基于激光云高仪反演全天边界层高度的两步曲线拟合法

大气边界层高度是天气、气候、大气环境研究中的一个重要参数，目前尚缺少基于激光雷达探测系统反演全天边界层高度的有效方法。文中利用北京朝阳站、大兴站的激光云高仪数据，首先评估了梯度法、标准偏差法、曲线拟合法和小波协方差法反演边界层高度的适用性和局限性，发现梯度法容易受环境噪声的影响，曲线拟合法稳定性较好，但在夜间弱湍流条件下会将残留层高度误判为夜间边界层高度。提出两步曲线拟合法，将一天中边界层结构划分为白天的对流边界层、夜间的残留层和稳定边界层，通过用不同的理想曲线对其进行两步拟合，获取全天边界层高度的变化。将两步曲线拟合法的反演结果与基于L波段探空雷达的位温梯度法的探测结果进行比较发现:两者相关系数为0.91，证明了两步曲线拟合法的可行性以及激光云高仪探测边界层高度的应用潜力。采用该方法反演2017年5—6月朝阳站与大兴站边界层高度，对比发现:城区特殊的下垫面性质使朝阳站日间对流边界层发展更早，边界层高度更高，全天朝阳站边界层高度的变化在308—1391 m，大兴站在197—1302 m。 

A two-step ideal curve fitting method for retrieving full-day planetary boundary layer height based on ceilometer data

Planetary boundary layer height (PBLH) is an important parameter in the study of weather, climate and atmospheric environment. However, there is no effective method to retrieve PBLH of the whole day based on lidar system. In this paper, the applicability and limitation of the Gradient method (GRD), the Standard Deviation method (STD), the Ideal Curve Fitting method (ICF) and the Wavelet Covariance Transform method (WCT) for the retrieval of PBLH are evaluated by using ceilometer data collected at Chaoyang and Daxing stations in Beijing. It is found that the GRD is susceptible to environmental noises and the ICF has preferable stability, but the latter would mistake residual layer height for PBLH in the nighttime when turbulence is weak. On this basis, this paper establishes a Two-step Ideal Curve Fitting method (2-S ICF), which divides the structure of planetary boundary layer into convective boundary layer in the daytime, and residual layer and stable boundary layer in the nighttime. Through two-step fitting with different ideal curves, the full-day PBLH can be obtained. The retrievals of 2-S ICF are compared with those obtained by the potential temperature gradient method based on L-band sounding radar. The results show that the correlation coefficient of results by the two methods is 0.91, which verifies the feasibility of the 2-S ICF and the application potential of the ceilometer in detecting PBLH. PBLHs at Chaoyang Station and Daxing Station from May to June 2017 are retrieved by using this method. It is found that convective boundary layer develops more rapidly in the daytime and the PBLH is higher at Chaoyang Station because of the influence of the special surface characteristics in urban area. The PBLH ranges are 308—1391 m and 197—1302 m throughout the day at Chaoyang station and Daxing station, respectively.