Optical Scattering Cross Sections for Suspended Organic and Mineral Matter in Coastal Waters of the Gulf of Mexico: Variance and Significance of Organic Scattering Cross Sections

Robert H Stavn, University of North Carolina Greensboro, Greensboro, NC, United States; Stennis Space Center, Visiting Scientist, Code 7330, Oceanography Division, Naval Research Laboratory, Stennis Space Center, United States, Alexander U Falster, Maine Mineral and Gem Museum, Bethel, ME, United States, Nicole Stockley, Florida Atlantic University, Harbor Branch Oceanographic Institute, Fort Pierce, FL, United States, Deric Gray, US Naval Research Laboratory, Washington, DC, United States and Richard W Gould Jr, US Naval Research Laboratory, Stennis Space Center, MS, United States
Abstract:
The Naval Research Laboratory, Stennis Space Center, MS USA along with the Harbor Branch Oceanographic Institute, Ft. Pierce, FL, USA conducted an extensive survey in March 2016 of the northern Gulf of Mexico entitled Characterizing Optical Layers with Combined Active and Passive Sensors. We gravimetrically characterized suspended organic matter (Particulate Organic Matter, POM) and suspended mineral matter (Particulate Inorganic Matter, PIM) along with concurrent observations of the absorption and scattering coefficients of the hydrosol. From these data we calculated the spectral mass-specific scattering cross sections of POM and PIM. These true optical properties are critical to generating reliable and accurate remote sensing algorithms, especially for the coastal region. The mass-specific scattering cross sections of PIM were comparable in Mobile Bay, Alabama, USA and the near shore Gulf of Mexico indicating the riverine supply. However, the mass-specific scattering cross sections of POM were quite different in Mobile Bay and the Gulf of Mexico, reported here for the first time. The spectral slope of the POM in Mobile Bay is apparently a power law proceeding from blue to red. The spectral slope for POM in the Gulf of Mexico showed significant troughs at the blue and red ends of the spectrum. Apparently POM in Mobile Bay is predominantly detrital in nature while POM in the Gulf of Mexico is predominantly living phytoplankton cells. These varying optical properties of the suspended matter, true optical scattering coefficients, call into question the use of a single empirical optical coefficient, or specific scattering coefficient, in generating remote sensing algorithms to estimate the suspended matter of the coastal ocean.
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