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validation of long-term global aerosol climatology project optical thickness retrievals using aeronet and modis dataA comprehensive set of monthly mean aerosol optical thickness (AOT) data from coastal and island AErosol RObotic NETwork (AERONET) stations is used to evaluate Global Aerosol Climatology Project (GACP) retrievals for the period 1995-2009 during which contemporaneous GACP and AERONET data were available. To put the GACP performance in broader perspective, we also compare AERONET and MODerate resolution Imaging Spectroradiometer (MODIS) Aqua level-2 data for 2003-2009 using the same methodology. We find that a large mismatch in geographic coverage exists between the satellite and ground-based datasets, with very limited AERONET coverage of open-ocean areas. This is especially true of GACP because of the smaller number of AERONET stations at the early stages of the network development. Monthly mean AOTs from the two over-the-ocean satellite datasets are well-correlated with the ground-based values, the correlation coefficients being 0.81-0.85 for GACP and 0.74-0.79 for MODIS. Regression analyses demonstrate that the GACP mean AOTs are approximately 17%-27% lower than the AERONET values on average, while the MODIS mean AOTs are 5%-25% higher. The regression coefficients are highly dependent on the weighting assumptions (e.g., on the measure of aerosol variability) as well as on the set of AERONET stations used for comparison. Comparison of over-the-land and over-the-ocean MODIS monthly mean AOTs in the vicinity of coastal AERONET stations reveals a significant bias. This may indicate that aerosol amounts in coastal locations can differ significantly from those in adjacent open-ocean areas. Furthermore, the color of coastal waters and peculiarities of coastline meteorological conditions may introduce biases in the GACP AOT retrievals. We conclude that the GACP and MODIS over-the-ocean retrieval algorithms show similar ranges of discrepancy when compared to available coastal and island AERONET stations. The factors mentioned above may limit the performance of the validation procedure and cause us to caution against a direct extrapolation of the presented validation results to the entirety of the GACP dataset.
Document ID
20150023278
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Geogdzhayev, Igor V.
(Columbia Univ. New York, NY, United States)
Mishchenko, Michael I.
(NASA Goddard Inst. for Space Studies New York, NY United States)
Date Acquired
December 18, 2015
Publication Date
September 24, 2015
Publication Information
Publication: Remote Sensing
Volume: 7
Issue: 10
ISSN: 2072-4292
Subject Category
Meteorology and Climatology
Earth Resources and Remote Sensing
Report/Patent Number
GSFC-E-DAA-TN27168
Funding Number(s)
WBS: WBS 281945.02.03.03.27
CONTRACT_GRANT: NNX14AB99A
Distribution Limits
Public
Copyright
Other
Keywords
MODIS (radiometry)
Aerosols
Optical thickness
Imaging spectrometers