Retrieval Of Suspended Sediment Concentration In The Yangtze Estuary And Its Spatiotemporal Dynamics Analysis Based On GOCI Image Data

The Yangtze Estuary, which is located in the east of China, plays a major role in the ecosystem, fisheries and economic. However, it is often characterized by high concentrations of suspended sediment, which influences not only the water quality but also the geomorphologic evolution in the estuary area. What’s more, the concentration of sediment shows high diurnal dynamics. Therefore, real-time monitoring the spatiotemporal dynamics of suspended sediment concentration is of great significance.In order to meet the needs of spatial dynamics and diurnal cycle, Geostationary Ocean Color Imager(GOCI) data were used. Atmospheric correction which is aimed at removing the influence by the absorption and scattering of atmosphere is needed for GOCI data in order to get water leaving reflectance of the target. MODTRAN radiative transfer model was used for correction and several atmospheric correction schemes were set as inputs of the model. The results are water leaving reflectance maplist. Simultaneously, 2SeaColor forward model was utilized to simulate Rrs by setting up a series of suspended sediment concentrations(SSC). Then a matching method was applied pixel by pixel to find out the best atmospheric correction scheme as well as the corresponding SSC value for each pixel. Field data were used to validate the results. The correlation coefficient of Rrs is up to 0.81 and that of SSC is 0.68. It is obvius that the result of this research has a great improvement compared with other SSC products.We used the same method to process the images from different times on the same day, so simple analyses on the spatial dynamics and the diurnal cycle of SSC could be done. In the spatial domain, the study area can be divided into three regions according to different concentration values: high concentration region(up to 2000 mg/l), medium concentration region(with a sediment concentration range of 50 mg/l to 100 mg/l) and low concentration area(far from the coast, always with a concentration below 10 mg/l). In the temporal domain, our analysis could reveal the relationship between the diurnal variations of SSC and the tidal cycle in the area. There is a time lag between maximum turbidity and water level, SSC first decreases and then increases when the tide is rising. That is mainly due to the dilution effect of incoming sea water in the estuary and the resuspension of the benthic sediments.