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The Sensitivity of SeaWiFS Ocean Color Retrievals to Aerosol Amount and TypeAs atmospheric reflectance dominates top-of-the-atmosphere radiance over ocean, atmospheric correction is a critical component of ocean color retrievals. This paper explores the operational Sea-viewing Wide Field-of-View Sensor (SeaWiFS) algorithm atmospheric correction with approximately 13 000 coincident surface-based aerosol measurements. Aerosol optical depth at 440 nm (AOD(sub 440)) is overestimated for AOD below approximately 0.1-0.15 and is increasingly underestimated at higher AOD; also, single-scattering albedo (SSA) appears overestimated when the actual value less than approximately 0.96.AOD(sub 440) and its spectral slope tend to be overestimated preferentially for coarse-mode particles. Sensitivity analysis shows that changes in these factors lead to systematic differences in derived ocean water-leaving reflectance (Rrs) at 440 nm. The standard SeaWiFS algorithm compensates for AOD anomalies in the presence of nonabsorbing, medium-size-dominated aerosols. However, at low AOD and with absorbing aerosols, in situ observations and previous case studies demonstrate that retrieved Rrs is sensitive to spectral AOD and possibly also SSA anomalies. Stratifying the dataset by aerosol-type proxies shows the dependence of the AOD anomaly and resulting Rrs patterns on aerosol type, though the correlation with the SSA anomaly is too subtle to be quantified with these data. Retrieved chlorophyll-a concentrations (Chl) are affected in a complex way by Rrs differences, and these effects occur preferentially at high and low Chl values. Absorbing aerosol effects are likely to be most important over biologically productive waters near coasts and along major aerosol transport pathways. These results suggest that future ocean color spacecraft missions aiming to cover the range of naturally occurring and anthropogenic aerosols, especially at wavelengths shorter than 440 nm, will require better aerosol amount and type constraints.
Document ID
20160010651
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Kahn, Ralph A.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Sayer, Andrew M.
(Universities Space Research Association Greenbelt, MD, United States)
Ahmad, Ziauddin
(Science and Data Systems, Inc. Silver Spring, MD, United States)
Franz, Bryan A.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
August 30, 2016
Publication Date
May 27, 2016
Publication Information
Publication: Journal of Atmospheric & Oceanic Technology
Publisher: American Meteorological Society
Volume: 33
Issue: 6
e-ISSN: 1520-0426
Subject Category
Earth Resources And Remote Sensing
Report/Patent Number
GSFC-E-DAA-TN35098
Funding Number(s)
CONTRACT_GRANT: NNG14HZ03C
CONTRACT_GRANT: NNG11HP16A
Distribution Limits
Public
Copyright
Other
Keywords
single scattering albedo
aerosol optical depth
SeaWiFS

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