Author ORCID Identifier

https://orcid.org/0009-0000-3218-9168

Date Available

5-9-2023

Year of Publication

2023

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Agriculture; Engineering

Department/School/Program

Biosystems and Agricultural Engineering

Advisor

Dr. Michael P. Sama

Abstract

The overarching objective of this research was to enhance our comprehension of the three-dimensional precision of meteorological measurements obtained using small unmanned aircraft systems (UAS). Two complimentary experiments were conducted to achieve this objective.

The first experiment entailed the development and implementation of a system to determine the global navigation satellite system (GNSS) position accuracy on a UAS platform. This system was utilized to assess the static and dynamic accuracy of L1 and L1/L2 GNSS receivers in real-time kinematic (RTK) and non-RTK fix modes. Adjusted two-sample t-tests revealed significant differences in horizontal and vertical error between RTK and non-RTK receivers across the various deployment strategies. The findings indicate that RTK receivers produce more precise measurements with significantly fewer errors compared to non-RTK receivers. However, the practical significance of these differences warrants separate consideration. The study emphasizes the importance of using RTK receivers when conducting meteorological measurements, especially vertical profiles, and suggests the need for further research to differentiate the impact of treatments from the influence of external factors on receiver accuracy.

The second experiment involved the development of a set of miniature pressure, temperature, and relative humidity (PTH) probes for UAS integration. An automated calibration/validation routine was devised to calibrate the PTH probes using an environmental chamber. The results of the Tukey-Kramer procedures revealed that fewer calibrated sensors were statistically different from each other compared to uncalibrated sensors, reducing intersensory bias and demonstrating the value of calibrating different sensor models to a common reference. The linear regression offsets showed that calibration was necessary to meet the desired accuracy specification. In most UAS-based applications, the differences between the calibrated PTH probes were expected to be negligible, irrespective of their significance.

The outcomes of this research will enhance our ability to quantify minor variations in ambient conditions during coordinated multi-UAS flights. The low-cost GNSS receivers evaluated demonstrated centimeter-level accuracy under RTK mode, which eliminates the need to use barometric pressure sensors to correct for short-term drift in elevation from non-RTK GNSS measurements. The PTH probes demonstrated that research-grade meteorological measurements can be made using embedded sensors through careful design and calibration.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2023.214

Funding Information

This research was supported in part by the National Aeronautics and Space Administration (NASA) Kentucky Space Grant Consortium under NASA award number 80NSSC20M0047, the National Science Foundation (NSF) under award 1932105, and the United States Department of Agriculture National Institute of Food and Agriculture (USDA NIFA) Multistate Project S1069 under accession number 1539070.

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