Effects of molecular and particle scatterings on the model parameter for remote-sensing reflectance

摘要

For optically deep waters, remote-sensing reflectance (r_(rs)) is traditionally expressed as the ratio of the backscattering coefficient (b_(b)) to the sum of absorption and backscattering coefficients (a+b_(b)) that multiples a model parameter (g, or the so-called f′/Q). Parameter g is further expressed as a function of b_(b)/(a+b_(b)) (or b_(b)/a) to account for its variation that is due to multiple scattering. With such an approach, the same g value will be derived for different a and b_(b) values that provide the same ratio. Because g is partially a measure of the angular distribution of upwelling light, and the angular distribution from molecular scattering is quite different from that of particle scattering; g values are expected to vary with different scattering distributions even if the b_(b)/a ratios are the same. In this study, after numerically demonstrating the effects of molecular and particle scatterings on the values of g, an innovative r_(rs) model is developed. This new model expresses r_(rs) in two separate terms: one governed by the phase function of molecular scattering and one governed by the phase function of particle scattering, with a model parameter introduced for each term. In this way the phase function effects from molecular and particle scatterings are explicitly separated and accounted for. This new model provides an analytical tool to understand and quantify the phase-function effects on r_(rs), and a platform to calculate r_(rs) spectrum quickly and accurately that is required for remote-sensing applications.