Comparative analysis of 𝐂 𝟐 𝐧 estimation methods for sonic anemometer data

• Melissa Beason, Guy Potvin, Detlev Sprung, Jack McCrae, and Szymon Gladysz
• received 02/04/2024; accepted 04/12/2024; posted 04/19/2024; Doc. ID 520976
• Abstract: Wind speed and sonic temperature measured with ultrasonic anemometers are oftenutilized to estimate the refractive index structure parameter 𝐶2𝑛, a vital parameter for opticalpropagation. In this work, we compare four methods to estimate 𝐶2𝑛 from 𝐶2𝑇 using the sametemporal sonic temperature data streams for two separated sonic anemometers on ahomogenous path. Values of 𝐶2𝑛 obtained with these four methods using field trial data arecompared to those from a commercial scintillometer and from the differential image motionmethod using a grid of light sources positioned at the end of a common path. In addition to thecomparison between the methods, we also consider appropriate error bars for 𝐶2𝑛 based on sonictemperature considering only the errors from having a finite number of turbulent samples. TheBayesian and power spectral methods were found to give adequate estimates for strongturbulence levels, but consistently overestimated the 𝐶2𝑛 for weak turbulence. The nearestneighbors and structure function methods performed well under all turbulence strengths tested.