Monitoring inland water via Sentinel satellite constellation: A review and perspective

Abstract

Clean Water and Sanitation, the sixth goal of Sustainable Development Goals (SDGs 6) is a call for action by the United Nations aiming at balancing the water cycle for sustainable life on the earth. For water security and regional sustainable development, the quantity and quality of inland waters are key variables. Over the past decades, satellite remote sensing offers global information about inland water dynamics in a real-time and low-cost way. Amongst, the Sentinel satellites designed by the European Space Agency can provide global monitoring with a spatial resolution of up to 10 m and several days of revisit time. Although Sentinel satellites have been explored in inland water monitoring for a long time period, a systematical review on the research progress and challenges of their applications has not been documented well. This review aims to present a comprehensive review of the Sentinel satellites (especially for Sentinel-1, Sentinel-2, and Sentinel-3) in monitoring inland water, both on the quantity and quality dimensions, including the water extent, level, depth, volume and water quality (e.g., chlorophyll-a, phycocyanin, suspended particulate matter, colored dissolved organic matter, and Secchi disk depth). A total of 690 publications are involved and the bibliometric quantitative approach is used to analyze the areas in which Sentinel instrument excelled and their performance with different processing methods. The implications for virtual constellation construction using Sentinel satellites from different missions and the contribution of a virtual constellation in support of the SDG 6 are also discussed. According to the initial investigation and characteristics of various satellites, we have proposed several schemes for Sentinel virtual constellation toward different missions covering water quantity measurement and water quality monitoring, which can maximize the observation capability of the satellite. The optimal Sentinel virtual constellation constructing scheme theoretically enables a coverage of 10 m spatial resolution and less than 2 days temporal resolution for all-weather inland water monitoring. These solutions will significantly enhance the observational capacity to obtain high-quality, long-term water security parameters in supporting SDG 6. Nevertheless, there remains a scarcity of freely available Sentinel-derived products, widely applicable data processing algorithms, and unified platform, capable of supporting water security monitoring on a broad scale.