Objective In order to meet the tactical requirements of modern naval warfare, air-to-air missiles should be capable of intercepting ultra-low altitude sea-sweeping flight targets such as anti-ship missiles and cruise missiles. At present, the advanced level in the world has been able to fly at a height of 3 m above the sea. In this case, the complex sea background clutter will not only affect the detection and tracking of the missile guidance system to the target, but also enter the range of the fuze at the end of the rendezvous phase, which will seriously affect the fuze work, leading to false alarm or reduced starting ability. Therefore, improving the ability of fuze to resist ultra-low altitude sea background interference has always been a research focus to expand its battlefield adaptability. At present, conventional laser fuzes use multi-quadrant zonal wavegate compression, dual-beam detection and other technologies to suppress sea clutter, but each has certain application limitations. In this paper, a low altitude sea background target recognition method based on digital laser imaging is proposed. This method is based on the difference of imaging characteristics between the sea level and the physical target in the space distribution, and uses the fine recognition ability of laser imaging to the echo characteristics of different azimuth angles, which can improve the adaptability of proximity fuze to work reliably in the ultra-low altitude sea environment.
Methods The dynamic sea surface laser echo simulation system is established to obtain the laser scattering characteristics of sea level and target. The simulation system can set the field angle parameters of the laser imaging system, and can obtain the echo signal characteristics under different intersection conditions and different sea conditions in real time. The scattering model of sea surface panel segmentation is used to calculate the laser echo distribution characteristics under different detection field angle parameters. The simulation flow chart is shown (Fig.1). Through the statistics and analysis of the distribution characteristic data of the laser scattering echo on the sea surface, a target recognition method based on the laser imaging system for low altitude sea background is designed and verified by simulation.
Results and Discussions In terms of target characteristic simulation, for the imaging detection system that uses spatial narrow field of view subdivision, due to the undulation of the sea surface, the sea surface echo presents discrete flicker feature in the spatial distribution (Fig.5), which is significantly different from the imaging feature of continuous solid targets (Fig.6) in the spatial distribution. In terms of target recognition method design, a circumferential 360° solid-state array laser high-speed scanning detection system is proposed, and full digital echo signal processing is realized through high-speed AD sampling. According to the characteristics of high-speed rendezvous between missile and target, a method of low altitude sea background target recognition based on intra-frame judgment and inter-frame accumulation is proposed. This method can quickly filter out the sea background clutter by means of straight-through filtering, mathematical morphology filtering, target morphology features and other methods to ensure the real-time and reliability requirements of missile-borne detection and recognition. The average recognition accuracy of this method under different sea conditions is 96.9% (Tab.2) through simulation verification of different intersection conditions.
Conclusions In this paper, a target recognition method based on digital array laser scanning imaging is proposed. This method can realize circumferential 360° solid state scanning detection through the time-sharing and high-speed operation of the electronically controlled array laser, and digitize the echo imaging features through high-speed AD sampling. It has the characteristics of fast recognition speed and high degree of digitalization, and can meet the real-time requirements of high-speed target recognition. The digital modeling of sea surface and laser detection has been carried out, and the optical reflection characteristics of sea clutter have been simulated and analyzed. Based on the target characteristics, a low-altitude sea background target recognition method of intra-frame judgment and inter-frame accumulation has been designed. Through simulation and test verification, the average recognition accuracy of this method under different sea conditions is 96.9% (Tab.2). The relevant technologies in this paper can provide methods and ideas for laser fuze anti-low altitude sea environment interference technology.
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