Estimation of chlorophyll-a concentration in Lake Erhai based on OLCI data

Ocean and land colour instrument(OLCI) is a new ocean colour remote sensor mounted on Sentinel-3, and its applicability to water quality monitoring of inland clean water is to be verified. Chlorophyll-a (Chl.a) concentration is an important water quality parameter for measuring the eutrophication of Lake Erhai. Based on the in-situ samples taken from April 19, 2017, the performance of three Chl.a estimation models (including Band-Ratio Model, Three-Band Model and FLH Model) was evaluated in this study and the spatial distribution of Chl.a concentrations in Lake Erhai was estimated. The results showed that: (1) The Three-Band Model by Oa8, Oa11 and Oa12 was most suitable for the estimation of Chl.a concentration in Lake Erhai, the mean absolute percent error was 12.37%, lower than the Band-Ratio Model(16.04%) and FLH Model(13.50%); (2) Among atmospheric correction methods for OLCI, the application of the dark pixel method based on the rayleigh-scattering correction was better than that of the 6S, FLAASH and QUAC methods; (3) The near shore water pixels in the OLCI image of Lake Erhai were affected seriously by the land adjacency effect, and the distance of the land adjacency effect at the near-infrared band (Oa12) was 1~2 pixels while the Oa8, Oa10 and Oa11 bands were 1 pixel; (4) On April 19, 2017, the average Chl.a concentration of the whole Lake Erhai was 12.15±5.72 μg/L with the lowest in the middle waters (9.00-12.00 μg/L) and the highest in the northern waters (12.00-22.76 μg/L). Although the Chl.a concentration of the southern waters (12.00-14.00 μg/L) was a little higher than that of the middle waters, the lowest concentration in the estuary of the Yangnan River and the Boluo River was around 8.33 μg/L due to the River Plume" caused by rainfall. © 2018 by Journal of Lake Sciences."