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| Titel |
Evaluating nighttime CALIOP 0.532 μm aerosol optical depth and extinction coefficient retrievals |
| VerfasserIn |
J. R. Campbell, J. L. Tackett, J. S. Reid, J. Zhang, C. A. Curtis, E. J. Hyer, W. R. Sessions, D. L. Westphal, J. M. Prospero, E. J. Welton, A. H. Omar, M. A. Vaughan, D. M. Winker |
| 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. 9 ; Nr. 5, no. 9 (2012-09-05), S.2143-2160 |
| Datensatznummer |
250003082
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| Publikation (Nr.) |
 copernicus.org/amt-5-2143-2012.pdf |
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| Zusammenfassung |
| NASA Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) Version 3.01
5-km nighttime 0.532 μm aerosol optical depth (AOD) datasets from
2007 are screened, averaged and evaluated at
1° × 1°
resolution versus corresponding/co-incident 0.550 μm AOD derived
using the US Navy Aerosol Analysis and Prediction System (NAAPS), featuring two-dimensional variational assimilation of
quality-assured NASA Moderate Resolution Imaging Spectroradiometer (MODIS)
and Multi-angle Imaging Spectroradiometer (MISR) AOD. In the absence of
sunlight, since passive radiometric AOD retrievals rely overwhelmingly on
scattered radiances, the model represents one of the few practical global estimates
available from which to attempt such a validation. Daytime comparisons,
though, provide useful context. Regional-mean CALIOP vertical profiles
of night/day 0.532 μm extinction coefficient are compared with
0.523/0.532 μm ground-based lidar measurements to investigate
representativeness and diurnal variability. In this analysis, mean nighttime
CALIOP AOD are mostly lower than daytime (0.121 vs. 0.126 for all aggregated
data points, and 0.099 vs. 0.102 when averaged globally per normalised
1° × 1° bin), though the relationship is reversed over
land and coastal regions when the data are averaged per normalised bin
(0.134/0.108 vs. 0140/0.112, respectively). Offsets assessed within single
bins alone approach ±20%. CALIOP AOD, both day and night, are
higher than NAAPS over land (0.137 vs. 0.124) and equal over water (0.082
vs. 0.083) when averaged globally per normalised bin. However, for all data
points inclusive, NAAPS exceeds CALIOP over land, coast and ocean, both day
and night. Again, differences assessed within single bins approach 50% in
extreme cases. Correlation between CALIOP and NAAPS AOD is comparable during
both day and night. Higher correlation is found nearest the equator, both as
a function of sample size and relative signal magnitudes inherent at these
latitudes. Root mean square deviation between CALIOP and NAAPS varies
between 0.1 and 0.3 globally during both day/night. Averaging of CALIOP
along-track AOD data points within a single NAAPS grid bin improves
correlation and RMSD, though day/night and land/ocean biases persist and are
believed systematic. Vertical profiles of extinction coefficient derived in
the Caribbean compare well with ground-based lidar observations, though
potentially anomalous selection of a priori lidar ratios for CALIOP retrievals is
likely inducing some discrepancies. Mean effective aerosol layer top heights
are stable between day and night, indicating consistent layer-identification
diurnally, which is noteworthy considering the potential limiting effects of
ambient solar noise during day. |
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