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| Titel |
Effect of spectrally varying albedo of vegetation surfaces on shortwave radiation fluxes and aerosol direct radiative forcing |
| VerfasserIn |
L. Zhu, J. V. Martins, H. Yu |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 5, no. 12 ; Nr. 5, no. 12 (2012-12-12), S.3055-3067 |
| Datensatznummer |
250003211
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| Publikation (Nr.) |
 copernicus.org/amt-5-3055-2012.pdf |
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| Zusammenfassung |
This study develops an algorithm for representing detailed spectral features
of vegetation albedo based on Moderate Resolution Imaging Spectrometer
(MODIS) observations at 7 discrete channels, referred to as the MODIS
Enhanced Vegetation Albedo (MEVA) algorithm. The MEVA algorithm empirically
fills spectral gaps around the vegetation red edge near 0.7 μm and
vegetation water absorption features at 1.48 and 1.92 μm which cannot
be adequately captured by the MODIS 7 channels. We then assess the effects
of applying MEVA in comparison to four other traditional approaches to
calculate solar fluxes and aerosol direct radiative forcing (DRF) at the top
of atmosphere (TOA) based on the MODIS discrete reflectance bands. By
comparing the DRF results obtained through the MEVA method with the results
obtained through the other four traditional approaches, we show that filling
the spectral gap of the MODIS measurements around 0.7 μm based on the
general spectral behavior of healthy green vegetation leads to significant
improvement in the instantaneous aerosol DRF at TOA (up to 3.02 W m−2
difference or 48% fraction of the aerosol DRF, −6.28 W m−2,
calculated for high spectral resolution surface reflectance from 0.3 to 2.5 μm
for deciduous vegetation surface). The corrections of the spectral
gaps in the vegetation spectrum in the near infrared, again missed by the
MODIS reflectances, also contributes to improving TOA DRF calculations but
to a much lower extent (less than 0.27 W m−2, or about 4% of the
instantaneous DRF).
Compared to traditional approaches, MEVA also improves the accuracy of the
outgoing solar flux between 0.3 to 2.5 μm at TOA by over 60 W m−2
(for aspen 3 surface) and aerosol DRF by over 10 W m−2 (for dry grass).
Specifically, for Amazon vegetation types, MEVA can improve the accuracy of
daily averaged aerosol radiative forcing in the spectral range of 0.3 to
2.5 μm at equator at the equinox by 3.7 W m−2. These improvements
indicate that MEVA can contribute to regional climate studies over vegetated
areas and can help to improve remote sensing-based studies of climate
processes and climate change. |
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