Estimation of Forest Structural Attributes Using Spectral Indices and Point Clouds from UAS-Based Multispectral and RGB Imageries
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Area
2.2. Field Data
2.3. Remote Sensing Data
2.4. Data Pre-Processing
2.5. Point Cloud Processing
2.6. Image Processing
2.7. Statistical Analysis and Modeling
3. Results
3.1. DAP Point Clouds and Reflectance Imageries Generation
3.2. Structural Metrics Extraction and Analysis
3.3. Forest Structural Attributes Modeling
4. Discussion
5. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Appendix A
References
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Forest Parameters | G1 (n = 17) | G2 (n = 17) | G3 (n = 11) | |||
---|---|---|---|---|---|---|
Range | Mean ± SD | Range | Mean ± SD | Range | Mean ± SD | |
DBH | 10.61–23.39 | 19.96 ± 3.13 | 10.15–20.82 | 17.72 ± 2.68 | 10.49–17.74 | 14.74 ± 2.74 |
HL | 6.69–14.53 | 12.01 ± 1.85 | 6.93–14.60 | 11.23 ± 1.93 | 6.64–12.64 | 10.32 ± 2.15 |
N | 311–495 | 430 ± 57 | 509–608 | 561 ± 36 | 679–1329 | 866 ± 209 |
G | 13.89–57.51 | 44.01 ± 10.89 | 15.22–64.47 | 46.23 ± 12.90 | 20.29–74.82 | 48.58 ± 15.92 |
V | 16.55–105.26 | 74.97 ± 21.95 | 18.50–120.86 | 76.16 ± 26.42 | 24.08–128.81 | 76.61 ± 31.61 |
MicaSense RedEdge | Sony A7R | |
---|---|---|
Flight height (m) | 150 | 350 |
Flight speed (m/s) | 30 | 20 |
Forward overlap (%) | 80 | 75 |
Lateral overlap (%) | 80 | 65 |
Spectral bands | Blue, Green, Red, Red-edge and Near-infrared | Blue, Green and Red |
Optimal resolution | 1280 × 960 | 7360 × 4912 |
ground sample distance (cm) | 10 | 5 |
Image format | 16-bit TIFF (Tagged Image File Format) | 24-bit TIFF |
Metrics | Description |
---|---|
Percentile heights (H25, H50, H75, and H95) | The percentiles of the canopy height distributions (25th, 50th, 75th, and 95th) |
Canopy return density (D1, D3, D5, D7, and D9) | The proportion of points above the quantiles (10th, 30th, 50th, 70th, and 90th) to total number of points |
Mean/Maximum height (Hmean/Hmax) | Mean/maximum height above ground of all points |
Coefficient of variation of heights (Hcv) | Coefficient of variation of heights of all points |
Open and Closed gap zones of Canopy volume models (CVM) (i.e., Open and Closed) | The empty voxels located above and below the canopy |
Euphotic and Oligophotic zones of CVM (i.e., E and O) | The voxels located within an uppermost percentile (65%) of all filled grid cells of that column, and voxels located below the point in the profile |
α and β parameter of Weibull distribution (i.e., Wα and Wβ) | The α and β parameter of the Weibull distribution fitted to foliage density profile |
Vegetation Index | Equation | Reference |
---|---|---|
Atmospherically Resistant Vegetation Index (ARVI) | (ρnir − ρrb)/(ρnir + ρrb), ρrb = ρred − γ (ρblue − ρred), γ=0.5 | [47] |
Difference Vegetation Index (DVI) | ρnir − ρred | [48] |
Enhanced Vegetation Index (EVI) | 2.5(ρnir − ρred)/(ρnir + 6ρred − 7.5ρblue +1) | [49] |
Global Environment Monitoring Index (GEMI) | n(1 − 0.25n)(ρred − 0.125)/(1 − ρred), n = [2(ρnir2 − ρred2) + 1.5ρnir + 0.5ρred]/(ρnir + ρred + 0.5) | [50] |
Green Normalized Difference Vegetation Index (GNDVI) | (ρnir − ρgreen)/(ρnir + ρgreen) | [50] |
Infrared Percentage Vegetation Index (IPVI) | ρnir/(ρnir + ρred) | [51] |
Red Green Ratio Index (RGRI) | ρred − ρgreen | [52] |
Modified Soil Adjusted Vegetation Index (MSAVI) | [2ρnir + 1 − [(2ρnir + 1)2 − 8(ρnir − ρred)]0.5]/2 | [53] |
Modified Simple Ratio Vegetation Index (MSR) | ρred/(ρnir/ρred + 1)0.5 | [53] |
Modified Triangular Vegetation Index (MTVI) | [1.5(1.2(ρnir − ρgreen) − 2.5(ρred − ρgreen)]/[(2ρnir + 1)2 − (6ρnir − 5ρred0.5) − 0.5]0.5 | [53] |
Normalized Difference Vegetation Index (NDVI) | (ρnir − ρred)/(ρnir + ρred) | [53] |
Optimized Soil Adjusted Vegetation Index (OSAVI) | (ρnir − ρred)/(ρnir + ρred + 0.16) | [54] |
Renormalized Difference Vegetation Index (RDVI) | (ρnir − ρred)/(ρnir + ρred) 0.5 | [53] |
Ratio Vegetation Index (RVI) | ρred/ρnir | [55] |
Soil and Atmospherically Resistant Vegetation Index (SARVI) | (1 + 0.5)(ρnir − ρrb)/(ρnir + ρrb + 0.5), ρrb = ρred − γ(ρblue -ρred), γ = 0.5 | [53] |
Soil Adjusted Vegetation Index (SAVI) | (1 + 0.5)(ρnir − ρred)/(ρnir + ρred + 0.5) | [53] |
Simple Ration Vegetation Index (SR) | ρnir/ρred | [56] |
Simple Ratio × Normalized Difference Vegetation Index (SR × NDVI) | (ρnir2 − ρred)/(ρnir + ρred2) | [57] |
G/R (GR) | ρgreen/ρred | [58] |
Brightness (BI) | ρgreen + ρred + ρblue | [58] |
Normalized Greenness (Norm G) | ρgreen/(ρgreen + ρred + ρblue) | [58] |
Normalized Green-Red Ratio (Norm GR) | (ρgreen − ρred)/(ρgreen + ρred) | [58] |
Models | Number of Components | Total Explained Variability (%) | R2 | RMSE | rRMSE (%) |
---|---|---|---|---|---|
Spectral metrics | |||||
HLa | 3 | 99.33 | 0.69 | 1.23 | 10.88 |
HLb | 3 | 98.30 | 0.71 | 1.20 | 9.99 |
HLc | 2 | 97.84 | 0.73 | 1.12 | 9.97 |
HLd | 3 | 99.78 | 0.73 | 1.03 | 9.99 |
Va | 2 | 95.99 | 0.62 | 14.14 | 18.65 |
Vb | 2 | 96.09 | 0.64 | 13.95 | 18.61 |
Vc | 3 | 98.08 | 0.70 | 13.50 | 17.73 |
Vd | 2 | 98.50 | 0.69 | 13.62 | 17.78 |
Combined spectral and structural metrics | |||||
HLa | 3 | 96.20 | 0.92 | 0.55 | 4.86 |
HLb | 3 | 96.11 | 0.93 | 0.53 | 4.41 |
HLc | 3 | 96.34 | 0.93 | 0.49 | 4.36 |
HLd | 2 | 98.11 | 0.94 | 0.44 | 4.26 |
Va | 2 | 94.43 | 0.82 | 11.06 | 14.59 |
Vb | 3 | 97.85 | 0.84 | 10.74 | 14.33 |
Vc | 3 | 96.75 | 0.85 | 10.72 | 14.08 |
Vd | 3 | 97.95 | 0.87 | 10.16 | 13.26 |
Models | Number of Components | Total Explained Variability (%) | R2 | RMSE | rRMSE (%) |
---|---|---|---|---|---|
Spectral metrics | |||||
HLa | 3 | 99.71 | 0.58 | 1.63 | 14.41 |
HLb | 3 | 99.83 | 0.59 | 1.60 | 13.32 |
HLc | 4 | 99.82 | 0.63 | 1.49 | 13.27 |
HLd | 3 | 99.90 | 0.64 | 1.36 | 13.18 |
Va | 4 | 99.84 | 0.56 | 16.62 | 21.92 |
Vb | 3 | 99.85 | 0.60 | 15.99 | 21.33 |
Vc | 3 | 94.40 | 0.61 | 15.87 | 20.84 |
Vd | 2 | 92.73 | 0.60 | 16.17 | 21.10 |
Combined spectral and structural metrics | |||||
HLa | 3 | 93.56 | 0.93 | 0.52 | 4.60 |
HLb | 3 | 94.02 | 0.94 | 0.50 | 4.16 |
HLc | 2 | 97.03 | 0.94 | 0.46 | 4.10 |
HLd | 2 | 95.35 | 0.96 | 0.42 | 4.07 |
Va | 4 | 93.18 | 0.82 | 10.74 | 14.17 |
Vb | 3 | 93.33 | 0.84 | 10.61 | 14.15 |
Vc | 2 | 92.91 | 0.85 | 10.52 | 13.81 |
Vd | 3 | 94.47 | 0.88 | 9.82 | 12.82 |
Models | Number of Components | Total Explained Variability (%) | R2 | RMSE | rRMSE (%) |
---|---|---|---|---|---|
HLa | 2 | 97.72 | 0.94 | 0.48 | 4.24 |
HLb | 2 | 95.53 | 0.94 | 0.45 | 3.75 |
HLc | 2 | 94.46 | 0.96 | 0.34 | 3.03 |
HLd | 2 | 97.95 | 0.97 | 0.30 | 2.91 |
Va | 2 | 92.10 | 0.83 | 10.43 | 13.76 |
Vb | 3 | 94.27 | 0.87 | 9.82 | 13.10 |
Vc | 2 | 95.00 | 0.89 | 8.87 | 11.65 |
Vd | 3 | 95.34 | 0.90 | 8.18 | 10.68 |
Platforms | Sensors | Study Area | Forest Types | Estimated Forest Attributes | Accuracy of Models (rRMSE %) | References |
---|---|---|---|---|---|---|
Mx-Sight | Panasonic Lumix DMC-GF1 | Alcolea, Spain | Subtropical forest | Mean height | 11.5 | [67] |
DJI S800 | Sony NEX-5R | South and southeast of Prague, Czech Republic | Temperate forest | Mean height, Crown diameter | 11.42–12.62 and 14.29–18.56 | [21] |
SenseFly eBee | Canon S110 NIR | Våler municipality, Norway | Boreal forest | HL, Dominate height, N, G, V | 13.3, 3.5, 39.2, 15.4, and 14.5 | [40] |
DJI Phantom 4 | 1/2.3 CMOS | Oita, Japan | Temperate forest | HL, Mean height, Maximum height, V | 6.65, 7.50, 6.17, and 20.02 | [68] |
- | Voxel UltraCamX | northern Vancouver Island, Canada | temperate rainforest | HL, G, V | 14.00, 37.68, and 36.87 | [29] |
Gatewing X100 | Ricoh GR3 | village of Felenne, Belgium | Temperate forest | Dominate height | 8.40 | [66] |
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Share and Cite
Shen, X.; Cao, L.; Yang, B.; Xu, Z.; Wang, G. Estimation of Forest Structural Attributes Using Spectral Indices and Point Clouds from UAS-Based Multispectral and RGB Imageries. Remote Sens. 2019, 11, 800. https://doi.org/10.3390/rs11070800
Shen X, Cao L, Yang B, Xu Z, Wang G. Estimation of Forest Structural Attributes Using Spectral Indices and Point Clouds from UAS-Based Multispectral and RGB Imageries. Remote Sensing. 2019; 11(7):800. https://doi.org/10.3390/rs11070800
Chicago/Turabian StyleShen, Xin, Lin Cao, Bisheng Yang, Zhong Xu, and Guibin Wang. 2019. "Estimation of Forest Structural Attributes Using Spectral Indices and Point Clouds from UAS-Based Multispectral and RGB Imageries" Remote Sensing 11, no. 7: 800. https://doi.org/10.3390/rs11070800
APA StyleShen, X., Cao, L., Yang, B., Xu, Z., & Wang, G. (2019). Estimation of Forest Structural Attributes Using Spectral Indices and Point Clouds from UAS-Based Multispectral and RGB Imageries. Remote Sensing, 11(7), 800. https://doi.org/10.3390/rs11070800