4.1, the selected radar image is rain-contaminated radar image, and the result of rainfall detection is also correct. Then, in order to further demonstrate the rainfall detection performance of the proposed method, the RZE method and the traditional ZPP method are studied together. The X-band marine radar collects a group of radar image sequence every 3 min, and each group of radar image sequences contains 32 radar images. The first radar image in each group of image sequences is selected for rainfall detection. A total of 360 radar images are selected, including 160 rain-free radar images and 200 rain-contaminated radar images, as shown in Figure 12. The blue solid line with stars denotes the rainfall intensity, and the unit of rainfall intensity is mm/10 min. The rainfall detection results of the X-band marine radar images are shown in Figure 13. Figure 13 shows the performance of the traditional ZPP method for rainfall detection. The blue solid line denotes the curve trend of the calculated ZPP, and the selected area with green solid line denotes the radar image in the presence of rainfall. The red dotted line denotes the determined detection threshold proposed by [PERSON] et al. Figure 13b shows the performance of the RZE method for rainfall detection. The blue solid line denotes the curve trend of the calculated RZE, and the selected area with green solid line denotes the radar image in the presence of rainfall. The red dotted line denotes the detection threshold of the RZE method, which is determined in Section 4.1. It can be seen from Figure 13a,b that the blue curves of the two methods are almost lower than the detection threshold in the range of rainfall, which indicates that both methods have excellent rainfall detection performance. Among the 200 rain-contaminated  
Figure 11: The selected radar image. radar images, 200 images are detected by the traditional ZPP method and 188 images are detected by the RZE method. The detection accuracy of the traditional ZPP method is slightly higher than that of the RZE method, and both methods meet the engineering requirements. In addition, among 160 rain-free radar images outside the green solid line, 106 images are detected by the traditional ZPP method and 160 images are detected by the RZE method. The detection accuracy of the RZE method is close to 100%, which is much higher than the traditional ZPP method. Therefore, the total detection accuracy of the RZE method is higher than that of the traditional ZPP method. Figure 12: The rainfall intensity recorded during the experiment. Figure 13: _Cont._  
The detection threshold determined by the ZPP method is different with different radar systems. Based on the actual radar system, the detection threshold of the ZPP method is redefined and discussed.