Study on extraction of apple tree height at different flight altitudes using multispectral UAV

doi:10.6048/j.issn.1001-4330.2024.07.018

Abstract

Abstract:

【Objective】The purpose of this study is to utilize multispectral unmanned aerial vehicle (UAV) imagery to rapidly, accurately, and non-destructively acquire height information of apple trees, aiming to achieve monitoring of apple tree growth conditions using UAV remote sensing technology and analyze the influence of UAV flight height on the extraction results of tree height. 【Methods】The DJI Phantom 4 multispectral UAV was employed to acquire UAV imagery of apple trees at flight heights of 30, 60, and 90 m, respectively. The acquired imagery was processed using DJI Terra software to generate digital orthophoto models (DOM) and digital surface models (DSM). Based on the generated DOM and DSM, a digital elevation model (DEM) of the study area was created using the Kriging interpolation method. The difference between the DSM and DEM was used to generate the canopy height model (CHM) for extracting tree height. Regression analysis and accuracy validation were conducted by comparing the extracted tree heights with field-measured values.【Results】The average accuracy of tree height extraction at a flight height of 30 m was 88.49%, with an R² value of 0.8378 and an RMSE of 0.403,1 m. At a flight height of 60m, the average accuracy of tree height extraction was 74.72%, with an R² value of 0.657,7 and an RMSE of 0.884,6 m. At a flight height of 90 m, the average accuracy of tree height extraction was 56.20%, with an R² value of 0.527,3 and an RMSE of 1.476,7 m. 【Conclusion】The use of multispectral UAV remote sensing technology enables the extraction of apple tree height possible. The extraction accuracy decreases with an increase in UAV flight height. The best results are obtained at a flight height of 30 m, while the poorest results are obtained at a flight height of 90 m. Within appropriate flight heights, multispectral UAV remote sensing technology can rapidly, accurately, and non-destructively monitor the growth conditions of orchard fruit trees, thereby improving the management efficiency for orchard operators.

Key words: multispectral UAV; flight altitude; apple tree

摘要：

【目的】利用多光谱无人机影像快速、准确、无损的获取苹果树高信息,实现无人机遥感技术对苹果树生长状况的监测,并分析无人机飞行高度对树高提取结果的影响。【方法】利用大疆精灵4多光谱无人机分别获取30、60和90 m飞行高度的苹果树无人机影像,经大疆智图(DJI Terra)软件处理生成DOM和DSM影像数据,基于生成的DOM和DSM,利用克里金插值法生成研究区DEM,将DSM和DEM作差生成苹果树CHM提取树高,与实地测量的果树高值进行回归分析和精度验证。【结果】30 m飞行高度平均树高提取精度为88.49%,R²为0.837 8,RMSE为0.4 031 m;60 m飞行高度平均树高提取精度为74.72%,R²为0.6577,RMSE为0.884 6 m;90 m飞行高度平均树高提取精度为56.20%,R²为0.527 3,RMSE为1.476 7 m。【结论】利用多光谱无人机遥感技术可以实现对苹果树高的提取,提取精度随着无人机飞行高度的增加而降低,30 m飞行高度提取结果最佳,90 m飞行高度提取结果最差。在合适的飞行高度内,多光谱无人机遥感技术可以快速、准确、无损的实现对果园果树生长状况的监测,提高果园的管理效率。

关键词: 多光谱无人机, 飞行高度, 苹果树

CLC Number:

S127

ZHANG Zhenfei, GUO Jing, YAN An, HOU Zhengqing, YUAN Yilin, XIAO Shuting, SUN Zhe. Study on extraction of apple tree height at different flight altitudes using multispectral UAV[J]. Xinjiang Agricultural Sciences, 2024, 61(7): 1710-1716.

张振飞, 郭靖, 颜安, 侯正清, 袁以琳, 肖淑婷, 孙哲. 多光谱无人机不同飞行高度下苹果树高的提取[J]. 新疆农业科学, 2024, 61(7): 1710-1716.

Figures/Tables 6

Fig.1 UAV image stitching process

Fig.2 Elevation sampling points

Fig.3 Digital elevation model of UAV at different flying heights Note:a:30 m flight altitude;b:60 m flight altitude;c:90 m flight altitude

Fig.4 Canopy height model of UAV at different flying heights(CHM) Note:a:30 m flight altitude;b:60 m flight altitude;c:90 m flight altitude

Tab.1 Regression analysis of extracting the measured plant height values and the actual measured plant height values

飞行高度 Flying altitude (m)	精度范围 Accuracy range(%)	平均提取精度 Average extraction accuracy (%)	R²	RMSE (m)
30 60 90	64.26~99.76 10.60~99.90 7.62~91.83	88.49 74.72 56.20	0.837 8 0.657 7 0.527 3	0.403 1 0.884 6 1.476 7

Fig.5 Scatter plot of the relationship between extracted values and measured values of apple plant height at different flight heights Note:Blue,red and green are 30,60 and 90 m scatt plot of flight altitude

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