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| Titel |
The Collection 6 MODIS aerosol products over land and ocean |
| VerfasserIn |
R. C. Levy, S. Mattoo, L. A. Munchak, L. A. Remer, A. M. Sayer, F. Patadia, N. C. Hsu |
| 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 ; 6, no. 11 ; Nr. 6, no. 11 (2013-11-06), S.2989-3034 |
| Datensatznummer |
250085103
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| Publikation (Nr.) |
 copernicus.org/amt-6-2989-2013.pdf |
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| Zusammenfassung |
| The twin Moderate resolution Imaging Spectroradiometer (MODIS) sensors have
been flying on Terra since 2000 and Aqua since 2002, creating an extensive
data set of global Earth observations. Here, we introduce the Collection 6
(C6) algorithm to retrieve aerosol optical depth (AOD) and aerosol size
parameters from MODIS-observed spectral reflectance. While not a major
overhaul from the previous Collection 5 (C5) version, there are enough
changes that there are significant impacts to the products and their
interpretation. The C6 aerosol data set will be created from three separate
retrieval algorithms that operate over different surface types. These are
the two "Dark Target" (DT) algorithms for retrieving (1) over ocean (dark
in visible and longer wavelengths) and (2) over vegetated/dark-soiled land
(dark in the visible), plus the "Deep Blue" (DB) algorithm developed
originally for retrieving (3) over desert/arid land (bright in the visible).
Here, we focus on DT-ocean and DT-land (#1 and #2). We have updated
assumptions for central wavelengths, Rayleigh optical depths and gas
(H2O, O3, CO2, etc.) absorption corrections, while relaxing
the solar zenith angle limit (up to ≤ 84°) to increase
poleward coverage. For DT-land, we have updated the cloud mask to allow
heavy smoke retrievals, fine-tuned the assignments for aerosol type as
function of season/location, corrected bugs in the Quality Assurance (QA)
logic, and added diagnostic parameters such topographic altitude. For
DT-ocean, improvements include a revised cloud mask for thin-cirrus
detection, inclusion of wind speed dependence on the surface reflectance,
updates to logic of QA Confidence flag (QAC) assignment, and additions of
important diagnostic information. At the same time, we quantified how
"upstream" changes to instrument calibration, land/sea masking and cloud
masking will also impact the statistics of global AOD, and affect Terra and
Aqua differently. For Aqua, all changes will result in reduced global AOD
(by 0.02) over ocean and increased AOD (by 0.02) over land, along with
changes in spatial coverage. We compared preliminary data to surface-based
sun photometer data, and show that C6 should improve upon C5. C6 will include
a merged DT/DB product over semi-arid land surfaces for reduced-gap coverage
and better visualization, and new information about clouds in the aerosol
field. Responding to the needs of the air quality community, in addition to
the standard 10 km product, C6 will include a global (DT-land and DT-ocean)
aerosol product at 3 km resolution. |
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