New era for satellite-based water monitoring
The WorldWater project is pioneering cutting-edge satellite technology and algorithms to facilitate smart resource management by
mapping surface water bodies from the sky. As the project reaches the halfway mark, GWI checks in on its progress so far.
The end of 2021 marked the conclusion of the first phase of the WorldWater project, which brings the water sector a big step closer to embracing a new and improved technique of satellite-based sur-face water monitoring. As part of phase one of the project funded by the European Space Agency, extensive method evalu-ations compiling data from 15 high per-forming algorithms applying either (or both) optical and radar satellite data were undertaken across five distinct pilot areas: Colombia, Mexico, Zambia, Gabon and Greenland. Together, the project partners (DHI, GISAT, GeoVille, GRID-Arendal and the Danish Technological University) have now produced prototype software which is set to solve the challenges that exist with current monitoring methods.
Climate change, increasing populations and changes in land use, such as growing urbanisation and deforestation, are all rap-idly driving the need to be able to better understand surface water dynamics. The targets set by the United Nations under Sustainable Development Goal 6 (SDG6) in relation to freshwater ecosystems also make accurate surface water monitoring increasingly vital. Christian Tøttrup, pro-ject lead at the WorldWater project and sen-ior project manager at DHI, explained how this project was instigated “with a key aim of trying to empower national or regional stakeholders with satellite data and tools to better monitor their inland water resources and improve water resource management.”
Traditionally, monitoring of surface water dynamics has been done using in-situ stations (for example, using level meas-urements) or imagery obtained from opti-cal Landsat satellites. The data obtained from Landsat satellites enables imagery to be produced to a resolution of 30 by 30 metres. However, as Tøttrup points out “studies have found that around 10% of the world’s surface water area is actually within the resolving power of these 30 by 30 metres. These water bodies which you
cannot see at that scale can have significant ecological and management implications.” Newer and better data from the Sentinel missions of the European Union Coperni-cus initiative is now available, and enables a resolution of down to 10 by 10 metres. Until now, this data had not yet been used to its full potential in the water sector.
The conclusions from the WorldWater study demonstrated that while using a sin-gle sensor approach (applying either optical or radar satellite data) can provide compre-hensive results for very specific localities, a dual sensor approach (combining data from both optical and radar satellites) is the most effective way to undertake large-scale surface water mapping. “If you really want to do large area mapping, and where you’re covering large gradients of bio-climatic regions, then the dual sensor approach is really the most consistent and the most robust way,” Tøttrup told GWI.
Up to now, a dual-sensor approach has not been widely adopted for surface water monitoring due to limitations in available data. However, the partners in this project have created new algorithms and work-flows using the most up-to-date data from both optical and radar satellites. These will provide more comprehensive surface water mapping than has ever been done before. Importantly, the project will also demon-strate how changes in surface water vol-ume can be monitored over selected water bodies by combining surface water extent maps with water level timeseries obtained from satellite altimetry missions.
While the two-year project began in May 2020, it has been subject to delays due to the pandemic. The project is now mov-ing into the implementation phase, which involves building out the software and analytics portal, transferring this to users and building up capacity. The WorldWater project will be working with national stake-holders in its pilot countries to implement use cases, showing how the new informa-tion that they have processed can help to improve decision making. Particular atten-tion will be paid to how the new tools can support better national resource planning, SDG reporting, and natural disaster and climate change management, including the identification of glacial lake outbursts, and flood and drought risk mitigation.
Seeing the bigger picture
WorldWater is piloting across diverse locations to generate comprehensive satellite image analysis and tools, which can be used to improve water body management and boost resilience to climate-related risks.