基于卫星雷达测高技术的湖库动态监测理论、方法和研究进展

Monitoring lakes and reservoirs using satellite radar altimetry:Theory,methods,and progresses

水位是反映水体变化的重要变量,利用卫星测高技术获取湖库的水位信息,很大程度上改变了传统地面观测数据匮乏的现状。本文综述了卫星雷达测高技术在湖泊和水库动态监测方面的理论、主要的数据处理方法和数据产品,以及当前的主要研究进展。从文献检索可以看出,当前的应用研究对象主要聚焦在个别湖泊或小范围内的湖泊群;在数据处理方面,数据以单一测高任务数据为主,并依赖于主流数据库的三级产品,针对一级、二级产品的数据处理方法研究较少;在研究主题方面,主要以湖库水位变化趋势及影响因素分析为主,也有少量研究聚焦在水量估算、流域水文模拟等方向。未来发展新的数据处理方法,如全聚焦SAR技术和干涉宽刈幅数据处理技术等,研发新的测高任务(如测高小卫星星簇计划SMASH、地表水和海洋地形SWOT、以及欧盟的下一代测高任务Sentinel-3 NGT等),来提高中小型湖库的测高数据精度、覆盖范围以及频率,将为测高研究带来新的机遇。

Water level is an important variable that indicates the variations in the vertical dimension of inland water bodies.However,insitu monitoring of water level of lakes and reservoirs is expensive.Thus,the coverage of gauging network is relatively low.The satellite altimetry technology,originally used for ocean research,has been widely applied for inland water research on a local to regional and global scale.As the success of several altimetry missions,the situation of data scarcity has been mitigated,especially in the recent decade.The literature review shows that the mainstream of altimetry research for lakes and reservoirs focuses on one specific or few lakes/reservoirs aiming at a detailed investigation.Regarding the altimetry data sets,most studies use high-level products(i.e.water level data instead of raw signals)from one certain database,such as Hydroweb,DAHITI,etc.,but very few exploit the low-level products.The major research foci include temporal variations of water level,and the attribution of water level changes in the context of climate changes.Besides,some publications research the water storage changes and thus assess the water resources and management issues,while some others focus on catchment hydrologic modeling with water levels of lakes/reservoirs as constraints.In this short review article,we first briefly introduced the theory of inland altimetry,followed by the descriptions of major freely openaccess products of different levels.Then,we summarized the common data processing procedures including data screening,waveform retracking,outlier removal,time series construction,etc.We intend to guide the newcomers to prepare data for their own studies of interest when dealing with low-level products if necessary.Moreover,we reviewed the latest progresses of inland water altimetry,especially for lakes and reservoirs research.The progresses are reported in three main directions,i.e.,water level monitoring and analysis,dynamics of water storage,and catchment hydrologic modeling.The latter two directions involve more data sets other than altimetry-derived water levels and still need more research for further advancement.We concluded this study with recommendations on future research topics,such as new data processing techniques(e.g.Fully-Focused SAR and Wide swath InSAR processing,Machine Learning,etc.)to extract water levels that are more accurate.We also provide introductions of several proposed or planed future altimetry missions(e.g.SWOT,Sentinel-3 Next Generation Topography,Sentinel-6-Next Generation,etc.)that will provide many opportunities for lake and reservoir research beyond just lake/reservoir monitoring.Moreover,we highlight the value of multi-mission(or constellations)data sets for high spatio-temporal resolution mapping of inland water bodies.Meanwhile,it is also very important to develop freely open-access high-level databases for end users,such as hydrological modelers.