Detecting the Zambezi River plume using observed optical properties

In April 1998 a research cruise was carried out in the Mozambique Channel t aking detailed optical, water quality and salinity measurements; the Zambez i plume waters were apparent through strong colour fronts with green waters in the plume and clear blue waters offshore. A good (r(2) = 0.76) negative empirical relationship was found between the salinity (S) and yellow subst ance, represented by the absorption of filtered samples at 440 nm (g440). A n empirical relationship was found between the salinity and a reflectance r atio: S(1/2Z(sd)) = 37.45-7.07 (R555/R490) An optical model in which light absorption is dominated by yellow substance and light scattering by inorganic particles confirms this empirical relati onship. This has been applied to a SeaWIFS image to map salinity on the Sof ala Bank, demonstrating the potential to remotely determine the distributio n of the Zambezi River plume. It is thought that any significant level of c hlorophyll would reduce the effectiveness of the above algorithm. (C) 2001 Elsevier Science Ltd. All rights reserved.