Estimation of maize seedling number based on UAV multispectral data
ZHAO Xiaowei1,2(), HUANG Yang1(), WANG Yongqiang1, CHU Ding1
1. Heilongjiang Provincial Research Institute of Surveying and Mapping, Harbin 150081, China 2. Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China
To monitor and evaluate maize seedlings in Northeast China and estimate their number in time, this study provided effective support for the rapid estimation of the maize seedling number using unmanned aerial vehicle (UAV) remote sensing images. Using the multispectral UAV data, the color indexes ExG, GBDI, ExG-ExR, NGRDI, and GLI were compared to segment maize seedlings from the soil background. Then, the optimal threshold was determined using the Otsu algorithm, and ExG was selected as the optimal color index. According to optimization, the best combination of morphological parameters consists of area (A), perimeter (B), rectangle length (D), rectangle perimeter (G), ellipse long axis length (H), and shape factor (Q). Then, the number of maize seedlings was predicted using the support vector regression (SVR) model and the prediction accuracy was assessed. Finally, the spatial distribution map of the local maize seedling number was developed. Tests revealed that the accuracy and the statistical error of the SVR model were 96.54% and 0.6%, respectively. These results allow the number and growth trends of maize seedlings to be predicted quickly and accurately in a short time.
Xiaowei ZHAO,Yang HUANG,Yongqiang WANG, et al. Estimation of maize seedling number based on UAV multispectral data[J]. Remote Sensing for Natural Resources,
2022, 34(1): 106-114.
Fig.2 Characteristic parameters of original UAV image
Fig.3 Weed removal
Fig.4 Data results of quadrat 23 under different indexes
Fig.5 Weed removal effect of different methods
Fig.6 Training and testing results of estimating number of seedling based on ExG index
指数
训练集
测试集
RMSE
R2
RMSE
R2
NGRDI
0.019 4
0.834 3
0.018 6
0.807 3
ExG-ExR
0.013 1
0.828 6
0.018 7
0.819 8
GBDI
0.014 5
0.832 1
0.019 8
0.802 3
ExG
0.010 3
0.877 2
0.018 7
0.862 6
GLI
0.015 7
0.813 1
0.016 1
0.803 1
Tab.1 Training and testing accuracy of each index
Fig.7 Pearson coefficient of the measured number of characteristic parameters
参数个数
组合方式
最优组合
训练集R2
测试集R2
1
7
A
0.806 8
0.808 1
2
21
AH
0.879 2
0.865 4
3
35
ADH
0.931 7
0.946 7
4
35
ABDF
0.946 2
0.954 8
5
21
ABDFH
0.963 1
0.962 1
6
7
ABDGHQ
0.986 4
0.965 4
7
1
ABDFGHQ
0.954 2
0.961 3
Tab.2 Combination of characteristic parameter
Fig.8 Comparative analysis of measured and predicted plant numbers
实测株数
预测株数
1
2
3
4
5
6
7
相对误差
1
732
22
—
—
—
—
—
0.029
2
9
175
6
—
—
—
—
0.031
3
—
6
68
2
—
—
—
0.105
4
—
—
4
19
1
—
—
0.208
5
—
—
—
2
8
—
—
0.200
6
—
—
—
—
—
1
—
0
7
—
—
—
—
—
—
0
—
Tab.3 Overestimation and underestimation of measured and predicted plant numbers
Fig.9 Object recognition in different monitoring unit scales
Fig.10 Random rectangular plot and emergence rate
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