Advanced Very High Resolution Radiometer Phenology: 2001-Present

The Remote Sensing Phenology (RSP) collection is a set of nine annual phenological metrics for the conterminous United States. Researchers at the USGS EROS Center utilize data gathered by satellite sensors to track seasonal changes in vegetation. The satellite sensors that provide the raw data are the Advanced Very High Resolution Radiometer (AVHRR) from National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites. The satellite data are initially transformed into Normalized Difference Vegetation Index (NDVI) values. AVHRR NDVI provide the foundation for the phenology metrics. Time-series NDVI can be summarized and analyzed to produce nine key phenological indicators that represent a complete growing season. These data represent a powerful tool for documenting plant life-cycle trends over time and detecting the impacts of climate change on ecosystems.

The complete set of phenological metrics are as follows: 1. Start of Season Time (SOST): starting time of the onset of the growing season (in day of the year). 2. Start of Season NDVI (SOSN): NDVI value at the starting time of the onset of the growing season (unitless- based on NDVI units). 3. End of Season Time (EOST): ending time of the growing season (in day of the year). 4. End of Season NDVI (EOSN): NDVI value at the ending time of the growing season (unitless-based on NDVI units). 5. Maximum Time (MAXT): the day of the year when the NDVI reaches its maximum during the growing season (in day of the year). 6. Maximum NDVI (MAXN): the highest (or peak) value in NDVI observed in a growing season (unitless-based on NDVI units). 7. Duration (DUR): the length of the growing season-the time between the start of season and end of season (in number of days). 8. Amplitude (AMP): the difference between the Maximum NDVI and NDVI at the day of start of season (unitless-based on NDVI units). 9. Time Integrated NDVI (TIN): the cumulative value of NDVI from the start to the end of the growing season.