Using Sentinel-2B Imagery to Estimate the Eutrophication Level of Linh Dam Lake, Hoang Mai District, Hanoi

The successfully launched of Sentinel-2B (S2B) satellite into orbit created the recording frequency on Earth every 5 days with the simulated operating of Sentinel 2A satellite, and provided a high resolution (10m). This study aims to assess the effective application of S2B satellite on water environmental monitoring by using Secchi Disk Depth (SD) and surface water reflectance data, which was collected at the same time of the acquiring local scenes from S2B to establish SD estimated equation of Lake Linh Dam. Result showed that an accurate estimation model for SD in Lake Linh Dam by an exponential function of band 3 versus band 4 ratio (R2 = 0.86, RMSE=1.7). Resultant maps of SD distribution over the lake in 2018 and 2019 show that the water quality in Lake Linh Dam reached from the high eutrophication to super eutrophication level. This result is consistent with previous studies on eutrophication state of Lake Linh Dam, confirming the potential application of S2B image for water quality research in Hanoi lakes.

IDENTIFYING THE EUTROPHICATION STATUS OF SHALLOW WATERS BASED ON THE ESTIMATED TROPHIC STATE INDEX FROM SATELLITE DATA

Remote sensing techniques have been widely used to measure the qualitative parameters of waterbodies. This work identifies the eutrophication status of 6 small and shallow lakes, including Hoan Kiem, Ba Mau, Bay Mau, Dam Tri, Truc Bach and Hai Ba Trung, in the Hanoiurban area using an empirical model developed from the in situ trophic state index (TSI) and Landsat 8 satellite data acquired on 21 September 2016 and 10 December 2016. The strong correlation between TSI values and the reflectance ratio of Landsat 8 band 3 versus band 2 (R2 = 0.69) allowed the quantification of the TSI by an exponential function (MSE = 0.04). Validation of the model for other water samples collected on the dates shows a high accuracy (R2 = 0.85; MSE = 0.4). Maps of TSI over the 6 lakes on the two dates surveyed clarified the eutrophication status of these lakes in autumn 2016 and demonstrate the trend in identifying the distribution of TSI from space. Study methods and data stated in this study confirm the high applicability of Landsat 8 satellite data for monitoring shallow lake eutrophication status.