Pure rotational Raman lidar measurements of atmospheric temperature near ground in Beijing
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摘要: 对流层大气温度的垂直分布特征直接关联天气现象和大气污染物扩散，一直是气象和环境部门的重点观测对象。当前激光雷达技术已经成为探测对流层大气温度垂直分布和时间演变的有效手段。然而由于对流层中含有大量的气溶胶粒子，因此利用传统的振动拉曼和瑞利散射激光雷达技术测量大气温度具有一定的局限性，尤其是边界层内存在高浓度的气溶胶粒子会严重降低大气温度测量精度。采用纯转动拉曼激光雷达技术可有效降低气溶胶粒子对测量温度精度的影响。纯转动拉曼测温激光雷达的核心是分光单元设计，国内外研究普遍使用基于双光栅干涉仪的分光方法。文中将采用基于滤光片法的纯转动拉曼信号分光设计，相比而言该方法具有更高的分光效率，并且能够通过调节滤光片的角度改变激光雷达系统的灵敏度，操作更为简单。在中国科学院大气灰霾追因与控制先导专项支持下，该激光雷达与2014年11月安置在中国科学技术大学超级大气观测站。在亚太经济合作组织北京会议期间，展开大气环境测量试验。激光紫外波段能量约为200 mJ，频率为20 Hz，激光脉冲数为5 000发，空间分辨率为7.5 m。实验结果表明，在晴朗无云气溶胶浓度较小的天气条件下温度测量统计误差小于1.5 K，测量高度可达10 km，在7.5 km以下统计误差小于1 K；在有薄云或者轻度雾霾天气条件下，温度测量统计误差在3 K左右，测量有效高度通常在6~8 km，在4.8 km以下统计误差小于1 K。Abstract: The vertical distribution of the atmospheric temperature in the troposphere is directly related to the meteorological phenomena and the diffusion of atmospheric pollutants. It has been the major parameters observed by the meteorological department and the environment sector. The lidar technology has become an effective method to detect the vertical distribution and time variation of the atmospheric temperature in the troposphere. Lower tropospheric temperature profile measured by lidar using the Rayleigh and vibrational Raman scattering can't be obtained accurately due to the abundant aerosols. Using N2 and O2 molecular pure rotational Raman scattering signal, the lower tropospheric temperature profile can be obtained without the influence of lower tropospheric aerosol theoretically. The main difficulty of the rotational Raman lidar is design and mechanics of the receiving spectroscopic system. In domestic research, most of the lidar systems use the spectroscopic technique based on double grating spectrometer. The technique based on the interference filters was introduced in this paper and used in our lidar system for observation of the tropospheric temperature. This technique had more efficiency and suppression in separation of the pure Raman signals from Mie signals. Furthermore, the system's sensitivity can be optimized by selecting the tilting angle of the filters. The experiment was based on the project of Formation Mechanism and Control Strategies of Haze in China carried out by the research groups of the Chinese Academy of Sciences. Our lidar system was moved to the super atmospheric observatory in University of Chinese Academy of Sciences on November 2014 and the experiment were taken during the APEC conference. The energy of laser in ultraviolet was about 200 mJ, the frequency was 20 Hz, the laser pulse number was 5 000, the spatial resolution was 7.5 m. The experimental result shows that the statistical error between lidar and radiosonde are less than 1.5 K with the range up to 10 km and the statistical error of less than 1 K is obtained up to 7.5 km height in the clean night. Larger differences of about 3 K at the region above the thin cloud may be caused by the strong elastic backscatter signal and the statistical error of less than 1 K is obtained up to 4.8 km height.
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Key words:
- lidar /
- pure rotational Raman /
- tropospheric temperature /
- interference filters
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