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ARS Home » Pacific West Area » Maricopa, Arizona » U.S. Arid Land Agricultural Research Center » Water Management and Conservation Research » Research » Publications at this Location » Publication #384447
Research Project: Advancing Water Management and Conservation in Irrigated Arid Lands

Location: Water Management and Conservation Research

Title: Comparison of image georeferencing strategies for agricultural applications of small unoccupied aircraft systems

Author
item PUGH, N - University Of Arizona
item Thorp, Kelly
item GONZALEZ, EMMANUEL - University Of Arizona
item ELSHIKHA, DIAA - University Of Arizona
item PAULI, DUKE - University Of Arizona

Submitted to: The Plant Phenome Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2021
Publication Date: 11/2/2021
Citation: Pugh, N.A., Thorp, K.R., Gonzalez, E.M., Elshikha, D.E., Pauli, D. 2021. Comparison of image georeferencing strategies for agricultural applications of small unoccupied aircraft systems. The Plant Phenome Journal. 4(1). Article e20026. https://doi.org/10.1002/ppj2.20026.
DOI: https://doi.org/10.1002/ppj2.20026

Interpretive Summary: Small unoccupied aircraft systems (sUAS or "drones") are rapidly becoming popular tools for imaging agricultural fields and quantifying crop characteristics. A persistent problem for use of information from drones is the accuracy of assigning spatial geographic coordinates to the image pixels, a process known as georeferencing. In this study, various methods, including different drones, field sizes, number and arrangement of known coordinates, and processing software, were compared to identify scenarios leading to improved georeferencing accuracy of drone-based images. The results demonstrated that four known coordinates at the field corners or use of real-time kinematic (RTK) positioning equipment were sufficient for optimizing georeferencing accuracy. Results are useful for researchers and practitioners in a variety of scientific disciplines, who aim to use drones for Earth surface mapping applications.

Technical Abstract: Small unoccupied aircraft systems (sUAS) are becoming popular for mapping applications in agriculture, and photogrammetry software is available for developing orthorectified imagery and three-dimensional surface models. Ground control points (GCPs), which are objects or locations with known geographic coordinates, may be required for accurate image georeferencing. However, few studies have compared global position equipment among sUAS or investigated the effects of GCP number or arrangement on georeferencing accuracy. The objectives of this study were to evaluate numbers and configurations of GCPs for georeferencing sUAS-acquired images and determine the GCP requirements for sUAS with and without real-time kinematic (RTK) global positioning equipment. The effects of varying numbers and configurations of GCPs were investigated on both a 0.40-ha area the size of a typical plant breeding trial and a 64.7-ha area (i.e., a U.S. quarter section) the size of a typical agricultural production field. Results demonstrated that four GCPs placed at the corners of the breeding-scale field resulted in two-dimensional (2D) error of ±3 cm in the absence of RTK, with minimal improvements when including more GCPs. The orthomosaics from the RTK-equipped sUAS demonstrated improved 2D accuracy even without the use of GCPs, with a maximum mean error of 0.08 m. Four GCPs were found to be sufficient to reduce altitudinal (Z) error, with maximum mean error of only 0.05 and 1.98 m for the RTK and non-RTK flights, respectively, for the production-scale field. Thus, using four GCPs, RTK-equipped sUAS, or a combination will result in improved georeferencing for photogrammetry products.