In recent years, with the rapid increase in military and civilian demand and the rapid development of optoelectronic technology,Airborne lidar is increasingly being applied to airborne platforms, once again becoming a new research hotspot.
1 Lidar classification
According to the detection technology used at work, lidar can be divided into direct detection and coherent detection: according to the functions of the lidar, it can be divided into tracking lidar, moving target indicator lidar, and wind shear detection laser Radar, target recognition lidar, vibration sensing lidar and imaging lidar.
2 Machine-cut lidar applications
Airborne lidar has broad potential and prospects in many fields for military and civilian use.
Low-altitude and ultra-low-altitude obstacles, such as towers, high poles, electrical wires, and blocking balloon cables, are serious threats to airplanes and helicopters flying, but the sensors on previous airplanes, including the naked eye and radar, have found it difficult to find the above obstacles. Especially at night and under bad weather conditions. Lidar has a higher angular resolution, can work at night, and can also draw three-dimensional images of obstacles. The image information provided is sufficient to identify targets. Therefore, an important application of Lidar on airplanes and helicopters is low altitude and ultra-low altitude. Obstacle early warning also has more advantages than existing radar systems for the detection of small targets at sea.
The United States, Germany, France and other countries have developed aircraft and helicopter flight obstacle avoidance systems]. As early as the end of the 20th century, the German "Hel las" obstacle detection lidar was able to detect wires with a diameter of more than 1 cm within a distance of 300 and 500 meters. The French pod-mounted CLARA lidar can not only detect obstacles such as poles and cables, but also has functions such as terrain tracking, target indication and ranging, and active target indication.
Especially when lidar is combined with other remote sensing technology and global positioning system (GPS) technology into a lidar ranging system, which can provide distance information of ground objects, plus the aircraft platform attitude information provided by the aircraft inertial measurement unit, the ground can be obtained. The three-dimensional coordinates of the object. The target intensity information obtained by lidar is combined with the image information obtained by other airborne remote sensing instruments, which can be used as spectral data for ground object analysis. Therefore, the airborne integrated system with lidar participates in aerial reconnaissance, anti-submarine, surveying and mapping, and exploration. And detection field has broad application prospects. The 3D geographic information rapid acquisition system integrating laser scanning ranging technology, GPS positioning technology, inertial navigation technology, image processing technology and digital photogrammetry technology is currently a new and sharp detection system, namely Airborne Lidar (Airborne Lidar) Light Detection And Ranging-Airborne LiDAR) technology can provide low-cost, fast, high-density, high-precision digital surface data or digital elevation data, so it has become a popular high-tech in various measurement applications and has huge applications In the future, it has very important theoretical value and practical significance to carry out research on the accuracy of airborne LiDAR data.
Since the energy of electromagnetic waves transmitted in the water decays rapidly, the previous underwater detection mainly used sonar equipment. Using blue-green pulsed lidar, underwater detection and mine search can be realized. The US military’s "Magic Lantern" mine detection laser Zuda system and Sweden’s "flashlight" and "Eagle Eye" airborne marine lidars have been successful airborne underwater detection systems. Kaman Aerospace Corporation of the United States has developed an airborne underwater imaging lidar, which can image underwater targets and display features such as the shape of underwater targets to facilitate target identification. At the same time, a single laser pulse of imaging lidar covers a large area, so the search efficiency is much higher than that of non-imaging lidar, which becomes a major advantage of imaging lidar. In 2002, the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences developed and improved on the basis of the first-generation airborne laser sounding system, which can simultaneously detect the seabed and the sea surface.
Lidar can obtain three-dimensional image information and speed information of the target, which is convenient for identifying stealth targets. It can also be used to measure the trajectory of various flying targets, such as tracking and measuring missiles and rocket initial stages, and low-elevation tracking and measurement of aircraft and cruise missiles.
The combination of lidar and computer can automatically recognize another target, and provide reliable target speed information, and target characteristic information to distinguish special targets, thereby improving weapon targeting accuracy, as a very important device for automatic and semi-automatic targeting systems At present, Lidar is more and more popular.
The energy attenuation of laser in the atmosphere is large, and the absorption and scattering of hydrometeors and particulate matter in the atmosphere will greatly reduce the range of lidar. Therefore, lidar can be used to monitor the atmospheric environment or use the interaction of laser with particulate matter and chemical agents for remote sensing Detect air pollution and chemical warfare agents. Atmospheric Lidar has a fine spatial resolution, time continuity, and high detection accuracy, and it has positive practical significance for real-time monitoring of changes in the atmospheric composition of the boundary layer (0, 2 kilometers) and analysis of the structural characteristics of the atmosphere. The meter scattering lidar can be used to monitor atmospheric aerosols and clouds.
Through the principle of coherent detection, airborne lidar can detect wind shear and clear sky turbulence, reduce the serious threat of wind shear and clear sky turbulence during takeoff and landing phases, and improve the safety and survivability of the aircraft. Lidar can also perform direct Doppler detection of the atmospheric wind field and map ballistic wind, which is of great significance for reducing and correcting the interference of wind on bomb dropping.
In addition, use airborne lidar data to retrieve important parameters such as atmospheric temperature and humidity.
3 Limitations and difficulties of airborne lidar The main limitations of lidar are as follows.
1) The detection range is short. When the laser is transmitted in the atmosphere, the energy is attenuated by the influence of the atmosphere. The range of the laser radar is within 20 kilometers; especially under severe weather conditions, such as dense fog, heavy rain, smoke, and dust. Will be greatly shortened and difficult to work effectively. Atmospheric turbulence will also reduce the measurement accuracy of lidar to varying degrees.
2) Because the receiving aperture of lidar is small and the beam is too narrow, the search space is also small, and it is difficult to quickly search and coarsely capture the target. Other equipment should complete the above work. Therefore, the airborne lidar cannot completely replace the traditional radar and is mostly used as a supplement to the ordinary radar.
For the realization of airborne lidar systems, there are still some key technologies that need to be further strengthened and improved, such as:
1) Space scanning system and method technology. The space scanning system of lidar is divided into non-scanning and scanning systems. Under the scanning system, there are mechanical scanning, electrical scanning, and binary optical scanning. To achieve different functional tasks, it is necessary to study the corresponding specific technical applications. The non-scanning system uses multiple sensors to make the equipment smaller in weight and volume and has a longer range. It is an ideal technology for airborne. However, because the required multiple sensors are not easy to obtain, it is currently difficult to quickly realize engineering applications in China. 2) The development of lasers. Most of the semiconductor lasers, semiconductor pumped solid-state lasers and gas lasers currently used have their own advantages and disadvantages, and further improvement and development are still needed.
3) Receiver design, the characteristics of the airborne lidar, and the working environment determine that the receiving unit’s receiving sensitivity requirements are getting higher and higher while requiring high echo detection probability and low false alarm rate. These all require continuous improvement and Develop new technologies.4 Development trend of airborne lidar applications
Since lasers first came out in the late 1960s, lidar technology has always been a technology that countries all over the world are vying to master and develop. At present, lidar is still under development, and the application of airborne lidar systems is gradually realizing practical use, and other lidar applications are being developed and explored. Compared with developed countries, the application research of airborne lidar technology in my country started late, and the degree of development is still relatively backward, in order to promote airborne laser yaw. The stop signal conditions for unmooring left yaw and unmooring right yaw are the same.https://www.isurestar.net/