Date Available

11-19-2025

Year of Publication

2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Engineering

Department/School/Program

Mechanical Engineering

Faculty

Dr. Sean Bailey

Faculty

Dr. Jonathan Wenk

Abstract

This study explores the use of a balloon-launched uncrewed aircraft system (UAS) to measure atmospheric turbulence in the troposphere and lower stratosphere using both wind velocity measurements and infrasonic acoustic energy. The UAS, a glider configured for autonomous descent along a predefined trajectory, had on board, in situ sensors to capture thermodynamic and kinematic atmospheric parameters. Additionally, it carried an infrasonic microphone to evaluate its potential for remotely detecting clear-air turbulence by capturing infrasonic waves. The system’s performance was assessed over the course of three test flights conducted in New Mexico, USA, in 2021. The descent enabled high-resolution profiling, with typical vertical resolutions of approximately 1 m for temperature, relative humidity, and pressure, and around 0.1 m for the wind velocity vector. Analytical methods were developed to estimate turbulent kinetic energy and dissipation rate; however, the Richardson number exhibited sensitivity to the chosen method for computing vertical gradients from single-flight data. A comparison between EDR and Richardson number showed that there is a general agreement between increased turbulent kinetic energy for Ri < 1, but there are still multiple regions that show high Ri with increased turbulent kinetic energy. Thorpe scale analysis was also applied to vertical potential temperature profiles to estimate overturning scales associated with turbulent mixing. The calculated Thorpe displacements were used to derive Thorpe length scales, providing an independent estimate of turbulence intensity and structure. These results were compared with dissipation rates derived from kinetic energy-based methods which showed some agreement, especially in the boundary layer. At high altitudes, the infrasonic microphone’s low-frequency signal content qualitatively corresponded to large-scale wind fluctuations. Furthermore, the microphone detected a broader frequency spectrum when the glider encountered turbulence originating from the boundary layer. In addition, a second study was done at lower altitudes to capture turbulence parameters changing during the morning as the convective boundary layer develops. This experiment includes the same set of sensors on a different UAS flying at an altitude of 100 m. A comparison of the variance of the infrasonic energy and the turbulent kinetic energy shows that an increase in turbulent kinetic energy corresponds to an increase in infrasonic energy as well which corresponds to the previous findings of high-altitude experiment.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.508

Funding Information

National Aeronautics and Space Administration under the Flight Opportunities Program through award number 80NSSC20K0102.

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