Assessing Water Clarity and Trophic Condition of the Bight of Bangkok with Satellite Remote Sensing Imagery

要旨

Eutrophication caused by excessive inputs of nutrients is the most common impairment of surface waters. Traditional water quality assessment techniques are costly and time-consuming, often resulting in sporadic sampling over time and space. With this study we test the applicability and accuracy of satellite-based water clarity/trophic condition assessment methods developed for inland lakes in temperate zones over the tropical zone, the Bight of Bangkok, in the Gulf of Thailand. The secondary objectives are to examine the comparability of Thematic Mapper sensor with the Enhanced Thematic Mapper Plus sensor, and to investigate the accuracy improvement by using surface radiance values instead of raw digital numbers. Results showed that the accuracy of water clarity/trophic state prediction using the satellite data was quite high (r2 values 0.779 -- 0.899; p < 0.001). The r2 from the two sensors were not significantly different, indicating that this method can be used with both sensors. The difference of r2 results between digital numbers and radiance values were not substantial; however, the r2 of radiance values improved slightly. We argue that satellite image data and the presented model provide a cost effective and accurate method for water quality assessment and monitoring on a regional scale in tropical environments.