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| Titel |
Estimation of the spatial validity of local aerosol measurements in Europe using MODIS data |
| VerfasserIn |
Carlos Marcos, J. Luis Gómez-Amo, Roberto Pedrós, M. Pilar Utrillas, J. Antonio Martínez-Lozano |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076869
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| Zusammenfassung |
| The actual impact of atmospheric aerosols in the Earth’s radiative budget is still associated to
large uncertainties [IPCC, 2007]. Global monitoring of the aerosol properties and distribution
in the atmosphere is needed to improve our knowledge of climate change. The
instrumentation used for this purpose can be divided into two main groups: ground-based and
satellite-based. Ground-based instruments, like lidars or Sun-photometers, are usually
designed to measure accurate local properties of atmospheric aerosols throughout the day.
However, the spatial validity of these measurements is conditioned by the aerosol variability
within the atmosphere. Satellite-based sensors offer spatially resolved information about
aerosols at a global scale, but generally with a worse temporal resolution and in a less
detailed way.
In this work, the aerosol optical depth (AOD) at 550nm from MODIS Aqua,
product MYD04 [Remer, 2005], is used to estimate the area of validity of local
measurements at different reference points, corresponding to the AERONET [Holben,
1998] stations during the 2011-2012 period in Europe. For each case, the local AOD
(AODloc) at each reference point is calculated as the averaged MODIS data within a
radius of 15 km. Then, the AODloc is compared to the AOD obtained when a larger
averaging radius is used (AOD(r)), up to 500 km. Only those cases where more
than 50% of the pixels in each averaging area contain valid data are used. Four
factors that could affect the spatial variability of aerosols are studied: proximity
to the sea, human activity, aerosol load and geographical location (latitude and
longitude).
For the 76 reference points studied, which are sited in different regions of Europe, we
have determined that the root mean squared difference (RMSD) between AODloc and AOD(r)
, averaged for all cases, increases in a logarithmic way with the averaging radius (RMSD -
log(r)), while the linear correlation coefficient (R) decreases following a logarithmic trend (R
- -log(r)). Among all the factors studied, the aerosol load is the most influential one in the
aerosol spatial variability: for averaging radii smaller than 40 km, the RMSD increases with
AODloc. Another important factor is the latitude and longitude: the variation of the RMSD in
the AOD with regard to the averaging radius can differ up to a 60%, depending on the
location. On the contray, the proximity to the sea and the amount of population surrounding
each reference point do not have a noticeable influence compared to the above mentioned
factors.
Holben, B. N., Eck, T. F., Slutsker, I., Buis, J. P., Setzer, A., Vermote, E., Reagan, J. A.,
Kaufman, Y., Nakajima, T., Lavenu, F., and Smirnov, A.: AERONET – A federated
instrument network and data archive for aerosol characterization, Remote Sens. Environ., 66,
1–16, 1998.
IPCC (2007). S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.
Tignor, H.L. Miller (Eds.), Climate Change 2007: The Physical Science Basis. Contribution
of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel
on Climate Change. Cambridge University Press, Cambridge, UK & New York,
USA.
Remer, L. A., y co-authors, 2005: The MODIS aerosol algorithm, products, and
validation. J. Atmos. Sci., 62, 947–973. doi: http://dx.doi.org/10.1175/JAS3385.1 |
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