LAUSR

Monitoring chlorophyll-a concentration (Chl-a) in inland waters, particularly hypertrophic lake waters in megacities, is a critically important environmental issue. To enable long-term Chl-a monitoring using Landsat series sensors, development of a Chl-a estimation algorithm for the new Landsat sensor is requisite. This study aims to identify the most accurate algorithm for Chl-a estimation in hypertrophic waters using Landsat 8 images and in situ Chl-a data from West Lake and nine other hypertrophic lakes in Hanoi (Vietnam's capital). The best estimation was obtained by the ratio of two reflectances at 562 and 483 nm, corresponding to the ratio of the OLI band 3 versus band 2, termed the GrB2 algorithm. The GrB2 values using the reflectances of water samples and the Landsat images were correlated with the Chl-a by an exponential function (r2 = 0.64 to 0.82), and the estimated Chl-a were verified by the smallness of standard error (smaller than 10%) and degree of conformity with recent fish-kill phenomena that commonly occur in those lakes in summer and early spring. Because the availability of GrB2 is limited to waters with low levels of inorganic suspended matter, its extension to waters with much higher levels requires further investigation.