# Research on Laser Dual-Mode Fusion Detection Method of Ship Wake Bubbles
## 2 Ship Wake Bubbles Laser Detection Characteristics and Analysis
### Technology and Characteristics of Ship against Wake-Guided Weapons  
In the process of the development of underwater-guided weapons, the methods of countering underwater-guided weapons are also constantly developing. In order to effectively avoid attacks from underwater weapons, surface ships will change the wake path to resist the attack creating false wakes, steering avoidance, cross tracks, and so on [20; 21]. Now, the wake characteristics of the more complex manufacturing of false wakes and cross tracks are analyzed.  
(1) Creating false wake deception jamming  
When the surface ship is captured by underwater weapons, the surface ship can launch air curtain bombs to simulate one or more false wakes that are connected to the wake track of the ship but go in different directions, luring the underwater weapons away from the real wake zone. The main diagram is shown in Figure 1. The width and thickness of the false wake manufactured by it have obvious changes to the real wake. The specific wake change is that the number of bubbles increases sharply at 1, 2, 3, and 4 of the wake, the thickness of the bubbles does not change much, and the range of bubble scale changes and expands. If the detection system has the ability to analyze and detect the number density and scale of bubbles, it can resist the false wake of artificial air curtain bombs. According to the authors of [22], it can be seen that the change in bubble number density and scale can be identified by the change in echo intensity and saturation depth of the laser detection system, and the reliability of true and false wake identification can be further improved by combining laser imaging detection.  
(2) Annular wake interference  
When the surface ship is captured by the underwater weapon, the surface ship can form a cross wake by turning 270\({}^{\circ}\) to trap the incoming weapon. The main schematic diagram is shown in Figure 2. The number of bubbles in the annular wake created by it  
Figure 1: False wake confrontation form:(1) Wake junction; (2) Wake junction; (3) Wake junction; (4): Wake junction.  
increases sharply at 1, the thickness of the bubbles increases, and the range of the bubble scale expands. If the detection system has the ability to analyze and detect the bubble number density, thickness and scale, it can resist the annular wake. Similarly, the change in bubble number density, thickness, and scale can be identified by the change in echo intensity and saturation depth of the laser detection system, and the reliability of true and false wake identification can be further improved by combining laser imaging detection.  
In the application of anti-artificial false wakes and ship cross-annular wakes, if only the laser adaptive backscattering detection mode is used, it will be limited by the detection range and cannot reliably resist false wakes and annular wakes. If only the laser imaging detection mode is used, it will be limited by the speed of image processing algorithms and target detection, and cannot effectively track the ship. By combining the advantages of the two detection methods, the laser backscattering detection is used to track the ship wake, and the laser imaging method is used to assist the large field of view detection and discriminate against the wake form. The laser backscattering detection mode is combined with the laser imaging detection mode, which can further improve the detection SBR of the ship's wake echo signal and suppress the influence of seawater backscattering on the detection system.