THREE-DIMENSIONAL WIND SPEED AND FLUX MEASUREMENTS OVER A RAIN-FED SOYBEAN FIELD USING ORTHOGONAL AND NON-ORTHOGONAL SONIC ANEMOMETER DESIGNS

Authors

Taylor Thomas, University of Nebraska‐LincolnFollow

Date of this Version

Fall 12-10-2015

Citation

Thomas, T. (2015) Three-Dimensional Wind Speed and Flux Measurements over a Rain-fed Soybean Field Using Orthogonal and Non-orthogonal Sonic Anemometer Designs. Thesis. University of Nebraska - Lincoln.

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Natural Resource Sciences, Under the Supervision of Professor Andrew E. Suyker. Lincoln, Nebraska: December, 2015

Copyright (c) 2015 Taylor M. Thomas

Abstract

The eddy covariance method for estimating fluxes of trace gases, energy and momentum in the constant flux layer above a plant canopy fundamentally relies on accurate measurements of the vertical wind speed. This wind speed is typically measured using a three-dimensional ultrasonic anemometer. Previous studies comparing anemometers with orthogonal transducer sets to those with non-orthogonal transducer sets suggest differences in measured 3D wind speed components, particularly for a vertical component. These differences, attributed to additional flow distortion caused by the non-orthogonal transducer arrangement and support structure, directly affect fluxes of trace gases, energy and momentum. A field experiment was conducted over a rain-fed soybean field at the AmeriFlux site (US-Ne3) near Mead, Nebraska to quantify these differences. Ultrasonic anemometers featuring orthogonal transducer sets (ATI Vx Probe) and non-orthogonal transducer sets (Gill R3) collected high frequency wind vector and sonic temperature data. The non-orthogonal Gill R3 models underestimated sensible heat flux by 11% and friction velocity by 5% relative to the ATI Vx orthogonal design under the same atmospheric conditions. For two versions of an angle of attack correction developed for this non-orthogonal anemometer, neither adequately corrected the Gill R3 sensible heat fluxes compared to those measured using the orthogonal ATI Vx probe.

Adviser: Dr. Andrew E. Suyker