Using ultrasonic anemometers for temperature measurements and implications on Cn2
High frequency fluctuations in the refractive index are the main atmospheric influence on wave propagation in the atmosphere. They are caused mainly from variations in atmospheric temperature. Ultrasonic anemometers have been established as common tools in performing in-situ measurements of turbulence. They were used as fixed point instruments from towers, for the characterization of local turbulence or from mobile platforms. Besides wind velocity fluctuations, high frequency variations of the sonic temperature are analyzed. Time series of temperature data are analyzed to derive the structure function of temperature CT 2, that should be proportional the strength of optical turbulence Cn 2. The application of the Fast Fourier transformation, temporal resolution and averaging time are addressed to show the applicability of ultrasonic anemometers. Also the influence of humidity fluctuations on the determination of Cn 2 in applications over land and over the sea is discussed. Errors in the applications from fixed points as well as from mobile platforms are estimated for different types of anemometers.
Eijk, Alexander M.J. van