Start of the Green Season and Normalized Difference Vegetation Index in Alaska’s Arctic National Parks
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Area
2.2. Satellite Data Analysis
- Fit a 90th percentile smoothing spline curve to NDVI vs. ordinal date (1 to 365), using all available years of data.
- Locate the two-week interval with the flattest slope of the curve from step 1 in the fall; “fall” is defined as day number greater than 240 (28 Aug) and smoothed NDVI greater than 0.1 (a level indicating snow cover). Compute the mean NDVI value of this two-week period from the fitted curve (90th percentile) values. This is the assumed NDVI of senesced, snow-free vegetation in the pixel.
- Fit 90th percentile smoothing spline curves to NDVI vs. ordinal date for each individual year.
- Find the date on each annual curve from step (3) where NDVI first crosses the level of senesced vegetation from step (2). This is the start of the green season.
2.3. Ground Verification
3. Results
3.1. Annual NDVI Cycle at the Climate Monitoring Stations
3.2. Comparison with the Camera Observations of Phenology Events
3.3. NDVI Cycle at 210 Systematic Sample Points
4. Discussion and Conclusions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
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Station Name | Symbol | National Park Unit | Latitude (deg) | Longitude (deg) | Elevation (m) | Vegetation |
---|---|---|---|---|---|---|
Kugururok | KUG | Noatak National Preserve | 68.317 | −161.492 | 335 | Open low shrub tundra (Betula, Salix, Ledum, Vaccinium) |
Mt. Noak | MNO | Cape Krusenstern National Monument | 67.141 | −162.995 | 257 | Dwarf shrub tundra (Dryas) |
Pamichtuk Lake | PAM | Gates of the Arctic National Park and Preserve | 67.766 | −152.164 | 1019 | Dwarf shrub tundra (Dryas, Salix) |
Salmon River | SRW | Kobuk Valley National Park | 67.460 | −159.841 | 381 | Mosaic of open low and tall scrub (Betula, Salix, Alnus) |
Serpentine | SRT | Bering Land Bridge National Preserve | 65.852 | −164.708 | 143 | Open low shrub tundra (Betula) |
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Swanson, D.K. Start of the Green Season and Normalized Difference Vegetation Index in Alaska’s Arctic National Parks. Remote Sens. 2021, 13, 2554. https://doi.org/10.3390/rs13132554
Swanson DK. Start of the Green Season and Normalized Difference Vegetation Index in Alaska’s Arctic National Parks. Remote Sensing. 2021; 13(13):2554. https://doi.org/10.3390/rs13132554
Chicago/Turabian StyleSwanson, David K. 2021. "Start of the Green Season and Normalized Difference Vegetation Index in Alaska’s Arctic National Parks" Remote Sensing 13, no. 13: 2554. https://doi.org/10.3390/rs13132554
APA StyleSwanson, D. K. (2021). Start of the Green Season and Normalized Difference Vegetation Index in Alaska’s Arctic National Parks. Remote Sensing, 13(13), 2554. https://doi.org/10.3390/rs13132554