通过优化劈窗算法,建立适合长江口水域的海表温度反演模型,利用2000年至2012年的Terra-MODIS LIB晴空数据进行海表温度反演,得到长江口13年海表温度数据集,分析长江流域进入河口的水沙变化后河口水域海表温度的年际变化和季节性变化.结果表明:长江口海表温度主要受太阳辐射影响,温度场的空间分布由口内至外海呈现阶梯性变化.受海域潮流上溯和径流下泄的影响,口内口外的海表温度表现出不同的季节性变化特征:冬季,口外高口内低;夏季,则口外低,口内高.伴随着冬季流域进入河口的径流量增加,长江口口外海域的冬季海表温度也出现下降趋势.

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 L1B 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.