Remote Sensing Phenology Metrics across the conterminous U.S.
Summary
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. Researchers at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center have developed methods for documenting the seasonal dynamics of vegetation in an operational fashion from satellite time-series data. The researchers produce two suites of phenological metrics data across the conterminous U.S (CONUS) on a yearly basis and release them publicly. The metrics are based on temporally smoothed Normalized Difference Vegetation Index (NDVI) data from two satellite sensors: Collection 6 Aqua Moderate Resolution Imaging Spectroradiometer [...]
Summary
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. Researchers at the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center have developed methods for documenting the seasonal dynamics of vegetation in an operational fashion from satellite time-series data. The researchers produce two suites of phenological metrics data across the conterminous U.S (CONUS) on a yearly basis and release them publicly. The metrics are based on temporally smoothed Normalized Difference Vegetation Index (NDVI) data from two satellite sensors: Collection 6 Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) (2003 – 2020 metrics) and S-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) (2021 metrics). The degradation and the impending decommissioning of the Aqua C6 MODIS sensor prompted the USGS EROS to develop the 2021 CONUS phenology metrics using VIIRS data. Moving forward, the phenological metrics based on eVIIRS NDVI data will be continued.
The temporally smoothed NDVI data were ingested into a model developed in the Interactive Data Language (IDL) to quantify specific phenological events (see 1 - 9 below). For details about the algorithms and the data scaling for each of these seasonal phenological metrics, refer to the data creation process section of the respective metadata. The current suites of eMODIS NDVI (250-m) and eVIIRS NDVI (375-m) spatial resolution phenological metrics are defined as follows:
Start of Season Time (SOST): starting time of the onset of the growing season (in day of the year).
Start of Season NDVI (SOSN): NDVI value at the starting time of the onset of the growing season (unitless based on NDVI units).
End of Season Time (EOST): ending time of the growing season (in day of the year).
End of Season NDVI (EOSN): NDVI value at the ending time of the growing season (unitless-based on NDVI units).
Maximum Time (MAXT): the day of the year when the NDVI reaches its maximum during the growing season (in day of the year).
Maximum NDVI (MAXN): the highest (or peak) value in NDVI observed in a growing season (unitless-based on NDVI units).
Duration (DUR): the length of the growing season-the time between the start of season and end of season (in number of days).
Amplitude (AMP): the difference between the Maximum NDVI and NDVI at the day of start of season (unitless-based on NDVI units).
Time Integrated NDVI (TIN): the cumulative value of NDVI from the start to the end of the growing season (unitless-based on accumulated NDVI units).