Phenology is defined as the study of the timing of recurring biological cycles and their connection to the climate. Changes in the vegetation phenology, including the start of season, the length of the season as well as the end of season impacts the ecosystem functioning such as carbon storage, water holding capacity and agricultural productivity.
Crop/pasture phenology maps depict the progress of the seasons. It is based on the long-term average of vegetation phenology for each pixel (In ASIS, Cropland/Grassland masks are applied. Pixel with at least 5% covered by the class are defined as a cropland/grassland pixel). This simplification implies that the crop/pasture phenology is static and therefore the growing seasons progress at a constant rate each year. The progress of growing seasons are described by three major phases: Start of Season (SOS), Maximum of Season (MOS) and End of Season (EOS).
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:
NDVIs=NDVImins + Ts.(NDVImax – NDVImins)
NDVImax is the NDVI at the maximum of the cycle, NDVImins is the minimum before this maximum and threshold Ts is fixed to 0.25 for all land cover types. SOS is searched leftwards from NDVImax to NDVImins.
Maximum of Season (MOS) indicates when crop/grass foliage is fully developed, defined as the date when the NDVI is at its maximum value.
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.
NDVIe=NDVImine + Te.(NDVImax – NDVimine)
NDVImax is the NDVI at the maximum of the cycle, NDVImine is the minimum after this maximum and threshold Te is set to 0.75 for cropland and to 0.25 for all other land. EOS is searched rightwards from NDVImax to NDVImine.
Map legend label and pixel value mapping (half open intervals):
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October Y-1: (-36)-(-6);
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November - December Y-1: (-6)-0;
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January - February: 0-6;
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March - April: 6-12;
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May - June: 12-18;
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July - August: 18-24;
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September - October: 24-30;
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November - December: 30-36;
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January - February Y+1: 36-42;
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March Y+1: 42-72.
Map flags:
- no seasons/no season 2: 251;
- no cropland/no grassland: 254.
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).
For more information, please visit FAO GIEWS Earth Observation website at: https://www.fao.org/giews/earthobservation/index.jsp?lang=en
Data creation: 2018-01-01
Supplemental Information:
No data value: -9999
Citation:
Recommended citation: @ FAO - Agricultural Stress Index System (ASIS), http://www.fao.org/giews/earthobservation/, [Date accessed]
Contact points:
Resource Contact: Yanyun Li
Metadata Contact: Global Information and Early Warning System (GIEWS)
Data lineage:
DISCLAIMERS
The boundaries and names shown and the designations used on the maps do not imply the expression of any opinion whatsoever on the part of FAO concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers and boundaries.
Resource constraints:
Data license policy: Creative Commons Attribution- NonCommercial-ShareAlike 3.0 IGO (CC BY-NC- SA 3.0 IGO)
Online resources:
FAO DATASET
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ASIS: Crop/Pasture phenology (Growing season)