【摘要】 激光雷达近场信号的重叠因子校正和盲区问题一直制约着激光雷达的实用化进程，在假设水平大气均匀的情况下，提出了Mie散射激光雷达的近场信号垂直扫描校正方法和多角度反演算法，实现了大气状态自适应控制遥感。从散射型激光雷达方程出发，构建了激光雷达近场的重叠因子和盲区的模型，结合研制的二维扫描激光雷达参数，仿真分析了重叠因子和盲区的特征。利用Fernald气溶胶反演算法，提出了基于信噪比的多仰角扫描控制与校正方案，以实现不同大气状态的自适应扫描控制。融合多角度扫描遥感数据，并以水平探测的Collis法反演的结果作为地面消光系数，获得了大气气溶胶消光系数无盲区廓线，验证了方案的有效性。数据分析结果表明，在静稳天气时水平能见度优于18 km的情况下，以信噪比20为阈值，通过7个仰角约15 min观测，可实现激光雷达重叠因子的自适应校正，获得的重叠因子校正曲线与水平校正法的平均相对偏差约20%，两组扫描校正的重叠因子的平均相对误差为4.2%，可实现大气气溶胶的无盲区反演。更多还原

【Abstract】 Objective Mie scattering lidar is a remote sensing instrument with a high spatial and temporal resolution, and it has received extensive attention in research since it has successfully been applied in the fields such as atmospheric aerosol observation, cloud and fog characteristic analysis, and pollution emission monitoring. However, most of these groundbased lidars belong to the monostatic structure with the same transmitting and receiving sites. While they are been utilized to detect tropospheric or boundary layer, the transmitting and receiving coaxial systems(limited by the reflective telescope structure) or the transmitting and receiving systems with different axes(also known as off-axis) are almost affected by the near-field blind area and overlap factor, which results in the loss of near-field signals of the lidar or the reduction of accuracy. Therefore, the data of near-field point-type probing instruments(such as horizontal visibility meter, PM2. 5 meter, and particle spectrometer) are usually required for data correction, compensation, or verification in these applications of lidar. However, the near-field atmospheric characteristics are usually essential data in meteorological, environmental, and other fields, which greatly limits the engineering and application process of the lidar.Therefore, overlap factor correction of lidar near-field signals and blind area have always restricted the practical process of lidar.Methods Based on the assumption of horizontal atmosphere uniformity, a multi-angle scanning near-field signal adaptive correction method for lidar is proposed using the vertical scanning function of the developed two-dimensional scanning lidar system. Firstly, according to the overlap factor model of an off-axis lidar system, the influence of laser beam divergence angle, telescope field angle, optical axis distance, and optical axis angle on the overlap factor is analyzed. Secondly, using the Fernald aerosol retrieval algorithm and taking the advantage of lidar vertical scanning, a multi-elevation angle correction scheme dependent on signal-to-noise(SNR) threshold is proposed to achieve adaptive scanning control of different atmospheric states. Combined with the ground extinction coefficient retrieved by the Collis method and the multiangle scanning remote sensing data, the aerosol extinction coefficient without a blind area profile is retrieved, and the effectiveness of the correction scheme under different weather conditions is compared.Results and Discussions Based on the stratification assumption of a uniform atmosphere, the multi-elevation angle scanning control and correction steps(Figs. 5 and 6) are designed to realize the adaptive scanning control for different atmospheric states. Using multi-angle scanning remote sensing data and taking the result of Collis retrieval by horizontal detection as the ground extinction coefficient, the blind area profile of the atmospheric aerosol extinction coefficient is obtained [Fig. 7(c) and Fig. 8(c)]. When the horizontal visibility is better than 18 km and the SNR threshold is 20, the average relative deviation of the overlap factor correction curve and the correction curve of the horizontal detection method is about 20% [Fig. 7(d) and Fig. 8(d)], and the average relative error of the overlap factor curve is 4. 2%(Fig. 9).Finally, a group of data with 24-h observation is shown to verify the scanning correction method(Fig. 10), and the retrieval without blind area of atmospheric aerosol can be realized.Conclusions In order to correct the near-field aerosol extinction profile of ground-based Mie scattering lidar, a vertical scanning correction method and multi-angle retrieval algorithm are proposed for near-field signals of Mie scattering lidar,and then the adaptive control of the atmospheric state is probed based on the assumption of horizontal atmosphere uniformity. Owing to the scattering lidar equation, a model of the overlap factor and blind area in the near field of the lidar is constructed, and the characteristics of the overlap factor and the blind area are analyzed and simulated based on the developed two-dimensional scanning lidar. In combination with the Fernald retrieval algorithm, a multi-elevation scanning control and correction scheme dependent on SNR is presented to realize adaptive scanning control for different atmospheric conditions. The profile of atmospheric aerosol extinction coefficient without blind area under different weather conditions is obtained by merging multi-angle scanning remote sensing data and the ground extinction coefficient obtained by the Collis method of horizontal detection, and the effectiveness of this scheme is verified. The data analysis results show that the adaptive correction of the lidar overlap factor can be achieved through seven elevations of about 15-min observation with the SNR ratio of 20 as the threshold when the horizontal visibility is better than 18 km. The mean relative deviation of the obtained calibration curve from horizontal correction is about 20%, and the mean relative error of the correction results of the overlap factor curves is 4. 2%, which can realize the retrieval of atmospheric aerosol without blind area.更多还原