Suspended sediments and algal chlorophyll in surface water: An analysis of spectral radiance.

摘要

The quality of surface water is an important environmental concern. The two major optically active factors affecting water quality are suspended sediments and algal chlorophyll. The problem, from the standpoint of remote sensing, is that the two co-exist in nature, and one must somehow "disaggregate" the composite signal in order to measure amounts of each component.; This research focused on remote sensing for measuring amounts of algal chlorophyll in the presence of suspended sediments. Hyperspectral reflectivity from surface waters containing suspended sediment, algal chlorophyll, and mixtures of both were characterized. The absorption, transmission, and extinction of light in the water column for each case were summarized.; Large tanks and controlled experimental procedures were used to study the spectral responses from suspended sediments in clear water and also algal chlorophyll in clear water. Next, experiments were conducted involving the interaction of the two components. Finally, the findings from the tanks were evaluated with regard to data acquired on a large, turbid reservoir.; Controlled experiments elucidated the best wavelengths for measuring sediments. The relationship between suspended sediments and reflectance were linear at low concentrations but non-linear at high concentrations. Subtle shifts in wavelengths of peak reflectance were documented for varying suspended sediment concentrations and also for changing algal-chlorophyll amounts. Both a near-infrared/red ratio and the first derivative of reflectance proved useful for measuring chlorophyll concentrations. The additive effects of suspended sediments on reflectance from algae-laden water occurred at wavelengths between 400 and 900 nm, but the magnitude of the effect was not equal at all wavelengths. The near-infrared/red ratio was useful for measuring chlorophyll concentrations in the presence of suspended sediments, but the first derivative of reflectance was slightly better. The responses of PAR absorption and transmittance to variable suspended sediment concentration were exponential.; The findings from the reservoir were similar to those achieved in the tank experiments. The results of this research suggest that algal-chlorophyll concentration can be measured in the presence of suspended sediments.