Remote sensing monitoring of the suspended particle size in Hongze Lake based on GF-1 data

In remote sensing analyses of water colour, suspended particle size is an important optical parameter that also plays an important role in inland and coastal biogeochemical processes. Knowledge of the suspended particle size and its changes in month and area can be used to assess the contributions by suspended particulate matter to backscatter coefficient, particle sinking, and carbon sequestration under lake water. In this study, in situ samples collected in the summer and winter from Hongze Lake (HZL), 2016, were used to develop an empirical model to estimate the median diameter (D_V⁵⁰) of suspended particle sizes. The spatial distributions of D_V⁵⁰ were derived using 37 WFV (Wide Field Viewer) images of GF-1 (GaoFen-1), China, and the fluctuational diversification and the potential influencing factors were discussed. Several crucial findings can be drawn: (1) the empirical band ratio algorithm R_rs,green: R_rs,red was suitable for D_V⁵⁰ estimation with a coefficient of determination (R²) of approximately 0.7 for the modelling data. In addition, the validation data showed that the MAPE (mean absolute percentage error) is below 34%, the RMSE (root mean square error) is less than 4.2 μm, and the Mean ratio is close to 1; (2) the average median particle size shows an increasing trend from the northeast of the lake (NE) to Chengzi Lake (CZL) and the wetland (WL) in HZL from 2015 to 2016; (3) the D_V⁵⁰ of HZL is higher in summer than in the other seasons during the study period; (4) the fluctuation in hydrological factors, especially the monthly water discharge and flow, might be the driving force behind the seasonal variations in D_V⁵⁰ of HZL; and (5) channel transportation reduced D_V⁵⁰, and the reduced amplitude might be more than 22%.