Scientia Agricultura Sinica ›› 2020, Vol. 53 ›› Issue (9): 1795-1805.doi: 10.3864/j.issn.0578-1752.2020.09.008

• TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY·AGRICULTURE INFORMATION TECHNOLOGY • Previous Articles     Next Articles

LAI Estimation Based on Multi-Spectral Remote Sensing of UAV and Its Application in Saline Soil Improvement

FengZhi SHI1,2,RuiYan WANG1,2(),YuHuan LI1,2,Hong YAN3,XiaoXin ZHANG1   

  1. 1 College of Resources and Environment, Shandong Agricultural University, Tai’an 271018, Shandong;
    2 National Engineering Laboratory for Efficient Utilization of Soil and Fertilizer Resources, Tai’an 271018, Shandong;
    3 Agricultural and Rural Bureau of Shanghe County, Shanghe 276200, Shandong
  • Received:2019-08-23 Accepted:2020-03-07 Online:2020-05-01 Published:2020-05-13
  • Contact: RuiYan WANG E-mail:wry@sdau.edu.cn

Abstract:

【Objective】Vegetation yield can comprehensively and intuitively reflect the improvement effect of saline soil. Leaf area index (LAI) of winter wheat during its vigorous growth period is a commonly used measure of vegetation yield. In this study, unmanned aerial vehicle (UAV) multispectral remote sensing was used to obtain the LAI distribution data of winter wheat during its vigorous growth period to objectively and accurately evaluate the improvement effect of saline soil, so as to provide scientific guidance for people to screen saline soil improvement technology and products. 【Method】Taking the experimental area of coastal saline soil improvement in Bohai granary in Wudi county as the research area, based on UAV multispectral remote sensing data, linear regression analysis, partial least squares, random forest, and support vector machine were used to construct LAI inversion model of winter wheat. The factor analysis method was used to evaluate the improvement effect of the sampled land in saline soil area, and the LAI evaluation model of saline soil improvement effect was established to evaluate the improvement effect of saline soil in the entire experimental area. 【Result】The results showed that, for the winter wheat LAI remote sensing estimation, it was not that the higher the resolution, the better, but the smoothed 5×5 mean spectral data corresponded best to the LAI of a ridge of wheat. Among the LAI remote sensing estimation models, the models were built by using SVM with the highest accuracy. The prediction result of the improvement effect LAI evaluation model showed that the prediction accuracy of the improvement effect of saline soil by LAI was higher, and the best improvement land numbers were 26, 27, 28, 29, 30, and 31, and the optimal improvement method was cited. The best improvement method was comprehensive improvement measures of diversion irrigation and adding organic fertilizer. 【Conclusion】UAV remote sensing could accurately invert the LAI of winter wheat at the jointing stage in saline soil area. The evaluation of the improvement effect of saline soil based on the results of LAI inversion could locate the optimal improvement effect from many experimental plots. Compared with the traditional method, this method had the advantages of low cost and high accuracy. The research results had a broad prospect and could provide important technical support for the improvement of saline soil.

Key words: multi-spectral of UAV, improvement effect of saline soil, jointing stage of winter wheat, leaf area index, remote sensing estimation

Fig. 1

The experimental region and sample sites"

Table 1

Correlation between characteristic band and LAI after different filtering windows"

不同窗口
Different window
波段名称Band name
1×1 2×2 3×3 4×4 5×5 6×6 7×7
绿光GRE -0.53** -0.54** -0.54** -0.58** -0.57** -0.58** -0.58**
红光RED -0.58** -0.60** -0.59** -0.60** -0.61** -0.59** -0.61**
红边REG -0.18 -0.19 -0.25* -0.32** -0.34** -0.43** -0.38**
近红NIR 0.55** 0.55** 0.53** 0.47** 0.49** 0.38** 0.45**

Table 2

Vegetation indexes and formulas"

植被指数 Vegetation index 计算公式 Calculation formula
归一化植被指数
NDVI[25]
NDVI=(ρnirred)/(ρnirred)
比值植被指数
RVI[26]
RVI=ρnirred
绿度归一化植被指数
GNDVI[27]
GNDVI=(ρnirgre)/(ρnirgre)
绿色比值植被指数
GRVI[28]
GRVI=ρnirgre

Table 3

Correlation between spectral index and leaf area index after six filtering treatments"

不同窗口
Different window
植被指数 Vegetation index
1×1 2×2 3×3 4×4 5×5 6×6 7×7
NDVI 0.62** 0.66** 0.64** 0.66** 0.67** 0.62** 0.67**
RVI 0.78** 0.80** 0.81** 0.81** 0.82** 0.79** 0.79**
GNDVI 0.59** 0.63** 0.62** 0.67** 0.66** 0.63** 0.67**
GRVI 0.75** 0.79** 0.77** 0.79** 0.79** 0.77** 0.79**
(G+R)/NIR 0.55** 0.58** 0.57** 0.60** 0.60** 0.56** 0.61**

Table 4

Modeling and verification of vegetation index and LAI"

建模集Modeling set (n=44) 验证集Validation set (n=19)
多元线性回归
Multiple linear regression
偏最小二乘
PLS
支持向量机
SVM
随机森林
RF
多元线性回归
Multiple linear regression
偏最小二乘
PLS
支持向量机
SVM
随机森林
RF
R2 0.84 0.75 0.85 0.94 0.69 0.66 0.62 0.56
RMSE 0.51 0.63 0.48 0.32 0.66 0.67 0.74 0.79
RPD 2.30 1.70 2.40 3.50 1.40 1.50 1.30 1.20

Fig. 2

Comparison of measured and predicted values of winter wheat LAI"

Fig. 3

Leaf area index grade distribution map"

Table 5

Total variance analysis"

成分Ingredient 初始特征值Initial eigenvalue 提取载荷平方和Extract load sum of squares 旋转载荷平方和Sum of rotation load squares
总计
Total
方差百分比
Variance percentage
累积
Accumulation (%)
总计
Total
方差百分比
Variance percentage (%)
累积Accumulation (%) 总计
Total
方差百分比
Variance percentage
累积
Accumulation
(%)
1 2.330 58.248 58.248 2.330 58.248 58.248 2.114 52.852 52.852
2 0.959 23.987 82.235 0.959 23.987 82.235 1.175 29.383 82.235
3 0.458 11.445 93.680
4 0.253 6.320 100.000

Table 6

Component score matrix"

成分1
Ingredient 1
成分2
Ingredient 2
有机质Organic matter 0.411 -0.023
盐分Salinity -0.275 -0.260
含氮量Nitrogen content 0.502 -0.263
水分Moisture -0.171 0.899

Table 7

Ranking of scores by parcel"

地块编号
Parcel number
得分
Score
LAI 排名
Ranking
地块编号
Parcel number
得分
Score
LAI 排名
Ranking
地块编号
Parcel number
得分
Score
LAI 排名
Ranking
6 0.67 4.76 1 9 0.42 2.35 7 12 0.33 1.55 12
1 0.59 3.84 2 15 0.42 2.40 6 13 0.32 1.88 11
8 0.49 2.81 4 10 0.39 2.51 8 16 0.22 1.70 13
5 0.48 3.24 3 18 0.34 2.19 9 17 0.02 1.39 14
11 0.46 2.66 5 14 0.33 1.76 10

Fig. 4

Experimental field improvement level classification map"

Fig. 5

Four kinds of window filter processing false color synthesis UAV image (black spot is sampling point)"

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