The spectral responses of algal chlorophyll in water with varying levels of suspended sediment

Abstract

The purpose of this paper is to investigate the spectral responses of algal chlorophyll and water, under natural sunlight with varying suspended sediment concentrations (SSC). Twenty levels of SSC with each of two sediment types were generated, ranging from 50 to 1000 mgl⁻¹, in 75101 of water containing chlorophyll-a concentrations of 718 μgl⁻¹ and 295 μgl⁻¹. Results indicate that suspended sediments do not eliminate the prominent spectral patterns of algal chlorophyll, even as SSC reached 1000 mgl⁻¹. Between 400 and 900 nm, the relation between reflectance and SSC satisfies the expression: d²R(λ)/dS²<0. The effects of varying SSC on the positions and magnitudes of pronounced chlorophyll features were investigated. The ratio between the NIR and red wavelengths was totally independent of SSC. Thus, our finding supports using it as an index for measuring chlorophyll in natural surface water containing suspended sediments.