Eutrophic status assessment using remote sensing data

Eutrophication is one of the most common problems of water resources in developed and developing countries. Traditional measurement of water quality requires on-site sampling and laboratory work, which is expensive and time consuming. Due to these imitations, the sample size is often too small to have a high reliability of the corresponding results especially for a large water body. Remote sensing provides a new technique to monitor water quality over a wide area with a two-dimensional data distribution instead of sample points. In this research, French satellite SPOT was chosen as remotely sensed data source and provided images to derive chlorophyll concentration, Secchi depth, and phosphorus concentration for a water body. By comparing a set of on-site samples and the corresponding brightness values on a SPOT image taken on the same date, a regression model converting satellite data to water quality variables was defined. A systematic image process was developed to transfer SPOT data to water quality variables. This system provides not only an instantaneous and repetitive eutrophic status assessment but also a visualizing water quality variation. An image process and GIS software IMAGINE was adopted to carry out the process in a case study of the Te-Chi Reservoir in Taiwan. The final product is a set of thematic maps of eutrophic status (represented by Carlson's TSI) of the reservoir.