The effect of particulate organic content on the remote sensing of marine suspended sediment

We report on the relationship between the backscattering coefficient at 665 nm and the cross sectional area of particles in suspension in the Irish Sea, Celtic Sea and English Channel. A plot of the backscattering coefficient against particle area shows two distinct trends: one for particles with high mineral content and another for particles with low mineral content. Backscattering per unit particle area (effective backscattering efficiency, Qbb) shows a continuous non-linear dependence on the ratio of mineral to total suspended solids (MSS/TSS) over the range 0.35 <MSS/TSS <0.91. The relationship can be represented by an exponential function: Qbb = 0.000087 exp(6.9 MSS/TSS), which explains 62% of the observed variance in backscattering efficiency. Changes in particle size have no significant influence on Qbb. As the MSS/TSS ratio increases, the backscattering ratio (bb/b) also increases. The implication for the quantitative remote sensing of marine suspended sediments is that the mass specific backscattering coefficient, bb* depends on the particle area per unit mass multiplied by a function which depends on the mineral content of the particles.