| 用于烟尘监测的偏振激光雷达系统及实验研究 |
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| 引用本文： | 徐文静,冼锦洪,孙东松.用于烟尘监测的偏振激光雷达系统及实验研究[J].红外与激光工程,2023,52(3):20220508-1-20220508-10. |
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| 作者姓名： | 徐文静 冼锦洪 孙东松 |
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| 作者单位： | 1.中国科学技术大学 地球和空间科学学院，安徽 合肥 230026 |
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| 基金项目： | 国家自然科学基金(41774193) |
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| 摘 要： | 激光雷达具有探测距离远，分辨率高，对气溶胶浓度变化敏感等优势，偏振激光雷达还能够对粒子形态做区分，根据消光系数及退偏比值识别云、雾、烟尘等。利用偏振激光雷达进行扫描观测，可以实现火灾烟尘的快速识别。通过对不同波长的激光雷达探测距离进行仿真，结果表明，波长为1 064 nm的激光雷达探测距离为532 nm波长的1.3～1.4倍。通过优化扫描策略及算法，可剔除固定障碍物及临时移动障碍物的影响。为避开安装点位周边高度相近的障碍物，通常会给激光雷达设置一定仰角，对存在探测仰角时产生的水平距离偏差及垂直高度测量偏差进行计算，当激光雷达探测仰角为2°时，6 km处测量高度偏差为209.397 m。使用高斯烟羽模型对烟尘浓度分布进行仿真，当大气稳定度为B，平均风速为1 m/s时，200 m高度处烟尘浓度分布高值点距地面火点的径向距离≥1 km，为火点准确定位提供了修正依据。分别在辽宁省盘锦市盘山县绕阳湖景区，广东省东莞市观音山森林公园进行外场实验，偏振激光雷达在开阔地带及多障碍物山体地带下，均能够快速识别烟尘。
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| 关 键 词： | 偏振 激光雷达 退偏比 遥感 烟火监测 |
| 收稿时间： | 2022-07-21 |
Polarization lidar system for smoke and dust monitoring and experimental research |
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| Affiliation: | 1.School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China2.School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China |
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| Abstract: | Objective The fires in forests, wetlands, grasslands and other natural areas are characterised by their sudden and destructive nature, and it is important to reduce the damage caused by fires through early detection and fighting. Traditional fire monitoring methods such as manual inspections and cameras do not allow for 24/7, wide-area monitoring, and there is a lag in detecting fires. Therefore, the use of lidar with high precision, high resolution, long detection distance and sensitivity to changes in aerosol particle concentration, etc., can play an important role in the field of smoke and fire monitoring, to achieve early detection and early warning of fire. Researchers have made some explorations in this area. However, for lidar detection distance of 2 km or more, the single pulse energy of the laser was on the order of millijoule, and there is a human eye safety risk for outdoor use. Moreover, the researchers have not given an analysis of the measurement and application in a multi-obstacle environment. Therefore, a polarimetric lidar system with a day and night detection, and detection distance of more than 6 km and the single pulse energy of the laser on the order of microjoule is proposed. Methods Laser wavelengths adapted to outdoor long-range detection are obtained through simulations. The lidar scanning strategies are designed for different installation scenarios, for flat environments and for environments with many obstacles, respectively. As the lidar measurement areas are at a certain height from the ground, correction for fire point positioning errors is based on a Gaussian plume model. A portable lidar system with polarization channels was built to further validate the simulation results, scanning control strategies and inversion algorithms through field experiments. Results and Discussions By simulating the detection distance of lidar with different wavelengths, the results show that the detection distance of lidar with 1 064 nm wavelength is 1.3-1.4 times of 532 nm wavelength (Fig.2). By optimizing the scanning strategy and algorithm (Fig.4), the influence of fixed obstacles and temporary moving obstacles can be eliminated. In order to avoid obstacles of similar height around the installation site, a certain elevation angle is usually set for the lidar, and the horizontal distance deviation and vertical height measurement deviation resulting from the existence of the detection elevation angle are calculated. When the elevation angle of lidar detection is 2°, the measured height deviation at 6 km is 209.397 m. The Gaussian plume model is used to simulate the soot concentration distribution. When the atmospheric stability is B and the average wind speed is 1 m/s, the high value point of soot concentration distribution at 200 m height is ≥1 km from the ground fire point, it provides a correction basis for accurate location of fire point. Outfield measurements by using 1 064 nm polarization lidar in both mountainous and plain environments can quickly and accurately identify fire points, which demonstrate the feasibility of using lidar for smoke and fire monitoring. Conclusions A scanning polarization lidar can rapidly identify fire smoke and dust. The field experiments were conducted in Panshan County, Panjin City, Liaoning Province, around Yanghu Scenic Area, and Guanyin Mountain Forest Park, Dongguan City, Guangdong Province, respectively. The polarization lidar was able to identify the smoke and dust quickly under the open area and multi-obstacle mountainous area. Observational data will be accumulated in subsequent experimental tests to verify the optical properties of various types of soot particles and further improve the identification efficiency. |
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