拉曼激光雷达测量水汽误差分析研究

发布时间：2018-03-20 17:47

本文选题：拉曼激光雷达　切入点：大气探测　出处：《中国科学技术大学》2017年硕士论文　论文类型：学位论文

【摘要】：在大气中,水汽是一种重要的气象要素,在云物理和降水的形成过程、大气化学反应过程及能量循环过程中发挥着重要作用。水汽是大气中唯一可以相变的气体,水汽的特殊性及其对生命意义的影响,使水汽区别于其他气体而受到人类的广泛关注。作为一种光学主动遥感方法,激光雷达系统具有探测距离远、精度高、灵敏度高、时空分辨率高等优点。因此,激光雷达系统被广泛应用于大气探测、环境监测、气候研究等领域。本文依托自研拉曼激光雷达系统采集数据,计算得出水汽混合比,并对水汽混合比的误差进行分析。依据误差传递理论,逐项分析水汽混合比误差的各个误差源贡献,结果表明:激光雷达测量水汽混合比的误差主要包括标定常数、大气透过率修正和回波信号三个误差源。其中,标定常数误差和系统参数及标定方法息息相关,不随高度而改变,约为4-6%,是1.5公里以下激光雷达测量水汽混合比总相对误差的主要来源;大气透过率修正误差主要源于实际大气光学特性,随高度升高而增加,洁净天气条件下对总相对误差的影响小于4%,污染天气条件下对总相对误差的影响小于5%;回波信号误差和系统参数及大气特性相关,在洁净天气条件下,回波信号误差在垂直高度3公里以下一般小于20%,在垂直高度3公里以上,成为水汽混合比总相对误差的主要来源;在污染天气条件下,回波信号误差在2公里以下一般小于30%,在2公里以上,成为水汽混合比总相对误差的主要来源。由于回波信号的相对误差是水汽混合比总误差中最不确定的部分,为了详细分析激光雷达回波信号的相对误差,分别采用随机误差方法、泊松公式方法和背景信号方法,计算得出水汽混合比的整体误差,并通过激光雷达与无线电探空仪测量水汽混合比的对比实验,分析验证这三种计算回波信号相对误差的方法。结果表明:三种方法各自有的优缺点和适用条件。随机误差方法计算水汽混合比的相对误差时,计算低层几何因子和大气中气象结构的测量结果相对误差偏大。泊松公式方法计算水汽混合比的相对误差时,激光雷达信噪比较大时,计算的相对误差较为准确,但高层激光雷达信噪比较小时,无法计算出相对误差。背景信号方法计算水汽混合比的相对误差时,信噪比较强时计算的相对误差偏小,但可以很好地表现出激光雷达回波信号的衰减趋势。对比结果显示:激光雷达自身计算相对误差和对比误差一致性较好,说明了激光雷达自身计算相对误差的可靠性。上述分析结果对于提高激光雷达测量水汽混合比的准确性,以及激光雷达测量结果在气象预报中的应用起到很好的辅助作用。
[Abstract]:In the atmosphere, water vapor is an important meteorological element, which plays an important role in cloud physics and precipitation formation process, atmospheric chemical reaction process and energy cycle process. Because of the particularity of water vapor and its influence on life meaning, water vapor is widely concerned by people because it is different from other gases. As an optical active remote sensing method, lidar system has long detection range, high precision and high sensitivity. Therefore, the lidar system is widely used in the fields of atmospheric detection, environmental monitoring, climate research and so on. Based on the data collected by the self-developed Raman lidar system, the water vapor mixing ratio is calculated. According to the error transfer theory, each error source of water vapor mixing ratio error is analyzed item by item. The results show that the error of measuring water vapor mixing ratio by lidar mainly includes calibration constant. Atmospheric transmittance correction and echo signal are three error sources. The calibration constant error is closely related to system parameters and calibration methods, and does not change with height. About 4-6, which is the main source of the total relative error of water vapor mixing ratio measured by lidar less than 1.5 km. The correction error of atmospheric transmittance is mainly derived from the optical properties of the actual atmosphere and increases with the elevation. The effect on total relative error under clean weather condition is less than 4, and that on total relative error under polluted weather condition is less than 5. The echo signal error is related to system parameters and atmospheric characteristics. The echo signal error is generally less than 20 when the vertical height is less than 3 km, and above 3 km at the vertical altitude, which is the main source of the total relative error of the water vapor mixing ratio. The echo signal error is generally less than 30 km, and above 2 km, it is the main source of the total relative error of the water vapor mixing ratio. Because the relative error of the echo signal is the most uncertain part of the total water vapor mixing ratio error, In order to analyze the relative error of laser radar echo signal in detail, the whole error of water vapor mixing ratio is calculated by using random error method, Poisson formula method and background signal method, respectively. The contrast experiment between lidar and radiosonde is used to measure the water vapor mixing ratio. The three methods for calculating the relative error of echo signal are analyzed and verified. The results show that each of the three methods has its own advantages, disadvantages and applicable conditions. When the random error method is used to calculate the relative error of water vapor mixing ratio, When calculating the relative error of water vapor mixing ratio by Poisson formula method, when the signal-to-noise ratio of lidar is larger, the relative error is more accurate. However, the relative error can not be calculated when the signal-to-noise ratio of high level lidar is small. When the background signal method calculates the relative error of water vapor mixing ratio, the relative error is small when the signal-to-noise ratio is strong. However, the attenuation trend of laser radar echo signal can be well demonstrated. The comparison results show that the relative error and contrast error of the laser radar itself are in good agreement. The reliability of the relative error calculation of lidar itself is explained. The above results can improve the accuracy of lidar measurement of water vapor mixing ratio and the application of lidar measurement results in weather forecast.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P407.5

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