Retrieval of sea surface salinity with MERIS and MODIS data in the Bohai Sea

A simple multi-linear regression model was developed for sea surface salinity, and tested against in situ measurements. The algorithm can be applied to in situ measured reflectance data with a root mean square error of 0.833 psu (R2 = 0.64). The model was recalibrated based on remote sensing reflectance data derived from MERIS and from in situ salinity data, yielding a RMSE in modeled salinity (relative to in situ data) of 1.311 psu. This recalibrated model can be applied to MODIS data following a linear correction. The spatio-temporal changes in sea surface salinity and in the influence of freshwater flow were analyzed using MERIS, MODIS and river discharge data. Sea surface salinity in Laizhou Bay, Bohai Bay and Liaodong Bay was fresher than that in Qinhuangdao, the central Bohai Sea and Bohai Strait. During 2004-2009, the temporal trends in sea surface salinity varied between sites. Salinity in most parts of the Bohai Sea was increasing. The Yellow River discharge was found to have the greatest influence on sea surface salinity near the river estuary, whereas it had only a weak impact on the salinity far from river mouth. More independent datasets are needed to improve the model and to gain a better understanding of processes controlling changes in sea surface salinity.