Using sea surface salinity (SSS) observation from the soil moisture active passive (SMAP) mission, we analyzed the spatial distribution and seasonal variation of SSS around Changjiang River (Yangtze River) Estuary for the period of September 2015 to August 2018. First, we found that the SSS from SMAP is more accurate than soil moisture and ocean salinity (SMOS) mission observation when comparing with the in situ observations. Then, the SSS signature of the Changjiang River freshwater was analyzed using SMAP data and the river discharge data from the Datong hydrological station. The results show that the SSS around the Changjiang River Estuary is significantly lower than that of the open ocean, and shows significant seasonal variation. The minimum value of SSS appears in July and maximum SSS in December. The root mean square difference of daily SSS between SMAP observation and in situ observation is around 3 in both summer and winter, which is much lower than the annual range of SSS variation. In summer, the diffusion direction of the Changjiang River freshwater depicted by SSS from SMAP is consistent with the path of freshwater from in situ observation, suggesting that SMAP observation may be used in coastal seas in monitoring the diffusion and advection of freshwater discharge.

中文翻译：

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长江口土壤水分主动被动海表盐度观测的验证与应用

利用从土壤水分主动（SMAP）任务观测到的海表盐度（SSS），我们分析了长江（长江）河口2015年9月至2018年8月期间SSS的空间分布和季节变化。发现与原位比较时，SMAP中的SSS比土壤湿度和海洋盐度（SMOS）任务观测更准确观察。然后，利用SMAP数据和大同水文站的河流流量数据分析了长江淡水的SSS特征。结果表明，长江口周围的SSS明显低于公海，并且具有明显的季节变化。SSS的最小值出现在7月，SSS的最大值出现在12月。在夏季和冬季，SMAP观测和原位观测之间每日SSS的均方根差约为3，远低于SSS年度变化范围。夏季，SMAP SSS描述的长江淡水扩散方向与原位淡水路径一致。 观测表明，SMAP观测可用于沿海海域，以监测淡水排放的扩散和对流。