Sea Surface Temperature（ SST） is an important parameter of the sea water environment

especially that of the Yangtze estuary. An accurate retrieval of SST is helpful in studying the hydrodynamic environment of estuaries and marine phenomena

such as upwelling and temperature fronts. Affected by both land runoff and ocean currents

estuarine water is strongly mixed

making it different from ocean water in terms of thermal infrared radiation properties and atmospheric conditions. Thus

the algorithm for ocean water is not tuned for estuarine water. The above issue is addressed in this study with the development of a new Yangtze Estuarine Sea Surface Temperature（ YESST） algorithm. The proposed algorithm was made applicable to estuarine environments by basing it on the Qin split-window algorithm and by optimizing its calculation of two key parameters

namely

atmospheric transmittance and sea surface emissivity. The YESST algorithm was applied to the Terra-MODIS L1 B data and validated with both in situ water temperature data and the standard MODIS SST product. In terms of bias and RMSE

analysis showed that the results of YESST algorithm have improved accuracy compared with the standard MODIS SST products. The bias was reduced by 0. 23 ℃

and RMSE was reduced by 0. 62 ℃. The YESST algorithm was used to retrieve the 13-year SST dataset（ 2000—2012） on the Yangtze estuarine waters

as well as 574 images. The SST spatial distribution and the seasonal and interannual SST variations in the research area were revealed according to the dataset. The SST of the Yangtze estuarine water presents a stepwise change spatially from the upstream to the lower reaches of the estuary

which is dominated by solar radiation. The SST outside the river mouth is higher than the SST in the inner estuary in winter; this condition is reversed in summer. On January 29

2007

for example

the SST of the research area ranged from 3 ℃ to 13 ℃. On July 29

2007

the SST was as high as 24 ℃ to 35 ℃. Meanwhile

the temperature gradient from the upstream to the lower reaches of the estuary is higher in winter than in summer. This result indicates that the SST of estuarine areas is the result of the interaction between land runoff and sea currents and that terrestrial water is a heat source in summer and a cold source in winter. In 2003

the Three Gorges Reservoir began regulating the Yangtze water discharge.The increased runoff in winter season

during which large amounts of cold water flow into the estuary

has more a significant cooling effect on the SST outside the river mouth than on the SST in the inner estuary

as determined from the daily SST data retrieved.However

decreased land runoff in the summer season when solar radiation plays a decisive role in the SST of estuarine waters does not obviously affect SST.