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| Titel |
Upscaling of evapotranspiration fluxes from instantaneous to daytime scales for thermal remote sensing applications |
| VerfasserIn |
C. Cammalleri, M. C. Anderson, W. P. Kustas |
| 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 ; 18, no. 5 ; Nr. 18, no. 5 (2014-05-22), S.1885-1894 |
| Datensatznummer |
250120364
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| Publikation (Nr.) |
 copernicus.org/hess-18-1885-2014.pdf |
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| Zusammenfassung |
| Four upscaling methods for estimating daytime actual evapotranspiration (ET)
from single time-of-day snapshots, as commonly retrieved using remote
sensing, were compared. These methods assume self-preservation of the ratio
between ET and a given reference variable over the daytime hours. The
analysis was performed using eddy covariance data collected at 12 AmeriFlux
towers, sampling a fairly wide range in climatic and land cover conditions.
The choice of energy budget closure method significantly impacted
performance using different scaling methodologies. Therefore, a statistical
evaluation approach was adopted to better account for the inherent
uncertainty in ET fluxes using eddy covariance technique. Overall, this
approach suggested that at-surface solar radiation was the most robust
reference variable amongst those tested, due to high accuracy of upscaled
fluxes and absence of systematic biases. Top-of-atmosphere irradiance was
also tested and proved to be reliable under near clear-sky conditions, but
tended to overestimate the observed daytime ET during cloudy days. Use of
reference ET as a scaling flux yielded higher bias than the solar radiation
method, although resulting errors showed similar lack of seasonal
dependence. Finally, the commonly used evaporative fraction method yielded
satisfactory results only in summer months, July and August, and tended to
underestimate the observations in the fall/winter seasons from November to
January at the flux sites studied. In general, the proposed methodology
clearly showed the added value of an intercomparison of different upscaling
methods under scenarios that account for the uncertainty in eddy covariance
flux measurements due to closure errors. |
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