Regional optical algorithms linking apparent and inherent optical properties with upwelled subsurface water radiances (Lu) have been developed for ocean color satellites in Gulf of Mexico coastal waters. The algorithms were developed using a suite of optical measurements made in April 1993 at 28 stations in three regions of the northern Gulf of Mexico: off the Atchafalaya Basin, the Mississippi River Delta region, and the northwest Florida Shelf. These areas characterize different scattering and absorbing optical environments associated with river discharge areas. In addition to CTD profiles along offshore transects from Case II to Case I waters, optical profiles of spectral irradiance, up and downwelling irradiance, beam attenuation, fluorescence, and forward scattering were also made. These measurements have been incorporated into a data base of in situ optical parameters.
A strong relationship between the diffuse attenuation coefficient (K) and the beam attenuation coefficient (c) was observed for these waters. These optical properties are related to the spectral water-leaving radiances and form the foundation for branching algorithms for coastal ocean color. Deviations from the historical K vs Lu relationship developed by Austin & Petzold (1981) were observed in waters with K values exceeding 0.4 m-1. The stations were separated into three classes based on the value of K, and patterns in Lu vs. wavelength were examined. As K increases, water- leaving radiances in the 530-550 nm wavelength range increase, and at K values greater than 0.4 the maximum water-leaving radiance shifts to approximately 570 nm.