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| Titel |
Characterizing spatiotemporal patterns in time series of the remotely sensed Fraction of Absorbed Photosynthetically Active Radiation |
| VerfasserIn |
L. Fürst, M. D. Mahecha, H. Lange, M. Jung, M. Reichstein, N. Gobron, M. Hauhs |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026886
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| Zusammenfassung |
| The CO2 uptake of the terrestrial biosphere (Gross Primary Productivity, GPP) plays a key
role in the global carbon balance. This carbon flux cannot be determined directly on a global
scale. Yet, the remotely sensed Fraction of Absorbed Photosynthetically Active Radiation
(FAPAR) is a valuable proxy for GPP. This study aims at characterizing global
FAPAR dynamics on different temporal scales and extracting corresponding spatial
structures. The time series were analyzed to uncover the presence and extent of
trends, and to identify quasi-oscillatory patterns from intra- to interannual time
scales.
Eight years of FAPAR data derived from the Sea-viewing Wide Field-of-view Sensor
(SeaWiFS) from 1998 to 2005 at a 0.5-Ã 0.5- latitude/longitude grid and 10 days temporal
resolution were investigated globally. In addition, the analysis was applied consistently to the
bi-monthly Normalized Difference Vegetation Index (NDVI) sampled by the Advanced Very
High Resolution Radiometer (AVHRR) available since 1981, as well as to ancillary climate
variables; for the latter, we used the CRU-PIK climate data, originating from the global
climate grid of the Climatic Research Unit (CRU). The overarching dominance of the
annual cycle was removed by deseasonalizing the time series using Singular System
Analysis. Spectral analysis was based on the Lomb-Scargle periodogram to extract
the spectral power at each scale. Trend detection was performed by means of the
nonparametric Mann-Kendall test. An advantage of all methods is their ability to handle
short, noisy, and fragmented time series, which typically applies to remote sensing
data.
The retrieved patterns of relative spectral power from monthly to interannual time scales
in FAPAR data are spatially coherent and largely consistent with that of NDVI. By using
temperature and precipitation data we identify regions where the scale-wise FAPAR behavior
is closely related to climate dynamics. The coincidence of significant trends in
FAPAR and NDVI suggest a recent ’browning’ tendency in several areas. This can be
attributed to a continuous rise in temperature and alterations of the hydrological
cycle.
Overall, the study suggests that the FAPAR dynamics exhibits characteristic spatial
patterns on different temporal scales that emerge from a complex interplay of corresponding
fluctuations in temperature and precipitation. However, we can also find examples where
FAPAR dynamics cannot be traced back to climate and is apparently shaped by other
geo-ecological drivers. |
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