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A helicopter observation platform for atmospheric boundary layer studies.

机译：用于大气边界层研究的直升机观测平台。

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摘要

Spatial variability of the Earth's surface has a considerable impact on the atmosphere at all scales and understanding the mechanisms involved in land-atmosphere interactions is hindered by the scarcity of appropriate observations. A measurement gap exists between traditional point sensors and large aircraft and satellite-based sensors in collecting measurements of atmospheric quantities. Point sensors are capable of making long time series of measurements, but cannot make measurements of spatial variability. Large aircraft and satellites make measurements over large spatial areas, but with poor spatial and temporal resolution. A helicopter-based platform can make measurements on scales relevant for towers, especially close to the Earth's surface, and can extend these measurements to account for spatial variability. Thus, the Duke University Helicopter Observation Platform (HOP) is designed to fill the existing measurement gap.;Because measurements must be made in such a way that they are as uncontaminated by the platform itself as much as is possible, it is necessary to quantify the aerodynamic envelope of the HOP. The results of an analytical analysis of the location of the main rotor wake at various airspeeds are shown. Similarly, the results of a numerical analysis using the commercial Computational Fluid Dynamics software Fluent are shown. The optimal flight speed for the sampling of turbulent fluxes is found to be around 30 m/s. At this airspeed, the sensors located in front of the nose of the HOP are in advance of the wake generated by the main rotor. This airspeed is also low enough that the region of high pressure due to the stagnation point on the nose of the HOP does not protrude far enough forward to affect the sensors. Measurements of differential pressures, variables and turbulent fluxes made while flying the HOP at different airspeeds support these results. No systematic effects of the platform are seen at airspeeds above about 10 m/s.;Processing of HOP data collected using the current set of sensors is discussed, including the novel use of the Empirical Mode Decomposition (EMD) to detrend and filter the data. The EMD separates the data into a finite number of Intrinsic Mode Functions (IMFs), each of which is unique and orthogonal. The basis is determined by the data itself, so that it need not be known a priori, and it is adaptive. The EMD is shown to be an ideal tool for the filtering and detrending of the HOP data gathered during the Cloud and Land Surface Interaction Campaign (CLASIC).;The ability of the HOP to accurately measure atmospheric profiles of atmospheric variables is demonstrated. During experiments conducted in the marine boundary layer (MBL) and the convective boundary layer (CBL), HOP profiles of potential temperature are evaluated using an elastic backscatter lidar. The HOP and the lidar agree on the height of the boundary layer in both cases, and the HOP effectively locates other atmospheric structures.;Atmospheric sensible and latent heat fluxes, turbulence kinetic energy (TKE) and horizontal momentum fluxes are also measured, and the resulting information is used to provide context to tower-based data collected concurrently. A brief comparison made over homogeneous ocean conditions yields good results. A more exhaustive evaluation is made using short HOP flights performed above an orchard during the Canopy Horizontal Turbulence Study (CHATS). Randomly selected one-minute sections of tower data are used to calculate fluxes to which the HOP fluxes can be more directly compared, with good results. Profiles of atmospheric fluxes are used to provide context to tower-based measurements.;In conclusion, the research conducted here demonstrates unambiguously that the HOP is a unique platform that fills an important gap in observation facilities for the atmospheric boundary layer. It is now available to the scientific community for performing research, which is likely to help bridging existing knowledge gaps in various aspects of Earth surface (continental and maritime) -- atmosphere interactions.
机译：地球表面的空间变异性在所有尺度上对大气都有相当大的影响，由于缺乏适当的观测资料，阻碍了对陆地与大气相互作用机制的理解。在收集大气量的测量值时，传统的点传感器与大型飞机和基于卫星的传感器之间存在测量差距。点传感器能够进行长时间的测量，但是无法进行空间变异性的测量。大型飞机和卫星可以在较大的空间区域进行测量，但是空间和时间分辨率较差。基于直升机的平台可以在与塔相关的比例上进行测量，尤其是靠近地球表面的比例，并且可以扩展这些测量以解决空间可变性。因此，杜克大学直升机观测平台（HOP）旨在填补现有的测量空白。;由于必须以尽可能不受平台本身污染的方式进行测量，因此有必要进行量化HOP的空气动力学包络线。显示了在不同空速下主旋翼尾流位置的分析分析结果。同样，显示了使用商业计算流体动力学软件Fluent进行数值分析的结果。采样湍流的最佳飞行速度约为30 m / s。在此空速下，位于HOP机头前部的传感器位于主旋翼产生的尾流之前。该空速也足够低，以至于由于HOP鼻部上的停滞点而导致的高压区域没有足够远地向前突出以影响传感器。对以不同空速飞行的HOP进行的压差，变量和湍流的测量结果支持了这些结果。在高于约10 m / s的空速下，没有看到平台的系统性影响；讨论了使用当前传感器集收集的HOP数据的处理，包括新颖地使用经验模态分解（EMD）去趋势化和过滤数据。 EMD将数据分为有限数量的本征函数（IMF），每个固有函数都是唯一的且正交的。该基础由数据本身确定，因此无需先验就可以知道，它是自适应的。 EMD被证明是过滤和去趋势化在云与陆表面相互作用运动（CLASIC）期间收集的HOP数据的理想工具。展示了HOP能够准确测量大气变量的大气剖面的能力。在海洋边界层（MBL）和对流边界层（CBL）中进行的实验过程中，使用弹性反向散射激光雷达评估了潜在温度的HOP轮廓。在这两种情况下，HOP和激光雷达都在边界层的高度上一致，并且HOP有效地定位了其他大气结构。;还测量了大气的感热通量和潜热通量，湍流动能（TKE）和水平动量通量，并且结果信息用于为同时收集的基于塔的数据提供上下文。对均质海洋条件进行的简短比较得出了很好的结果。在冠层水平湍流研究（CHATS）期间，使用在果园上方进行的短程HOP飞行进行了更为详尽的评估。塔架数据的随机选择的一分钟部分用于计算磁通量，可以将HOP磁通量与之直接比较，从而获得良好的结果。大气通量剖面可用来为基于塔的测量提供背景信息。总之，在此进行的研究明确表明HOP是一个独特的平台，填补了大气边界层观测设施的重要空白。现在，科学界可以使用它进行研究，这很可能有助于弥合地球表面各个方面（大陆和海洋）与大气相互作用的现有知识空白。

著录项

  • 作者

    Holder, Heidi Eichinger.;

  • 作者单位

    Duke University.;

  • 授予单位 Duke University.;
  • 学科 Atmospheric Sciences.;Environmental Sciences.;Engineering Environmental.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 131 p.
  • 总页数 131
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 环境科学基础理论;环境污染及其防治;
  • 关键词

  • 入库时间 2022-08-17 11:38:23

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