Assessing CDOM from VIIRS satellite ocean color data in an estuarine environment – initial results from Apalachicola Bay

The VIIRS ocean color sensor on board the Suomi NPP satellite provides higher spatial resolution (~750 m) in comparison to the more established MODIS sensors on Aqua and Terra satellites, making it an attractive option for monitoring water quality in estuarine environments. Apalachicola Bay, an estuarine system located in the Northern Gulf of Mexico, is strongly influenced by the Apalachicola and Carrabelle Rivers, receiving high levels of dissolved organic matter (DOM) from their watersheds in Florida and Georgia. However, very little is known about the source and distribution of DOM and its optically-active colored component (CDOM) in this estuarine system. In-situ measurements of CDOM absorption in conjunction with temperature, salinity and remote sensing reflectance (Rrs) obtained during a field campaign in Apalachicola Bay in March 2015 were used to examine the spatial distribution of CDOM in relation to physical properties and to develop a CDOM algorithm for the VIIRS imagery. Following the application of an atmospheric-correction scheme to the VIIRS top-of-atmosphere reflectance for the Apalachicola Bay, satellite- and field-derived Rrs showed good similarity (R²=0.95); further, a test of different band combinations revealed a green to red band ratio to be well correlated to CDOM absorption at 412 nm (a_g412; R²=0.82, N=13). A VIIRS-derived CDOM map indicated a fairly reasonable representation of CDOM with high a_g412 in the vicinity of the Apalachicola and Carrabelle River plumes and low a_g412 in the area between two rivers and in the shelf waters. Although the empirical relationship lacked sufficient sample size and seasonality, preliminary results indicate the potential of using VIIRS data to monitor CDOM in estuarine environments.