Assessing chlorophyll-a and turbidity in the Hartbeespoort Dam (South Africa) using Landsat imagery

摘要: The water quality of global inland lakes is deteriorating as a result of various anthropogenic influences. Addressing this problem requires accurate monitoring programmes. Traditional water quality assessments rely on sample-based in-situ observations that are expensive, timeconsuming and labour-intensive. In contrast, remote sensing based approaches overcome most of the problems inherent in traditional methods, and have shown a great potential in the estimation of water quality parameters. Most studies however utilised coarse spatial resolution data in an effort to cover wide spatial areas. Inland lake systems, by contrast, have received limited attention. Inland lakes exhibit relatively large localised variations of water quality, compared to large water-bodies such as the oceans. Such water-bodies therefore require assessments at an appropriate level of detail. The objective of this study was to evaluate the utility of individual spectral bands, Normalised Difference Vegetation Index (NDVI) and Normalised Difference Water Index (NDWI) of Landsat imagery in characterising chlorophylla concentrations and turbidity of the Hartbeespoort Dam, South Africa. Ordinary least-square regression analysis was used to relate field observed chlorophyll-a concentrations and turbidity with remotely sensed data. Chlorophyll-a concentrations were best estimated using NDVI (R2= 0.91; RMSE= 0.67), while the best correlation for turbidity was observed with NDWI (R2= 0.60; RMSE= 3.44). The study demonstrated that moderate resolution satellite imagery provides an empirical method of retrieving information on the status and dynamics of water quality for …