Poster Session 3, Wednesday,  October  5, 16:00–18:00

Poster 71

Estimating of the lake trophic state index in tropical region using surface hyperspectral reflectance: a case study of lakes in Northern Vietnam

Assessing and monitoring the lake trophic level is critical for any lake management program. Monitoring the lake’s trophic state using remote sensing is still challenged due to the complexity of the lake’s optical properties along with the eutrophication process. In this study, we proposed two band-ratio algorithms for estimating the Carlson’s trophic state index (TSI) using a dataset of 300 in situ point data of water surface reflectance, R w (l), concentrations of chlorophyll-a, total phosphorus, and water transparency (SD) measured simultaneously in ten lakes in Northern Vietnam. The trophic levels of study lakes range from mesotrophy to hypertrophy, with TSI varying widely from 35 to 95. SD was considered as the primary limiting factor for increasing productivity in the study lakes and higher TSI. Results demonstrates a strong correlation of TSI with reflectance within 750-770 nm (R 2 = 0.69) and the appropriateness of the near-infrared/green spectral ratio, R w (750-770)/R w (540-570) for estimating TSI (R 2 = 0.73; RMSE = 2.18). A combination of the ratio with reflectance in the blue region, [R w (750-770)-R w (470-490)]/R w (540-570) provides better TSS estimations on a large scale when applying to spectral bands of Landsat OLI and Sentinel MSI (R 2 > 0.82; RMSE < 3). Adding data from oligotrophic lakes to complete the range of TSI in the algorithm must be our plan in the future.

Ha Nguyen, Vietnam National University, Hanoi, [email protected], 0000-0002-5010-5615

Quang Vinh Pham, Institute of Geography, Vietnam Academy of Science and Technology, Hanoi, Vietnam, [email protected]

Thao Nguyen Thien Phuong, Faculty of Geology, University of Science, Vietnam National University, Hanoi, Vietnam, [email protected]

Linh Nguyen Thuy, Faculty of Geology, University of Science, Vietnam National University, Hanoi, Vietnam, [email protected]

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