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.
