Comparative analysis of <i>C</i> <i>n</i>2 estimation methods for sonic anemometer data
Melissa Beason, Guy Potvin, Detlev Sprung, Jack E. McCrae, Szymon Gładysz
Abstract
Wind speed and sonic temperature measured with ultrasonic anemometers are often utilized to estimate the refractive index structure parameter C n 2 , a vital parameter for optical propagation. In this work, we compare four methods to estimate C n 2 from C T 2 , using the same temporal sonic temperature data streams for two separated sonic anemometers on a homogenous path. Values of C n 2 obtained with these four methods using field trial data are compared to those from a commercial scintillometer and from the differential image motion method using a grid of light sources positioned at the end of a common path. In addition to the comparison between the methods, we also consider appropriate error bars for C n 2 based on sonic temperature considering only the errors from having a finite number of turbulent samples. The Bayesian and power spectral methods were found to give adequate estimates for strong turbulence levels but consistently overestimated the C n 2 for weak turbulence. The nearest neighbors and structure function methods performed well under all turbulence strengths tested.