Estimation of underwater visibility from satellite ocean color data

The present work aims to investigate spatial/temporal fluctuations of vertical visibility namely Secchi disk depth (Z_sd) using ocean colour remote sensing data. The Secchi depth (Z_sd) obtained for clear and turbid coastal waters in the region of Point Calimere (located at east coast of Southern India) is estimated through the semi-empirical approach which is based on the the remote sensing reflectance band ratio (R_rs(443/555). This study demonstrates a strong positive correlation between the band ratio R_rs(443/555) and the independent parameters of length attenuation coefficient (1/(c+K_d)), which positively governs the rate at which Coupling Coefficient (Γ) varies under a given illumination condition and hence, the Secchi transparency. The proper parameterization of beam attenuation coefficient c(m^-1) and spectral diffuse attenuation coefficient K_d(m^-1) is achieved at 531nm through the band ratio technique to capture the effect of the maximum light penetration. Moreover, the secondary parameter which governs the rate at which penetration of light occurs is modeled as the function of reflectance at 551nm (R_rs551). The modeled Secchi Depth (Z_sd) is found to be in good agreement with the measured values with significantly low errors and high slope and correlation coefficient.