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Impact of Satellite Viewing-Swath Width on Global and Regional Aerosol Optical Thickness Statistics and TrendsWe use the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite aerosol optical thickness (AOT) product to assess the impact of reduced swath width on global and regional AOT statistics and trends. Alongtrack and across-track sampling strategies are employed, in which the full MODIS data set is sub-sampled with various narrow-swath (approximately 400-800 km) and single pixel width (approximately 10 km) configurations. Although view-angle artifacts in the MODIS AOT retrieval confound direct comparisons between averages derived from different sub-samples, careful analysis shows that with many portions of the Earth essentially unobserved, spatial sampling introduces uncertainty in the derived seasonal-regional mean AOT. These AOT spatial sampling artifacts comprise up to 60%of the full-swath AOT value under moderate aerosol loading, and can be as large as 0.1 in some regions under high aerosol loading. Compared to full-swath observations, narrower swath and single pixel width sampling exhibits a reduced ability to detect AOT trends with statistical significance. On the other hand, estimates of the global, annual mean AOT do not vary significantly from the full-swath values as spatial sampling is reduced. Aggregation of the MODIS data at coarse grid scales (10 deg) shows consistency in the aerosol trends across sampling strategies, with increased statistical confidence, but quantitative errors in the derived trends are found even for the full-swath data when compared to high spatial resolution (0.5 deg) aggregations. Using results of a model-derived aerosol reanalysis, we find consistency in our conclusions about a seasonal-regional spatial sampling artifact in AOT Furthermore, the model shows that reduced spatial sampling can amount to uncertainty in computed shortwave top-ofatmosphere aerosol radiative forcing of 2-3 W m(sup−2). These artifacts are lower bounds, as possibly other unconsidered sampling strategies would perform less well. These results suggest that future aerosol satellite missions having significantly less than full-swath viewing are unlikely to sample the true AOT distribution well enough to obtain the statistics needed to reduce uncertainty in aerosol direct forcing of climate.
Document ID
20150000202
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.5194/amt-7-2313-2014
Authors
Colarco, P. R. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Kahn, R. A. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Remer, L. A. (Maryland Univ. Baltimore, MD, United States)
Levy, R. C. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
January 6, 2015
Publication Date
July 31, 2014
Publication Information
Publication: Atmospheric Measurement Techniques-Discussions
Publisher: Copernicus Publications
Volume: 7
Issue: 7
Subject Category
Geosciences (General)
Report/Patent Number
GSFC-E-DAA-TN11429
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
remote sensing
aerosols
climate

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