Three-Dimensional Near-Surface Turbulent Anisotropic Structure Function Measurements

A common assumption used in describing the turbulence structure present during atmospheric propagation is turbulent isotropy. Yet low frequency fluctuations obviously cannot exhibit this property since vertically oriented fluctuations are impacted by surface boundary conditions. To gain insight into the anisotropic nature of the surface boundary, a measurement campaign was carried out in the spring of 2008 at White Sands Missile Range, NM. A 2D array of 3D sonic anemometers was constructed. This array, a 14m wide by 10m high grid of sensors was used to sample wind and temperature fluctuations over a two-month period. More than 300 hours of data were collected that fit the criteria of sensor availability, mean winds directed from a desired sector, and steady wind speed. This paper describes the grid, the overall experiment, and considers aspects of correlations present in the temperature data fields that may be useful in characterizing an anisotropic refractive index structure function.