The Impact of NPV on the Spectral Parameters in the Yellow-Edge, Red-Edge and NIR Shoulder Wavelength Regions in Grasslands
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Area
2.2. Data Collection
2.3. Automatic Extraction of Spectral Parameters of Yellow-Edge, Red-Edge and NIR Shoulder
2.4. The Relationship between Dead Cover and the Spectral Parameters of Yellow-Edge, Red-Edge and NIR Shoulder
2.5. The Imapct of NPV on LAI Estimation by the Spectral Parameters
3. Results
3.1. The Relationship of the Spectral Parameters of Yellow-Edge, Red-Edge and NIR Shoulder with Dead Cover
3.2. The Relationship between NDVI and Dead Cover
3.3. Influence of Dead Cover on LAI Estimation by NDVI and Spectral Parameters of Yellow-Edge, Red-Edge and NIR Shoulder and Dead Cover
4. Discussion
4.1. The Influence of Dead Materials on the Spectral Parameters of Yellow-Edge, Red-Edge and NIR Shoulder
4.2. The Impact of Dead Cover on LAI Estimation
5. Conclusions
Supplementary Materials
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Appendix A
The Slope of Yellow-Edge | The Slope of Red-Edge | The Slope of NIR Shoulder | Hyperspectral NDVI | NDVI Using Red Valley | LAI | Red-Edge Position | |
---|---|---|---|---|---|---|---|
The slope of yellow-edge | −0.94 * | −0.60 * | −0.94 * | −0.94 * | −0.71 * | −0.53 * | |
The slope of red-edge | 0.70 * | 0.95 * | 0.95 * | 0.76 * | 0.63 * | ||
The slope of NIR shoulder | 0.65 * | 0.65 * | 0.45 * | 0.41 * | |||
Hyperspectral NDVI | 1 * | 0.78 * | 0.68 * | ||||
NDVI using red valley | 0.79 * | 0.69 * | |||||
LAI | 0.63 * | ||||||
Red-edge position |
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Sites | Statistics | Green Cover (%) | Dead Cover (%) | Bare Soil (%) | LAI | Hyperspectral NDVI |
---|---|---|---|---|---|---|
All data | Maximum | 97 | 99 | 90 | 6.270 | 0.954 |
Minimum | 0 | 0 | 0 | 0.100 | 0.067 | |
Mean | 30.841 | 50.895 | 16.089 | 1.556 | 0.403 | |
Median | 16 | 57 | 10 | 1.080 | 0.277 | |
Standard deviation | 29.815 | 26.048 | 18.101 | 1.196 | 0.263 | |
Transects in GNP | Maximum | 50 | 99 | 89 | 4.130 | 0.648 |
Minimum | 0 | 4 | 0 | 0.100 | 0.067 | |
Mean | 11.310 | 66.468 | 19.414 | 0.965 | 0.224 | |
Median | 10 | 69 | 15 | 0.810 | 0.216 | |
Standard deviation | 6.732 | 15.462 | 16.727 | 0.608 | 0.069 | |
Sites in GNP | Maximum | 95 | 90 | 90 | 5.560 | 0.954 |
Minimum | 5 | 0 | 0 | 0.100 | 0.088 | |
Mean | 43.166 | 34.456 | 20.188 | 1.921 | 0.539 | |
Median | 40 | 35 | 10 | 1.760 | 0.514 | |
Standard deviation | 18.186 | 20.406 | 21.996 | 1.217 | 0.156 | |
Sites in WNP | Maximum | 97 | 90 | 10 | 6.270 | 0.940 |
Minimum | 10 | 3 | 0 | 1.560 | 0.566 | |
Mean | 83.492 | 16.442 | 0.066 | 3.339 | 0.860 | |
Median | 87 | 13 | 0 | 3.320 | 0.868 | |
Standard deviation | 12.521 | 12.447 | 0.697 | 0.703 | 0.040 |
Spectral Parameters | Description |
---|---|
R segmentation | Wavelength of the change-point between yellow-edge and red-edge (the first turning point from segmented linear regression in the 600–900 nm regions). |
NIR segmentation | Wavelength of the change-point between red-edge and NIR shoulder (the second turning point from segmented linear regression in the 600–900 nm regions). |
The slope of yellow-edge | The slope of the linear regression between the reflectance and wavelength in yellow-edge (550–640 nm [23]; from 600 nm to R segmentation in this study). |
Red valley position | Wavelength of the strongest absorption in the transition between yellow-edge and red-edge (650–690 nm [23,33]; wavelength of the lowest reflectance between 600 nm to the R segmentation in this study). |
The slope of red-edge | The slope of the linear regression between the reflectance and wavelength in red-edge (680–760 nm [23,29]; from R segmentation to NIR segmentation in this study). |
Red-edge position | Wavelength corresponding to the maximum slope in the 680–760 nm regions [23,34] (the middle position between R segmentation and NIR segmentation in this study). |
The slope of NIR shoulder | The slope of the linear regression between the reflectance and wavelength in NIR shoulder (750–900 nm [20]; from NIR segmentation to 900 nm in this study). |
Coverage | The Slope of Red-Edge | The Slope of Yellow-Edge | The Slope of NIR Shoulder | Red-Edge Position | Red Valley Position | Hyperspectral NDVI | NDVI Using Red Valley |
---|---|---|---|---|---|---|---|
Dead materials 1 | 0.141% * | 0.626% * | 0.003% * | 0.009% | 0.919% * | 0.465% * | 0.389% * |
Green vegetation 1 | 81.295% * | 78.628% * | 27.970% * | 88.988% * | 69.942% * | 89.432% * | 89.902% * |
Bare soil 1 | 0.038% * | 0.700% * | 0.003% * | 0.450% * | 1.116% * | 0.153% * | 0.079% * |
Spectral Parameters | Linear Regression for LAI Estimation | Residual and Dead Cover 2 | ||||||
---|---|---|---|---|---|---|---|---|
R2 | Adjusted R2 | RMSE 1 | Slope | Intercept | Threshold | Std. Error 3 | Correlation 4 | |
Hyperspectral NDVI | 0.601 * | 0.601 * | 0.751 | 3.48 * | 0.20 * | 72.32 * | 0.81 | 0.497 * |
NDVI using red valley | 0.618 * | 0.618 * | 0.736 | 3.69 * | 0.05 * | 72.39 * | 0.85 | 0.484 * |
The slope of red-edge | 0.580 * | 0.580 * | 0.771 | 0.42 * | 0.63 | 73.69 * | 0.88 | 0.475 * |
The slope of yellow-edge | 0.498 * | 0.498 * | 0.843 | –5.38 * | 1.57 * | 71.61 * | 0.75 | 0.539 * |
The slope of NIR shoulder | 0.203 * | 0.202 * | 1.063 | 8.31 * | –0.53 * | 66.64 * | 0.92 | 0.435 * |
Red-edge position | 0.402 * | 0.401 * | 0.920 | 0.17 * | –122.50 * | 74.51 * | 0.94 | 0.357 * |
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Xu, D.; Liu, Y.; Xu, W.; Guo, X. The Impact of NPV on the Spectral Parameters in the Yellow-Edge, Red-Edge and NIR Shoulder Wavelength Regions in Grasslands. Remote Sens. 2022, 14, 3031. https://doi.org/10.3390/rs14133031
Xu D, Liu Y, Xu W, Guo X. The Impact of NPV on the Spectral Parameters in the Yellow-Edge, Red-Edge and NIR Shoulder Wavelength Regions in Grasslands. Remote Sensing. 2022; 14(13):3031. https://doi.org/10.3390/rs14133031
Chicago/Turabian StyleXu, Dandan, Yanqing Liu, Weixin Xu, and Xulin Guo. 2022. "The Impact of NPV on the Spectral Parameters in the Yellow-Edge, Red-Edge and NIR Shoulder Wavelength Regions in Grasslands" Remote Sensing 14, no. 13: 3031. https://doi.org/10.3390/rs14133031
APA StyleXu, D., Liu, Y., Xu, W., & Guo, X. (2022). The Impact of NPV on the Spectral Parameters in the Yellow-Edge, Red-Edge and NIR Shoulder Wavelength Regions in Grasslands. Remote Sensing, 14(13), 3031. https://doi.org/10.3390/rs14133031