A Combined Strategy of Improved Variable Selection and Ensemble Algorithm to Map the Growing Stem Volume of Planted Coniferous Forest
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Area
2.2. Framework of This Research
2.3. Ground Data Collection and Processing
2.4. Remote Sensing Images and Pre-Processing
2.5. Extraction of Variables
2.6. Proposed Variable Selection Criterion
2.7. Secondary Ensemble with Improved Weighted Average Approach
2.7.1. Secondary Ensemble Algorithm
2.7.2. Accuracy Evaluation
3. Results
3.1. The Results of Variables Selection
3.2. The Result of the Secondary Ensemble
3.3. Mapping the Forest GSV
4. Discussion
4.1. Variable Selection
4.2. Ensemble Model
5. Conclusions
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Tree Species | Number of Plots | The Range of GSV | The Average GSV | STD |
---|---|---|---|---|
Larch | 38 | 86.17~405.56 | 208.38 | 81.84 |
Chinese pine | 43 | 91.97~514.96 | 253.32 | 112.75 |
Sensors | Acquisition Date | Spectral Bands/Polarizations |
---|---|---|
Sentinel-1A (level-1GRD) | 19 September 2017 | VH, VV |
Sentinel-2A (level-1C) | 22 September 2017 | Band2, Band3, Band4, Band5, Band6, Band7, Band8, Band8A |
Variable Type | Variable Name | Description of Variables | Sensors |
---|---|---|---|
Vegetation Index | Enhanced Vegetation Index (EVI) | 2.5 × (Band8 − Band4)/(Band8 + 6 Band4 − 7.5 × Band2 + 1) | Sentinel-2A |
Enhanced Vegetation Index-2 (EVI-2) | 2.5 × (Band8 − Band4)/(Band8 + 2.4 × Band4 + 1) | Sentinel-2A | |
Normalized Difference Vegetation Index (NDVI) | (Band8 − Band4)/(Band8 + Band4) | Sentinel-2A | |
Ratio Vegetation Index (RVI) | Band8/Band4 | Sentinel-2A | |
Spectral Vegetation Index (SVI) | Band4/Band8 | Sentinel-2A | |
Soil Adjusted Vegetation Index (SAVI) | (1 + L) × (Band8 − Band4)/(Band8 + Band4 + L) L = 0.5 in most conditions | Sentinel-2A | |
Spectral reflection | Spectral bands | Band2, Band3, Band4, Band5, Band6, Band7, Band8, Band8A | Sentinel-2A |
Features of SAR | Backscattering coefficient | VH, VV, VH/VV | Sentinel-1A |
Texture features | Mean, Variance, Contrast, Entropy, Homogeneity, Dissimilarity, Entropy, Second moment, Correlation | Gray Level Co-occurrence Matrix (GLCM) with size of 3 × 3 | Sentinel-1A Sentinel-2A |
Variable Selection Criterion | Method of Ranking | Models | The First Selected Variable | Number of Variables | Number of Operations |
---|---|---|---|---|---|
Forward | FORW | CART | band4 | 2 | 295 |
FORW | KNN | band4 | 10 | 1034 | |
FORW | ANN | EVI_2 | 4 | 486 | |
FORW | SVR | EVI | 6 | 672 | |
The proposed criterion for variable selection | RF | CART | EVI_2 | 6 | 41 |
RF | KNN | EVI_2 | 6 | 27 | |
RF | ANN | EVI_2 | 4 | 51 | |
RF | SVR | EVI_2 | 6 | 43 | |
DC | CART | band4_M | 4 | 67 | |
DC | KNN | band4_M | 5 | 26 | |
DC | ANN | band4_M | 4 | 58 | |
DC | SVR | band4_M | 7 | 64 | |
MIC | CART | band4_M | 4 | 95 | |
MIC | KNN | band4_M | 9 | 37 | |
MIC | ANN | band4_M | 5 | 46 | |
MIC | SVR | band4_M | 5 | 44 | |
PCC | CART | RVI | 7 | 20 | |
PCC | KNN | RVI | 5 | 21 | |
PCC | ANN | RVI | 4 | 65 | |
PCC | SVR | RVI | 7 | 59 |
Ranking Methods | First Ensemble (Bagging and AdaBoost) | Secondary Ensemble (IWA) | |||||
---|---|---|---|---|---|---|---|
Number of Variables | rRMSE (%) | R2 | Number of Models | Number of Related Variables | rRMSE (%) | R2 | |
RF | 4~6 | 21.91~30.28 | 0.47~0.72 | 3 | 7 | 20.14 | 0.77 |
DC | 4~7 | 23.41~28.89 | 0.52~0.68 | 8 | 14 | 21.34 | 0.74 |
MIC | 4~9 | 23.60~31.49 | 0.43~0.68 | 5 | 13 | 19.89 | 0.77 |
PCC | 4~7 | 21.93~28.83 | 0.52~0.72 | 8 | 15 | 18.89 | 0.79 |
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Xu, X.; Lin, H.; Liu, Z.; Ye, Z.; Li, X.; Long, J. A Combined Strategy of Improved Variable Selection and Ensemble Algorithm to Map the Growing Stem Volume of Planted Coniferous Forest. Remote Sens. 2021, 13, 4631. https://doi.org/10.3390/rs13224631
Xu X, Lin H, Liu Z, Ye Z, Li X, Long J. A Combined Strategy of Improved Variable Selection and Ensemble Algorithm to Map the Growing Stem Volume of Planted Coniferous Forest. Remote Sensing. 2021; 13(22):4631. https://doi.org/10.3390/rs13224631
Chicago/Turabian StyleXu, Xiaodong, Hui Lin, Zhaohua Liu, Zilin Ye, Xinyu Li, and Jiangping Long. 2021. "A Combined Strategy of Improved Variable Selection and Ensemble Algorithm to Map the Growing Stem Volume of Planted Coniferous Forest" Remote Sensing 13, no. 22: 4631. https://doi.org/10.3390/rs13224631
APA StyleXu, X., Lin, H., Liu, Z., Ye, Z., Li, X., & Long, J. (2021). A Combined Strategy of Improved Variable Selection and Ensemble Algorithm to Map the Growing Stem Volume of Planted Coniferous Forest. Remote Sensing, 13(22), 4631. https://doi.org/10.3390/rs13224631