Crop/Pasture phenology is very important reference information to calculate the seasonal indictors in ASIS. As the calculation of seasonal indictors (ASI, Drought Intensity and Mean VHI) includes the use of crop coefficients, which introduces sensitivity of a crop to water stress during each phenological phase.
In ASIS, the crop/pasture phenology are described by two datasets: Growing Seasons and Progress of Seasons.
The Growing Seasons summarize three benchmark stages of crop/grassland: Start of Season (SOS), Maximum of Season (MOS) and End of Season (EOS).
The Start of Season (SOS) indicates the early stage of crop/grass emergence, defined as the date when the rising NDVI-curve cuts the threshold NDVIs.
The Maximum of Season (MOS) indicates when crop/grass foliage is fully developed, defined as the date when the NDVI is at its maximum value.
The End of Season (EOS) indicates when crop/grass has reached physiological maturity, defined as the date when the descending NDVI-curve crosses NDVIe. This date does not necessarily correspond to the harvest period.
The Progress of Season (POS) depicts the development of crops/pastures during the growing season: for any dekad (a 10-day period), the map indicates how far the season has progressed. The POS is based on the Long Term Average (LTA) of vegetation phenology for each pixel. This simplification implies that the crop/pasture phenology is static and, therefore, the growing seasons progress at a constant rate each year. Each pixel’s “normal” temporal behaviour in the course of the year is represented by 36 dekadal LTA images of NDVI. From these standardized curves, each pixel’s phenology is then derived.
The “seasonal progress” is expressed in relative terms via a fixed set of “POS images”. For any dekad in the year, they indicate for each pixel how the season has progressed. That can be a value between 0 and 100 percent (i.e. 50 percent is the mid-point of the growing season).
Global ASIS covers two crop/pasture seasons. Some countries have three or four crop seasons within a crop year. For these countries, Global ASIS cannot properly capture the crop phenology between the first and the last season (e.g. for a country has four crop seasons, the crop phenology of the 2nd and 3rd season).
More information can be found here
