Abstract
Empirical band ratio algorithms for the estimation of colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) for Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Moderate Resolution Imaging Spectroradiometer (MODIS) and MERIS ocean color sensors were assessed and developed for the northern Gulf of Mexico. Match-ups between in situ measurements of CDOM absorption coefficients at 412 nm (aCDOM(412)) with that derived from SeaWiFS were examined using two previously reported reflectance band ratio algorithms. Results indicate better performance using the Rrs(510)/Rrs(555) (Bias = −0.045; RMSE = 0.23; SI = 0.49, and R2 = 0.66) than the Rrs(490)/Rrs(555) reflectance band ratio algorithm. Further, a comparison of aCDOM(412) retrievals using the Rrs(488)/Rrs(555) for MODIS and Rrs(510)/Rrs(560) for MERIS reflectance band ratios revealed better CDOM retrievals with MERIS data. Since DOC cannot be measured directly by remote sensors, CDOM as the colored component of DOC is utilized as a proxy to estimate DOC remotely. A seasonal relationship between CDOM and DOC was established for the summer and spring-winter with high correlation for both periods (R2~0.9). Seasonal band ratio empirical algorithms to estimate DOC were thus developed using the relationships between CDOM-Rrs and seasonal CDOM-DOC for SeaWiFS, MODIS and MERIS. Results of match-up comparisons revealed DOC estimates by both MODIS and MERIS to be relatively more accurate during summer time, while both of them underestimated DOC during spring-winter time. A better DOC estimate from MERIS in comparison to MODIS in spring-winter could be attributed to its similarity with the SeaWiFS band ratio CDOM algorithm.
Highlights
Dissolved organic matter (DOM), the largest bioreactive inventory of carbon in the global ocean comparable in size to the atmospheric CO2 stock has a major impact on the global carbon cycle and climate change [1,2]
The relationship between Chromophoric DOM (CDOM) and dissolved organic carbon (DOC), as well as an assessment of CDOM and DOC retrieval algorithms using Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Moderate Resolution Imaging Spectroradiometer (MODIS), and MERIS were addressed in this study
DOC obtained from different research cruises covering areas over the Louisiana shelf in 2005 and from 2007 to 2009 were employed to evaluate and develop CDOM and DOC retrieval algorithms
Summary
Dissolved organic matter (DOM), the largest bioreactive inventory of carbon in the global ocean comparable in size to the atmospheric CO2 stock has a major impact on the global carbon cycle and climate change [1,2]. The abundance of DOM has generally been determined as dissolved organic carbon (DOC), a major component of organic carbon [3]. Chromophoric DOM (CDOM), the colored component of DOM primarily absorbs light in the UV and visible spectral range affecting the intensity and spectral quality of the light field in the aquatic medium. DOC cannot be sensed directly by ocean color sensors; CDOM, the colored fraction of DOC, can be estimated remotely. CDOM can be utilized as an inexpensive intermediary to estimate the standing stock of DOC and the carbon cycle in aquatic environments. Coble [6] reported CDOM’s contribution to DOC ranged from
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