Modeling the effects of near-surface plumes of suspended particulate matter on remote-sensing reflectance of coastal waters.

A radiative transfer model was applied to examine the effects of vertically stratified inherent optical properties of the water column associated with near-surface plumes of suspended particulate matter on spectral remote-sensing reflectance, R(rs)(λ), of coastal marine environments. The simulations for nonuniform ocean consisting of two layers with different concentrations of suspended particulate matter (SPM) are compared with simulations for a reference homogeneous ocean whose SPM is identical to the surface SPM of the two-layer cases. The near-surface plumes of particles are shown to exert significant influence on R(rs)(λ). The sensitivity of R(rs)(λ) to vertical profile of SPM is dependent on the optical beam attenuation coefficient within the top layer, c(1)(λ), thickness of the top layer, z(1), and the ratio of SPM in the underlying layer to that in the top layer, SPM(2)/SPM(1), as well as the wavelength of light, λ. We defined a dimensionless spectral parameter, P(λ)=c(1)(λ)×z(1)×(SPM(2)/SPM(1)), to quantify and examine the effects of these characteristics of the two-layer profile of SPM on the magnitude and spectral shape of R(rs)(λ). In general, the difference of R(rs)(λ) between the two-layer and uniform ocean decreases to zero with an increase in P(λ). For the interpretation of ocean color measurements of water column influenced by near-surface plumes of particles, another dimensionless parameter P'(λ) was introduced, which is a product of terms representing homogenous ocean and a change caused by the two-layer structure of SPM. Based on the analysis of this parameter, we found that for the two-layer ocean there is a good relationship between R(rs)(λ) in the red and near-infrared spectral regions and the parameters describing the SPM(z) profile, i.e., SPM(1), SPM(2), and z(1).