Comparative analysis of C n2 estimation methods for sonic anemometer data.

Area of Science:

• Atmospheric physics
• Optical engineering
• Turbulence research

Background:

• The refractive index structure parameter (Cn2) is crucial for understanding optical propagation through the atmosphere.
• Ultrasonic anemometers measuring wind speed and sonic temperature are commonly used to estimate Cn2.
• Accurate Cn2 estimation is vital for applications in adaptive optics, remote sensing, and secure communications.

Purpose of the Study:

• To compare the performance of four distinct methods for estimating Cn2 from sonic temperature data.
• To evaluate the accuracy of these methods under varying atmospheric turbulence conditions.
• To determine appropriate error bars for Cn2 estimations based on temperature fluctuations.

Main Methods:

• Utilized temporal sonic temperature data from two separated ultrasonic anemometers on a homogenous path.
• Compared four estimation methods: Bayesian, power spectral, nearest neighbors, and structure function.
• Validated results against a commercial scintillometer and the differential image motion method.

Main Results:

• The Bayesian and power spectral methods provided adequate estimates for strong turbulence but overestimated Cn2 in weak turbulence.
• The nearest neighbors and structure function methods demonstrated robust performance across all tested turbulence strengths.
• Error bars for Cn2 were considered, accounting for finite turbulent sample sizes.

Conclusions:

• The nearest neighbors and structure function methods are recommended for reliable Cn2 estimation from sonic temperature data.
• The choice of method significantly impacts Cn2 accuracy, particularly under weak turbulence conditions.
• Further research into error quantification for Cn2 estimation is warranted.