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.
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