SPECTRAL REFLECTANCE WITH VARYING SUSPENDED SEDIMENT CONCENTRATIONS IN CLEAR AND ALGAE-LADEN WATERS

The objective of the study was to characterize and compare the relatio nship between suspended sediment concentration (SCC) and reflectance i n clear and algae-laden wafers. A controlled experiment was conducted outdoors in a 7510-litre wafer tank using natural sunlight. A red loam soil was added and suspended in the tank filled with clear and algae- laden waters, respectively. A total of 20 levels of SSC (from 25 to 50 0 mg l(-1)) were created for each type of treatment. Reflectance was r ecorded using an ASD spectroradiometer, and the bi-directional reflect ance factor was computed and analyzed. The same amount of suspended se diment generated higher reflectance between 400 and 700 nm in clear wa ter than in algae-laden water due to the blue and red absorption of ch lorophyll. The effect of chlorophyll on the SSC-reflectance relationsh ip was minimum at wavelengths between 700 and 900 nm. For both clear a nd algae-laden wafers, the linearity in the SSC-reflectance relationsh ip increased with wavelength between 400 and 900 nm. A near-linear rel ationship between SSC and reflectance was found between 720 and 900 nm .