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| Titel |
SACRA – a method for the estimation of global high-resolution crop calendars from a satellite-sensed NDVI |
| VerfasserIn |
S. Kotsuki, K. Tanaka |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 19, no. 11 ; Nr. 19, no. 11 (2015-11-05), S.4441-4461 |
| Datensatznummer |
250120843
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| Publikation (Nr.) |
 copernicus.org/hess-19-4441-2015.pdf |
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| Zusammenfassung |
| To date, many studies have performed numerical estimations of biomass
production and agricultural water demand to understand the present and future
supply–demand relationship. A crop calendar (CC), which defines the date or
month when farmers sow and harvest crops, is an essential input for the
numerical estimations. This study aims to present a new global data set, the
SAtellite-derived CRop calendar for Agricultural simulations (SACRA), and to
discuss advantages and disadvantages compared to existing census-based and
model-derived products. We estimate global CC at a spatial resolution of
5 arcmin using satellite-sensed normalized difference vegetation
index (NDVI) data, which corresponds to vegetation vitality and senescence on the land
surface. Using the time series of the NDVI averaged from three consecutive
years (2004–2006), sowing/harvesting dates are estimated for six crops
(temperate-wheat, snow-wheat, maize, rice, soybean and cotton). We assume
time series of the NDVI represent the phenology of one dominant crop and
estimate CCs of the dominant crop in each grid. The dominant crops are
determined using harvested areas based on census-based data. The cultivation
period of SACRA is identified from the time series of the NDVI; therefore,
SACRA considers current effects of human decisions and natural disasters. The
difference between the estimated sowing dates and other existing products is
less than 2 months (< 62 days) in most of the areas. A major
disadvantage of our method is that the mixture of several crops in a grid is
not considered in SACRA. The assumption of one dominant crop in each grid is
a major source of discrepancy in crop calendars between SACRA and other
products. The disadvantages of our approach may be reduced with future
improvements based on finer satellite sensors and crop-type classification
studies to consider several dominant crops in each grid. The comparison of
the CC also demonstrates that identification of wheat type (sowing in spring
or fall) is a major source of error in global CC estimations. |
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