Analysis on SSC of Fine-Grained Sediment Flocs by In Situ Spectral Characteristics in the Yangtze Estuary

In order to understand the distribution and changing process of fine-grained suspended sediment flocs at a large scale in the Yangtze Estuary, in situ irradiance reflectance and suspended sediment concentrations (SSC) of fine-grained sediment flocs in surface water (0.5 m) were monitored in the south channel of the Yangtze Estuary from May 23 to June 2 of 2009 by a spectroradiometer and water sample analysis, respectively. The relationship between SSC and spectral reflectivity of fine-grained sediment flocs was modeled. The results show that (1) Spectral reflectivity increased with increased SSC of fine-grained suspended sediment flocs. Two spectral reflectivity peaks exist in 690~720 nm and 810 nm band, respectively. (2) There existed fine relationship between SSC and spectral reflectivity. The correlations between SSC and spectral reflectivity with band larger than 715 nm were bigger than 0.7 with a confidence level of p<;0.01. (3) Exponential relationship was the best one between SSC and single-band spectral reflectivity, and power function relationship was also the best one between SSC and multi-band spectral reflectivity ratio. Among the five chosen single-bands, the r of wavelength at 860 nm is the best with a value of 0.86. And the power regression of 860/670 spectral reflectance ratio is the best one among the four empirical relationships using four ratios whit r=0.89.