Exotic annual grass (EAG) phenology estimates in the western U.S. rangelands based on 30-m HLS NDVI (ver. 3.0, September 2024)

Phenological dynamics of terrestrial ecosystems reflect the response of the Earth's vegetation canopy to changes in climate and hydrology and are thus important to monitor operationally. The Exotic Annual Grass (EAG) phenology in the western U.S. rangeland based on 30m near seamless Harmonized Landsat and Sentinel-2 (HLS) Normalized Difference Vegetation Index (NDVI) weekly composites between 2016 and 2021 (Dahal et al., 2022) were processed using these 3 methods: (1) NDVI threshold-based method, (2) manual phenological metrics, and (3) modeling and mapping. The EAG phenology model produced two metrics identifying the sustainable growth characteristics of 16 EAG species throughout level III Commission for Environmental Cooperation ecoregions, which cover over 190 million hectares of western U.S. potential rangeland for 2017 to 2021. The current suites of 30-m spatial resolution phenological metrics are Start of Season Time (SOST); Start of Season NDVI (SOSN); End of Season Time (EOST); End of Season NDVI (EOSN); Maximum Time (MAXT); Maximum NDVI (MAXN); Duration (DUR); and Amplitude (AMP). Datasets 2017 to 2021 were developed using manually interpreted training data from their respective year, but 2022 and 2023 were developed from unseen NDVI datasets to test robustness of the phenology model.

References:
Dahal, D.; Pastick, N.J.; Boyte, S.P.; Parajuli, S.; Oimoen, M.J.; Megard, L.J. Multi-Species Inference of Exotic Annual and Native Perennial Grasses in Rangelands of the Western United States Using Harmonized Landsat and Sentinel-2 Data. Remote Sensing 2022, 14, doi:10.3390/rs14040807.