Robust Solution for Boundary Layer Height Detections with Coherent Doppler Wind Lidar

Abstract

Although coherent Doppler wind lidar (CDWL) is promising in detecting boundary layer height (BLH), differences between BLH results are observed when different CDWL measurements are used as tracers. Here, a robust solution for BLH detections with CDWL is proposed and demonstrated: mixed layer height (MLH) is retrieved best from turbulent kinetic energy dissipation rate (TKEDR), while stable boundary layer height (SBLH) and residual layer height (RLH) can be retrieved from carrier-to-noise ratio (CNR). To study the cause of the BLH differences, an intercomparison experiment is designed with two identical CDWLs, where only one is equipped with a stability control subsystem. During the experiment, it is found that the CNR could be distorted by instrument instability because the coupling efficiency from free-space to the polarization-maintaining fiber of the telescope is sensitive to the surrounding environment. In the ML, a bias up to 2.13 km of the MLH from CNR is found, which is caused by the CNR deviation. In contrast, the MLH from TKEDR is robust as long as the accuracy of wind is guaranteed. In the SBL (RL), the CNR is found capable to retrieve SBLH and RLH simultaneously and robustly. This solution is tested during an observation period over one month. Statistical analysis shows that the root-mean-square errors (RMSE) in the MLH, SBLH, and RLH are 0.28 km, 0.23 km, and 0.24 km, respectively.

摘 要

尽管相干多普勒测风激光雷达在边界层高度探测方面有很好的应用前景, 但当采用不同的观测数据时, 边界层高度的探测结果存在差异. 本文提出了一种基于相干多普勒测风激光雷达探测边界层高度的稳健方法: 用湍流动能耗散率确定混合层高度, 用载噪比确定稳定边界层高度和残留层高度. 为了研究边界层探测高度差异的成因, 本文采用了两台相同机制的雷达作对比, 并为其中一台配备了温控装置. 实验发现, 由于自由空间到望远镜保偏光纤的耦合效率对环境敏感, 仪器不稳定性将导致载噪比误差, 进而导致基于载噪比确定的混合层高度出现高达 2.13km 的偏移. 相比之下, 只要风场观测数据是准确的, 基于湍流动能耗散率就可以稳健地确定混合层高度. 实验还发现载噪比可以稳健地确定稳定边界层高度和残留层高度. 为了验证该方法的有效性, 本文进行了为期一个月的实验, 统计结果表明: 混合层高度, 稳定边界层高度和残留层高度的均方根误差分别为 0.28km, 0.23km 和 0.24km.