基于CALIPSO星载激光雷达的边界层高度探测研究

发布时间：2019-06-12 12:27

【摘要】：气溶胶对人体健康、环境污染以及交通运输等产生着重要的影响。近年来大气污染问题比较突出。大气边界层作为与地表交互最为密切的大气,它与污染物进行着交互作用。因此,针对边界层的研究一直是国内外研究的一个热点问题,而边界层其中一个重要的特征即是边界层高度,也称为混合层高度,它是大气探测中的一个重要内容。但是传统的边界层高度测量方式空间覆盖度低,重复频率低或者精度低,针对这个不足,激光雷达作为主动的探测技术由于其全天时,高时间和垂直分辨率、能够连续探测大气等特点,发展成为一种有效的PBLH(Planetary boundary layer height)探测手段。除此之外,近十一年来,基于CALIPSO(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)星载激光雷达的PBLH探测也在逐渐的发展起来。相比于地基激光雷达,CALIPSO在空间覆盖上具有独特的优势。由于CALIPSO获取的信号信噪比低,本研究通过星载激光雷达的回波信号仿真分析,讨论了星载激光雷达系统参数对回波信号信噪比的影响,并通过改变累加脉冲,进行平滑效果分析。对CALIPSO的PBLH反演方法进行了探讨。目前,利用CALIPSO进行PBLH的反演时,主要采用的是最大方差法,但该方法本身存在PBLH误判的情况。此外,在面对不同的大气污染条件时,该方法还存在限制。最大方差法适用于清洁天气和部分卷云对流的情况,在边界层内有着高后向散射的混浊大气的情况,小波协方差方法则更为适用。本文对最大方差法通过增加判别条件的方式进行了改进,同时通过小波分析方法和最大方差法两者相结合的方式,发展了适用于不同大气气溶胶条件的综合PBLH探测算法,基于CALIPSO的观测,利用该算法反演得到中国区域的PBLH结果。选取六个典型地点,对中国典型区域的PBLH时序变化进行分析。通过中国区域的季节和年际变化分析,结果表明了PBLH在时间和空间上的分布特点。之后,利用ECMWF(European Center for Medium range Weather Forecasting)的再分析产品,对中国区域的PBLH进行了季节和年际变化分析,并与CALIPSO的相应结果进行了对比分析。论文主要的研究结论有:(1)利用地基激光雷达对北京站点上空的PBLH进行了探测,并进行不同污染状况下、多年日变化和多年季节变化的PBLH分析,结果显示PBLH在不同时间和大气污染状况下,呈现出一定的分布特点。(2)星载激光雷达的仿真分析表明,激光发射能量,接收口径大小,累加脉冲与信噪比成正相关,而滤波宽度,接收视场角大小和采样频率与信噪比成反相关。通过累加脉冲的平滑结果,表明回波信号的信噪比与平滑尺度成正相关,但随着平滑尺度的增大,回波信号的水平分辨率也在逐渐的降低。(3)利用地基激光雷达站点的观测,对CALIPSO获取的PBLH进行了验证。结果显示,对于Lille地基激光雷达站点,在无云的大气条件下,PBLH的平均绝对误差为206米,在悬浮层去掉后,平均误差为106米。对于Beijing地基激光雷达站点,它与CALIPSO的地面轨迹之间的平均距离超过40 km,PBLH的平均绝对误差为0.5 km。(4)基于CALIPSO的观测,利用综合的PBLH反演算法,获取了中国区域的PBLH。通过6个典型地点的PBLH的时序变化分析,反映了中国典型区域的大气污染状况。而中国区域的年变化和季节变化结果表明,PBLH具有明显的季节变化特征,春、夏季PBLH数值高,而秋、冬季数值低,PBLH的年际变化则不明显。通过对比ECMWF再分析资料获取的PBLH结果,发现两者之间差异较大。最后,利用由CALIPSO获取的PBLH对ECMWF的相应结果进行订正。
[Abstract]:The aerosol has an important influence on human health, environmental pollution and transportation. In recent year, that problem of air pollution is relatively prominent. The atmospheric boundary layer is the most closely related to the surface, and it interacts with the pollutants. Therefore, the study of the boundary layer has been a hot issue at home and abroad, and one of the most important features of the boundary layer is the height of the boundary layer, also known as the height of the mixed layer, which is an important part of the atmospheric sounding. but the traditional boundary layer height measuring method has the advantages of low space coverage, low repetition frequency or low precision, and aiming at the defect, the laser radar can continuously detect the atmosphere and the like due to the high time and the vertical resolution of the laser radar as the active detection technology, The development is an effective means of detection of the PBLH. In addition, the PBLH detection of the on-board laser radar based on the CALIPSO (Cloud-Aerosol Lidar and red Pathfinder Satellite Observation) has also been gradually developed for nearly a year. Compared with the ground lidar, the CALIPSO has a unique advantage over the space coverage. Since the signal-to-noise ratio of the signal obtained by CALIPSO is low, the influence of the parameters of the spaceborne laser radar system on the signal-to-noise ratio of the echo signal is discussed through the simulation and analysis of the echo signal of the satellite-borne laser radar, and the smoothing effect analysis is performed by changing the accumulated pulse. The PBLH inversion method for CALIPSO is discussed. At present, when using CALIPSO to carry out the inversion of the PBLH, the maximum variance method is mainly used, but the method itself is the case of the PBLH misjudgment. In addition, the method also has limitations in the face of different atmospheric conditions. The maximum variance method is suitable for the case of clean weather and partial volume cloud convection, and the wavelet covariance method is more applicable to the case of high-backward scattering of the turbid atmosphere in the boundary layer. In this paper, the method of maximum variance is improved by increasing the discrimination condition, and a comprehensive PBLH detection algorithm for different atmospheric aerosol conditions is developed by combining the wavelet analysis method and the maximum variance method, and based on the observation of CALIPSO, The result of PBLH in the Chinese region is obtained by using the algorithm. Six typical locations are selected for analysis of the PBLH timing changes in the typical region of China. Through the analysis of the seasonal and interannual variation of China's region, the distribution of PBLH in time and space is shown. Then, using the re-analysis of ECMWF (European Center for Medium range Weather Forecast), the seasonal and interannual change of PBLH in China's region was analyzed and compared with the corresponding results of CALIPSO. The main conclusions of this paper are as follows: (1) Using the ground lidar to detect the PBLH over the Beijing site, and to carry on the analysis of the PBLH with different pollution, for many years and for many years, the results show that the PBLH is under different time and air pollution. And has a certain distribution characteristic. (2) The simulation analysis of the satellite-borne laser radar shows that the laser emission energy, the size of the receiving aperture, the accumulation pulse and the signal-to-noise ratio are positively correlated, and the filter width, the receiving field angle size and the sampling frequency are inversely related to the signal-to-noise ratio. The result of the smoothing of the accumulated pulse indicates that the signal-to-noise ratio of the echo signal is positively correlated with the smoothing scale, but with the increase of the smooth scale, the horizontal resolution of the echo signal is gradually reduced. (3) The PBLH acquired by CALIPSO was verified by the observation of the ground laser radar site. The results show that for the Lille foundation laser radar site, the mean absolute error of PBLH is 206 m, and the average error is 106 m after the suspension layer is removed. For the Bejing foundation laser radar station, the average distance between it and the ground track of CALIPSO exceeds 40 km and the mean absolute error of PBLH is 0.5 km. (4) Based on the observation of CALIPSO, the PBLH in China is obtained by using the comprehensive PBLH inversion algorithm. The situation of atmospheric pollution in the typical region of China is reflected by the analysis of the time-series of the PBLH in six typical locations. The annual change and the seasonal change of the Chinese region show that the PBLH has obvious seasonal change characteristics, and the PBLH value in the spring and summer is high, and in autumn and winter, the interannual variation of the PBLH is not obvious. The results of the PBLH obtained by comparing the ECMWF re-analysis data revealed a large difference between the two. Finally, the corresponding results of ECMWF were revised using the PBLH obtained by CALIPSO.
【学位授予单位】：中国科学院大学(中国科学院遥感与数字地球研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X831

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