Atmospheric correction for NO₂ absorption in retrieving water-leaving reflectances from the SeaWiFS and MODIS measurements

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https://opg.optica.org/ao/fulltext.cfm?uri=ao-46-26-6504&id=141121

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https://doi.org/10.1364/AO.46.006504
 http://hdl.handle.net/11603/27787

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UMBC Joint Center for Earth Systems Technology (JCET)

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Author/Creator ORCID

https://orcid.org/0000-0002-9146-1632

Date

2007-09-05

Type of Work

journal articles
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Citation of Original Publication

Ahmad, Ziauddin, et al. "Atmospheric correction for NO₂ absorption in retrieving water-leaving reflectances from the SeaWiFS and MODIS measurements" APPLIED OPTICS 46, no. 26 (10 september 2007): 6504-6512. https://doi.org/10.1364/AO.46.006504.

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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract

The absorption by atmospheric nitrogen dioxide (NO₂ ) gas in the visible has been traditionally neglected in the retrieval of oceanic parameters from satellite measurements. Recent measurements of NO₂ from spaceborne sensors show that over the Eastern United States the NO₂ column amount often exceeds 1 Dobson Unit (∼2.69×10¹⁶ molecules/cm²) . Our radiative transfer sensitivity calculations show that under high NO₂ conditions (∼1×10¹⁶ molecules/cm²) the error in top-of-atmosphere (TOA) reflectance in the blue channels of the sea-viewing wide field-of-view sensor (SeaWiFS) and moderate-resolution imaging spectroradiometer (MODIS) sensors is approximately 1%. This translates into approximately 10% error in water-leaving radiance for clear waters and to higher values (>20%) in the coastal areas. We have developed an atmospheric-correction algorithm that allows an accurate retrieval of normalized water-leaving radiances (nLws) in the presence of NO₂ in the atmosphere. The application of the algorithm to 52 MODIS scenes over the Chesapeake Bay area show a decrease in the frequency of negative nLw estimates in the 412  nm band and an increase in the value of nLws in the same band. For the particular scene reported in this paper, the mean value of nLws in the 412 nm band increased by 17%, which is significant, because for the MODIS sensor the error in nLws attributable to the digitization error in the observed TOA reflectance over case 2 waters is ∼2 .5% .