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Spectral correction of turbulent energy damping on wind lidar measurements due to spatial averaging
Atmospheric Measurement Techniques ( IF 3.2 ) Pub Date : 2021-02-24 , DOI: 10.5194/amt-14-1457-2021
Matteo Puccioni , Giacomo Valerio Iungo

Continuous advancements in pulsed wind lidar technology have enabled compelling wind turbulence measurements within the atmospheric boundary layer with probe lengths shorter than 20 m and sampling frequency on the order of 10 Hz. However, estimates of the radial velocity from the back-scattered lidar signal are inevitably affected by an averaging process within each probe volume, generally modeled as a convolution between the true velocity projected along the lidar line-of-sight and an unknown weighting function representing the energy distribution of the laser pulse along the probe length. As a result, the spectral energy of the turbulent velocity fluctuations is damped within the inertial subrange, thus not allowing one to take advantage of the achieved spatio-temporal resolution of the lidar technology. We propose to correct the turbulent energy damping on the lidar measurements by reversing the effect of a low-pass filter, which can be estimated directly from the power spectral density of the along-beam velocity component. Lidar data acquired from three different field campaigns are analyzed to describe the proposed technique, investigate the variability of the filter parameters and, for one dataset, assess the corrected velocity variance against sonic anemometer data. It is found that the order of the low-pass filter used for modeling the energy damping on the lidar velocity measurements has negligible effects on the correction of the second-order statistics of the wind velocity. In contrast, the cutoff wavenumber plays a significant role in spectral correction encompassing the smoothing effects connected with the lidar probe length. Furthermore, the variability of the spatial averaging on wind lidar measurements is investigated for different wind speed, turbulence intensity, and sampling height. The results confirm that the effects of spatial averaging are enhanced with decreasing wind speed, smaller integral length scale and, thus, for smaller sampling height. The method proposed for the correction of the second-order turbulent statistics of wind-velocity lidar data is a compelling alternative to existing methods because it does not require any input related to the technical specifications of the used lidar system, such as the energy distribution over the laser pulse and lidar probe length. On the other hand, the proposed method assumes that surface-layer similarity holds.

中文翻译:

空间平均对风激光雷达测量中湍流能量阻尼的频谱校正

脉冲风激光雷达技术的不断发展已使大气边界层内的风湍流测量引人注目,探头长度短于20 m,采样频率约为10 Hz。但是,来自反向散射激光雷达信号的径向速度的估计不可避免地会受到每个探头体积内平均过程的影响,通常将其建模为沿激光雷达视线投影的真实速度与未知加权函数之间的卷积沿探针长度的激光脉冲能量分布。结果,湍流速度波动的频谱能量在惯性子范围内被衰减,从而使人们无法利用激光雷达技术的时空分辨率。我们建议通过反转低通滤波器的影响来校正激光雷达测量结果中的湍流能量阻尼,该低通滤波器可以直接从沿光束速度分量的功率谱密度估算得出。分析了从三个不同的野战中获取的激光雷达数据,以描述所提出的技术,研究过滤器参数的可变性,并针对一个数据集,评估针对声速风速计数据的校正速度方差。发现在激光雷达速度测量中用于对能量衰减建模的低通滤波器的阶数对风速二阶统计量的校正影响可忽略不计。相反,截止波数在频谱校正中起着重要作用,涵盖了与激光雷达探头长度有关的平滑效果。此外,针对不同的风速,湍流强度和采样高度,研究了在风激光雷达测量中空间平均的可变性。结果证实,空间平均的效果随着风速的降低,整体长度尺度的减小以及采样高度的减小而增强。提议的用于校正风速激光雷达数据的二阶湍流统计量的方法是现有方法的一种引人注目的替代方法,因为它不需要与所用激光雷达系统的技术规格相关的任何输入,例如在激光脉冲和激光雷达探头的长度。另一方面,提出的方法假定表面层相似性成立。针对不同的风速,湍流强度和采样高度,研究了风平均在激光雷达测量中的变异性。结果证实,空间平均的效果随着风速的降低,整体长度尺度的减小以及采样高度的减小而增强。提议的用于校正风速激光雷达数据的二阶湍流统计量的方法是现有方法的一种引人注目的替代方法,因为它不需要与所用激光雷达系统的技术规范相关的任何输入,例如在激光脉冲和激光雷达探头的长度。另一方面,提出的方法假定表面层相似性成立。针对不同的风速,湍流强度和采样高度,研究了风激光雷达测量的空间平均变异性。结果证实,空间平均的效果随着风速的降低,整体长度尺度的减小以及采样高度的减小而增强。提议的用于校正风速激光雷达数据的二阶湍流统计量的方法是现有方法的一种引人注目的替代方法,因为它不需要与所用激光雷达系统的技术规范相关的任何输入,例如在激光脉冲和激光雷达探头的长度。另一方面,提出的方法假定表面层相似性成立。结果证实,空间平均的效果随着风速的降低,整体长度尺度的减小以及采样高度的减小而增强。提议的用于校正风速激光雷达数据的二阶湍流统计量的方法是现有方法的一种引人注目的替代方法,因为它不需要与所用激光雷达系统的技术规范相关的任何输入,例如在激光脉冲和激光雷达探头的长度。另一方面,提出的方法假定表面层相似性成立。结果证实,空间平均的效果随着风速的降低,整体长度尺度的减小以及采样高度的减小而增强。提议的用于校正风速激光雷达数据的二阶湍流统计量的方法是现有方法的一种引人注目的替代方法,因为它不需要与所用激光雷达系统的技术规格相关的任何输入,例如在激光脉冲和激光雷达探头的长度。另一方面,提出的方法假定表面层相似性成立。提议的用于校正风速激光雷达数据的二阶湍流统计量的方法是现有方法的一种引人注目的替代方法,因为它不需要与所用激光雷达系统的技术规格相关的任何输入,例如在激光脉冲和激光雷达探头的长度。另一方面,提出的方法假定表面层相似性成立。提议的用于校正风速激光雷达数据的二阶湍流统计量的方法是现有方法的一种引人注目的替代方法,因为它不需要与所用激光雷达系统的技术规范相关的任何输入,例如在激光脉冲和激光雷达探头的长度。另一方面,提出的方法假定表面层相似性成立。
更新日期:2021-02-24
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