Satellite retrieval of important ocean hydrological parameters:an overview

The ocean, which covers 71 percent of the Earth's surface, is a fundamental component of the global water cycle. Accurately monitoring the spatial and temporal dynamics of ocean hydro-physical parameters is important for comprehensive understanding of the global water cycle and the effective management of ocean water resources. Ocean remote sensing is a new and advanced space-based technique for estimating spatio-temporally distributed hydro-physical parameters. With five-decades of aerospace satellite sensors development, remote sensing approaches to retrieving ocean hydro-physical parameters appear mature. This paper briefly describes the principles of and retrieval algorithms for the main ocean hydro-physical parameters of Sea Surface Height(SSH), Sea Depth(SD), Sea Surface Current(SSC) and Water Volume Variation(WVV) using optical, passive-microwave and active-microwave remote sensing or combinations thereof. For each ocean hydro-physical parameter, the deficiencies of a single satellite sensor algorithm can be alleviated with the combined use of multi-sensors. Additionally, with the improvement of retrieval techniques, several regional and global hydro-physical parameter datasets have been generated. Hence, this paper also briefly describes the main datasets and their applications. Furthermore, to improve the retrieval accuracy of each hydro-physical parameter, the combination of observations from different sensors is a promising approach. As a result of international efforts, several new satellites are also scheduled to be launched into space, for example, the joint CNES-NASA satellite project SWOT(launch date in 2020) and China's second space lab, Tiangong-2(launch date in 2016). These satellites will greatly improve our ability to monitor the spatial and temporal dynamics of ocean hydro-physical parameters.