Optical Tomography of the Atmospheric Surface Layer

由于在地方、区域和全球尺度上控制天气和气候的主要交换过程，大气近地层（ASL）是大气的最重要部分之一。 虽然ASL很容易进行点测量，但以高精度和准确度量化线平均和区域平均微气象变量，如热量和动量通量，仍然是一个重大的科学和技术挑战。 这项工作的一个中心目标是加强，完善和应用大气表面层光学层析成像的科学和技术，在那里我们专注于利用无处不在的垂直和水平到达角（AOA）波动的水平传播光在可见光谱的一部分。 这种AOA波动携带着关于沿着传播路径的横向风速分量和横向温度梯度分量的平均值和波动的信息，将用一个或两个配备有CCD摄像机的大孔径望远镜观测视场中的测试光阵列。 可以用一台望远镜反演的三个主要微气象观测量是：（1）瞬时、路径平均、水平和垂直温度梯度的时间波动;（2）路径横向风速的水平和垂直分量的路径平均;（3）温度湍流结构参数的路径平均。 一对横向间隔的望远镜将导致距离分辨观测。 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。 为了定性和定量地检验基本假设，光学反演的量将与沿传播路径沿着的独立原位测量值进行比较。现场风速和温度测量，以获得导致更深入地了解风场和温度场的时空特征，大气表层 光学AOA层析成像的优势和局限性的基础上的几何光学和马尔可夫近似和假设的局部均匀和各向同性的湍流将探索理论上的Rytov理论和经验的比较光学检索的观测量与同位的原位测量，以补充现有的ASL遥感技术，如激光雷达，测距，和声学层析成像。 通过研究生教育和探索更经济、更容易携带、也许更敏感的探测ASL的方法，将产生更广泛的影响。 改进大气光透射特性和导出的通量量，有可能使其成熟为更强大的标准技术，用于微气象学、水文学、可再生能源和气候物理学的研究和业务目标。

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.