Optical Tomography of the Atmospheric Surface Layer

由于主要的交换过程控制着局地、区域和全球尺度的天气和气候，大气表层（ASL）是大气最重要的部分之一。虽然ASL可以很容易地进行点测量，但高精度和高精度的线平均和面平均微气象变量（如热量和动量通量）的量化仍然是一个重大的科学和技术挑战。这项工作的中心目标是加强、完善和应用大气表层光学层析成像的科学和技术，重点是利用光谱可见部分水平传播光的无处不在的垂直和水平到达角（AOA）波动。这种AOA波动携带有关横向风速分量和横向温度梯度分量沿传播路径的平均值和波动的信息，将由一个或两个配备CCD相机的大口径望远镜观测视场中的一系列测试灯。单台望远镜可反演的微气象观测资料主要有：(1)瞬时温度梯度、路径平均温度梯度、水平温度梯度和垂直温度梯度的时间波动；(2)路径横向风速水平分量和垂直分量的路径平均值；(3)温度湍流结构参数的路径平均。一对横向间隔望远镜将进行距离分辨观测。还将探讨检索其他湍流统计数据的可能性，例如垂直和水平速度分量的方差以及热量和动量的垂直和横向通量。光学反演量将与沿传播路径的独立原位测量进行比较，以便定性和定量地检验潜在的假设。本课题的智力优势在于利用光学AOA波动测量和现场风速、温度测量相结合的方法获取和分析大气表层风场和温度场的时空特征，从而进一步了解大气表层风场和温度场的时空特征。基于几何光学和马尔可夫近似以及局部均匀和各向同性湍流假设的光学AOA层析成像的优势和局限性将通过Rytov理论进行理论探讨，并通过将光学检索的观测结果与配置的原位测量结果进行比较来进行经验研究，以补充现有的ASL遥感技术，如激光雷达、闪烁测量和声学层析成像。这一努力的广泛影响将通过研究生教育和探索更经济、更方便、更敏感的探查美国手语的方法而产生。改进大气光透射特性和衍生通量量，为微气象学、水文学、可再生能源和气候物理学的研究和业务目标提供了成熟的更强大的标准技术的潜力。

Owing to predominant exchange processes that govern weather and climate on local, regional, and global scales, the atmospheric surface layer (ASL) is one of the most important parts of the atmosphere. While the ASL is easily accessible to point measurements, quantifying with high precision and accuracy line- and areal-averages micrometeorological variables such as heat and momentum flux remains a major scientific and technological challenge. A central goal of this effort is to enhance, refine and apply the science and technology of optical tomography of the atmospheric surface layer, where we focus on exploiting the ubiquitous vertical and horizontal angle-of-arrival (AOA) fluctuations of horizontally propagating light in the visible part of the spectrum. Such AOA fluctuations, which carry information about mean values and fluctuations of the transverse wind velocity components and of the transverse temperature gradient components along the propagation path, will be observed with one or two large-aperture telescopes equipped with CCD cameras observing an array of test lights in the field(s) of view. The three primary micrometeorological observables that can be retrieved with a single telescope are (1) temporal fluctuations of instantaneous, path-averaged, horizontal and vertical temperature gradients; (2) path averages of the horizontal and vertical components of the path-transverse wind velocity; and (3) path averages of the temperature turbulence structure parameter. A pair of laterally spaced telescopes will lead to range-resolved observations. The possibility to retrieve other turbulence statistics, such as variances of vertical and horizontal velocity components as well as vertical and lateral fluxes of heat and momentum, will also be explored. Optically retrieved quantities will be compared with independent in-situ measurements along the propagation path in order to test the underlying hypotheses qualitatively and quantitatively.The intellectual merit of this research program is centered on means to obtain and perform combined analysis of optical AOA fluctuation measurements and in-situ wind velocity and temperature measurements so as to obtain lead to a deeper understanding of the spatiotemporal characteristics of the wind and temperature fields in the atmospheric surface layer. Both strengths and limitations of optical AOA tomography based on the geometrical-optics and Markov approximations and the assumption of locally homogeneous and isotropic turbulence will be explored theoretically by means of the Rytov theory and empirically by means of comparing optically-retrieved observables with collocated in-situ measurements so as to complement existing ASL remote sensing techniques, such as lidar, scintillometry, and acoustic tomography. Broader impacts of this effort will be derived through graduate student education and exploration of more economical, readily portable and perhaps more sensitive means of probing the ASL. Improved characterization of atmospheric light transmission and derived flux quantities offer the potential to mature into a more powerful standard technology for both research and operational objectives in micrometeorology, hydrology, renewable energy and climate physics.