Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trends
We 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. Along-track and across-track sampling strategies are employed, in which the full MODIS data...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2014-07-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/7/2313/2014/amt-7-2313-2014.pdf |
| _version_ | 1818839723207032832 |
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| author | P. R. Colarco R. A. Kahn L. A. Remer R. C. Levy |
| author_facet | P. R. Colarco R. A. Kahn L. A. Remer R. C. Levy |
| author_sort | P. R. Colarco |
| collection | DOAJ |
| description | We 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. Along-track and
across-track sampling strategies are employed, in which the full MODIS
data set is sub-sampled with various narrow-swath (~ 400–800 km) and
single pixel width (~ 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°) 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°) 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-of-atmosphere aerosol radiative forcing
of 2–3 W m<sup>−2</sup>. 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. |
| first_indexed | 2024-12-19T03:58:49Z |
| format | Article |
| id | doaj.art-8e4ffc7ee2d7418a82249fdffdf405fd |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-19T03:58:49Z |
| publishDate | 2014-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-8e4ffc7ee2d7418a82249fdffdf405fd2022-12-21T20:36:45ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482014-07-01772313233510.5194/amt-7-2313-2014Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trendsP. R. Colarco0R. A. Kahn1L. A. Remer2R. C. Levy3Atmospheric Chemistry and Dynamics Laboratory (Code 614), NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAClimate and Radiation Laboratory (Code 613), NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAJoint Center for Earth Systems Technology, University of Maryland-Baltimore County, 5523 Research Park Dr., Suite 320, Baltimore, MD 21250, USAClimate and Radiation Laboratory (Code 613), NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAWe 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. Along-track and across-track sampling strategies are employed, in which the full MODIS data set is sub-sampled with various narrow-swath (~ 400–800 km) and single pixel width (~ 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°) 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°) 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-of-atmosphere aerosol radiative forcing of 2–3 W m<sup>−2</sup>. 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.http://www.atmos-meas-tech.net/7/2313/2014/amt-7-2313-2014.pdf |
| spellingShingle | P. R. Colarco R. A. Kahn L. A. Remer R. C. Levy Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trends Atmospheric Measurement Techniques |
| title | Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trends |
| title_full | Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trends |
| title_fullStr | Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trends |
| title_full_unstemmed | Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trends |
| title_short | Impact of satellite viewing-swath width on global and regional aerosol optical thickness statistics and trends |
| title_sort | impact of satellite viewing swath width on global and regional aerosol optical thickness statistics and trends |
| url | http://www.atmos-meas-tech.net/7/2313/2014/amt-7-2313-2014.pdf |
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