Measurement and Calibration of Plant-Height from Fixed-Wing UAV Images.

Xiongzhe Han,Dale A Cope,Sorin C Popescu,G Cody Bagnall,N Ace Pugh,Anjin Chang,J Alex Thomasson,William L Rooney,David W Horne,Lonesome Malambo,Jinha Jung,Ian T Gates

doi:10.3390/s18124092

Xiongzhe Han, Dale A Cope + Show 10 more

Open Access

https://doi.org/10.3390/s18124092

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Abstract

Continuing population growth will result in increasing global demand for food and fiber for the foreseeable future. During the growing season, variability in the height of crops provides important information on plant health, growth, and response to environmental effects. This paper indicates the feasibility of using structure from motion (SfM) on images collected from 120 m above ground level (AGL) with a fixed-wing unmanned aerial vehicle (UAV) to estimate sorghum plant height with reasonable accuracy on a relatively large farm field. Correlations between UAV-based estimates and ground truth were strong on all dates (R2 > 0.80) but are clearly better on some dates than others. Furthermore, a new method for improving UAV-based plant height estimates with multi-level ground control points (GCPs) was found to lower the root mean square error (RMSE) by about 20%. These results indicate that GCP-based height calibration has a potential for future application where accuracy is particularly important. Lastly, the image blur appeared to have a significant impact on the accuracy of plant height estimation. A strong correlation (R2 = 0.85) was observed between image quality and plant height RMSE and the influence of wind was a challenge in obtaining high-quality plant height data. A strong relationship (R2 = 0.99) existed between wind speed and image blurriness.

Highlights

Continuing population growth will result in increasing global demand for food and fiber for the foreseeable future
It is clear that fixed-wing unmanned aerial vehicle (UAV) at 120 m above ground level (AGL) have the potential to estimate plant height, which enables measurements to be made over relatively larger fields that could not be covered with standard hand based methods and might be too large for rotary-wing
Results of this study indicate that fixed-wing UAV images collected at 120 m AGL can be used to estimate sorghum plant height and growth trends reasonably well and multi-level ground control points (GCPs) are helpful in reducing error on relatively flat terrain

Summary

Introduction

Continuing population growth will result in increasing global demand for food and fiber for the foreseeable future. Sensors 2018, 18, 4092 meet world agricultural productions such as crop improvement through plant breeding and genetics and production optimization through precision-agriculture management strategies [3,4] In both cases, the measurement of numerous traits such as plant height, leaf-area cover, and crop density is essential for increasing yield potential and protection from crop losses. Vegetation indices from these sensors can potentially be used for making decisions and performing actions in farm management [23,24] Since they can collect multiple images over the same area during a flight, UAVs can help determine plant height, which is useful in assessing the influence of environmental conditions on plant performance and is an important phenotype for crop improvement and production optimization

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