# Research on Laser Dual-Mode Fusion Detection Method of Ship Wake Bubbles
## 3 Simulation of Ship's Wake Bubble Laser Dual-Mode Detection Based on Monte Carlo
### Simulation of Laser Illumination Imaging Characteristics of Ship Wake Bubbles  
(1) Laser backscattering characteristics of bubbles with different number densities  
According to the above ship's wake distribution model, the passive imaging characteristics of bubbles under different bubble number densities are studied. The bubble number density is set to \(10^{5}\), \(10^{6}\), \(10^{7}\), \(10^{8}\), and \(10^{9}\) m\({}^{-3}\), the bubble layer thickness is 0.3 m, the bubble size is 80 \(\upmu\)m, and the distance is set to 5 m. The bubble imaging simulation is shown in Figure 7, where the blue area is the receiving lens area, and the bubble imaging change is simulated by counting the photons returned to the bubble group. From Figure 7, it can be found that as the bubble number density increases, the number of photons received by the receiving lens gradually increases, and the overall change becomes stronger and stronger. In addition, the photons in the central region become more concentrated and brighter. The number of photons in the circumferential region also increases, but their positions change more randomly. This can also be confirmed by the backscattering simulation of the above ship's wake. From the perspective of imaging,the change is more obvious than the change in backscattering, which can make up for the defect that the amplitude of backscattering change is small when the bubble number density changes to a certain extent. It can also prevent the ship from avoiding underwater weapons by judging the change in bubble number density characteristics. The change in laser backscattering of bubbles with different thickness  
The backward scattering characteristics of bubbles under different bubble layer thicknesses are studied. The bubble number density is set to \(10^{8}\) m\({}^{-3}\), the bubble layer thickness is 0.1, 0.3, 0.5, and 0.7 m, and the other parameters remain unchanged. The bubble imaging simulation diagram is shown in Figure 8.  
From Figure 8, it can be observed that as the thickness of the bubble layer increases, the number of photons received by the receiving lens gradually increases. Additionally, the photons in the central region become more concentrated and brighter, resulting in a stronger overall change. However, the degree of this change is relatively weaker compared to that caused by variations in the bubble number density. Moreover, the number of photons in the circumferential region also increases, but their positions vary randomly. This observation corroborates the aforementioned simulation of backscattering from ships' wakes. From the perspective of imaging, it can also be concluded that bubbles with a large thickness have a greater impact on the detection system, resulting in higher detection sensitivity. The change in laser backscattering of bubbles with different sizes  
The bubble passive imaging characteristics under different bubble number densities are studied. The bubble scale is set to 40, 60, 80, 300, 400, and 500 \(\upmu\)m, and the thickness of the bubble layer is 0.3 m. The other parameters remain unchanged. The bubble imaging simulation is shown in Figure 9.  
Figure 8: Bubble imaging characteristics under different thickness of bubble layer: (**a**) 0.1 m; (**b**) 0.3 m; (**c**) 0.5 m; (**d**) 0.7 m.  
From Figure 9, it can be observed that as the size of the bubbles increases, the number of photons received by the receiving lens gradually increases. Additionally, the photons in the central region become more concentrated and brighter, resulting in a stronger overall change. This change is more significant compared to variations in bubble layer thickness. Furthermore, the number of photons in the circumferential region also increases, but their positions vary randomly. This observation corroborates the aforementioned simulation of backscattering from ships' wakes. From the perspective of imaging, it can be concluded that large-scale bubbles have a greater impact on the detection system compared to microbubbles, resulting in higher detection sensitivity.