Application of the geostationary ocean color imager (GOCI) to mapping the diurnal and seasonal variability of surface suspended matter in a macro-tidal estuary

摘要

Total suspended particulate matter (TSM) in estuarine and coastal regions usually exhibits significant diurnal and seasonal variability. The understanding of such variability can reveal the sedimentary processes in coastal turbid waters which play a central role in the water quality and primary productivity in the ocean. The aim of this study is to investigate the diurnal and seasonal variabilities of surface TSM distribution and its mechanisms in the Yalu River Estuary (YRE), Liaoning, China. Data from field measurements and polar-orbiting satellites with coarse spatial and limited temporal resolution are insufficient for monitoring surface TSM distribution in coastal waters. The Geostationary Ocean Color Imager (GOCI), the world's first geostationary ocean color satellite sensor, however, provides measurements over northeast Asia at hourly intervals. With regard to diurnal variability, there were usually two peaks of TSM in a tidal cycle corresponding to the maximum flood and ebb current. Tidal action appears to play a vital role in diurnal variability of TSM. Both the processes of tidal re-suspension and advection could be identified; however, the diurnal variability of TSM was mainly affected by a re-suspension process. In addition, special attention was paid to the effect of spring-neap tidal cycle on the TSM diurnal distribution. Scenarios under different daily tidal ranges implied that spring-neap tides can affect both the TSM values and the magnitude of TSM diurnal variability in the YRE: higher TSM concentrations with great fluctuation occurred during spring tide and TSM values were lower during neap tide with limited fluctuation.The GOCI-retrieved TSM results in the YRE showed a clearly seasonal variability of surface TSM during observation period, with the highest level in winter and the lowest in summer. A comparison between TSM results in the wet and dry seasons demonstrated that TSM concentrations were significantly higher in the dry season although river discharge was much greater in the wet season than the dry season. The seasonal variability of river discharge can only affect the TSM in the inner estuary during a flooding event. Seasonal action of wind waves was considered to be the main factor affecting TSM seasonal variability in the YRE.