Crop/Pasture Phenology is a reference dataset used by ASIS.
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.
Compliment to ASIS Crop/pasture growing seasons (Start of season, Maximum of season and End of Season) maps, Progress of Season (POS) maps depict 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, represented by a value between 0 and 100 percent (i.e. 50 percent is the mid-point of the growing season). The seasons’ progress is based on the long-term average 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.
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).
The definition of a dekad:
- Each month has three dekads: dekad 1 (day 1-10), dekad 2 (day 11-20), dekad 3 (day 21-end of month).
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The number of days the dekad represents is variable for each last dekad of the month.
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Since the phenology is derived from dekadal temporally smoothed and gap filled NDVI data, these dekads represent +- the middle day of their period.
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The best practice is to link each dekad value with its associated date (e.g. Dekad 1 = January 5th/6th, dekad 3 = January 26th,…). Then you can convert these dates into Julian days.
Phenology digital values to physical values:
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In order to deal with growing seasons surpassing the calendar year (e.g. SOS <January or EOS > December) the phenology data is stored in a range of 108 dekads. The digital values in images follow the 1-108 dekad range. There is an offset of 36 dekads in order to express them with the target year as reference.
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Dekad 37-72 represents the dekad 1-36 (January – December) of the target year. Values lower than 36 indicate SOS phenology < January and values higher than 72 indicate EOS phenology > December.
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: 2014-01-01
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:
pro_C_21_s1.png
FAO DATASET
ASIS: Crop/Pasture phenology: Progress of Season
