| 海洋激光雷达测量水体剖面偏振信号的仿真模拟 |
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| 引用本文： | 李珂,刘秉义,杨倩,唐军武,吴松华. 海洋激光雷达测量水体剖面偏振信号的仿真模拟[J]. 红外与激光工程, 2021, 50(6): 20211035-1-20211035-10. DOI: 10.3788/IRLA20211035 |
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| 作者姓名： | 李珂 刘秉义 杨倩 唐军武 吴松华 |
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| 作者单位： | 1.中国海洋大学 信息科学与工程学部，山东 青岛 266100 |
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| 基金项目： | 国家重点研发计划（2016YFC1400905，2016YFC1400904） |
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| 摘 要： | 基于蒙特卡洛模拟方法，建立了一个水中激光偏振辐射传输模型，用于模拟分析船载偏振激光雷达水体垂直剖面的偏振探测回波，分析了不同光学参数的水体和激光雷达测量模式下的偏振测量误差。使用高斯分布设置了三种深度分布在10~30 m的低、中、高浓度散射层，其叶绿素a峰值浓度分别为0.1 mg/m3、1 mg/m3和10 mg/m3。模拟了激光发射波长为532 nm，接收视场角为10~1000 mrad的船载海洋激光雷达的偏振回波信号，并分析了影响偏振测量误差的主要因素。研究结果表明，由于激光在水中的多次散射过程，随着探测深度、叶绿素a浓度和接收视场角的增大，激光雷达接收光信号的单次散射率不断降低，导致激光雷达直接测量的退偏振比的误差随之增大。以100 mrad接收视场角为例，中浓度散射层情况下，在散射层上（0~10 m）、散射层中（10~30 m）和散射层下（30~40 m）的退偏振比相对误差分别为16%、125%、281%；在散射层中，低、中、高三种浓度散射层的退偏振比相对误差分别为54%、125%、731%。视场角从10 mrad增大到1000 mrad时，退偏振比相对误差逐渐增大，在中浓度散射层情况下，其在散射层上、散射层中和散射层下的变化范围分别为6%~28%、17%~452%和10%~734%。文中结果表明，偏振海洋激光雷达探测水体退偏振比时，由于多次散射过程的影响，传统的退偏振比算法会引入较大误差，有必要在反演算法中对其进行校正，以提高激光雷达的探测精度。
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| 关 键 词： | 海洋激光雷达 偏振蒙特卡洛 水体光学参数 垂直剖面 退偏振比 |
| 收稿时间： | 2021-05-06 |
Simulation of polarization profiles of water measured by oceanographic lidar |
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| Affiliation: | 1.Faulty of Information Science and Engineering, Ocean University of China, Qingdao 266100, China2.Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China3.Institute of Oceanographic Instrumentation, Qilu University of Technology (Shandong Academy of Sciences), Qingdao 266071, China |
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| Abstract: | A Monte Carlo radiative transfer model with polarization was developed to simulate and analyze the vertical profile of received polarization signal of a ship-borne lidar. The measurement errors resulted from different seawater optical parameters and various lidar measurement modes were analyzed as well. A Gaussian distribution function was used to describe the chlorophyll-a vertical profile. The scattering layers were set at 10-30 m with the low, medium and high values of chlorophyll-a concentration ([chl-a]), respectively, and the corresponding maximum value of [chl-a] was 0.1 mg/m3, 1 mg/m3 and 10 mg/m3, respectively. The polarization return signals of the ship-borne oceanographic lidar were simulated with a laser transmission wavelength of 532 nm and field of views (FOVs) of 10-1000 mrad, and the main factors affecting the polarization measurement error were analyzed. The results suggest that the single scattering ratio of lidar return signal decreases with the enhancements of detection depth, [chl-a] and FOV due to the multiple scattering process of laser transferring in seawater. This leads to an increase in the error of the depolarization ratio directly measured by lidar. Let’s take the FOV of 100 mrad as an example. In the case of the scattering layer with a medium [chl-a], the relative errors of the depolarization ratio above (0-10 m), in (10-30 m) and under (30-40 m) the scattering layer were 16%, 125% and 281%, respectively. In the scattering layer, the relative errors of the depolarization ratio were 54%, 125% and 731% for the low, medium and high values of [chl-a], respectively. When the FOV increases from 10 mrad to 1000 mrad, the relative error of the depolarization ratio increases from 6%-28% above the scattering layer, 17%-452% in the scattering layer and 10%-734% under the scattering layer, respectively, for the case of the scattering layer with a medium [chl-a]. Therefore, when using the polarization oceanographic lidar to detect the seawater depolarization ratio, the traditional algorithm for depolarization ratio will introduce a large error due to the multiple scattering process, and a correction is required to improve the detection accuracy of lidar measurement. |
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