SWOT's new satellite technology provides unprecedented global monitoring of water levels, aiding resource management in large watersheds such as the Ohio River. By providing detailed and frequent data, SWOT improves the ability of researchers and managers to more accurately understand and predict water resource availability.
The Ohio River Basin, a vast network of reservoirs, lakes, and rivers stretching from Pennsylvania to Illinois, has a drainage area nearly the size of France. This region of more than 25 million people is now being monitored with unprecedented precision thanks to the SWOT (Surface Water and Ocean Topography) mission, a joint effort between NASA and CNES.
Since early 2023, the SWOT satellite has been measuring the height of nearly all bodies of water on the Earth's surface, including oceans, lakes, reservoirs and rivers, achieving global coverage at least once every 21 days. In addition to the height of water, SWOT also tracks the horizontal distribution of water in freshwater bodies. Earlier this year, the mission began sharing its validated data with the public, opening up new possibilities for global water monitoring and management.
"Having both perspectives of water extent and water level, and covering large areas in detail and frequently, is unprecedented," said Jida Wang, a hydrologist at the University of Illinois at Urbana-Champaign and a member of the SWOT science team. "It is also a groundbreaking and exciting aspect of SWOT."
Researchers can use the mission's data on water levels and water extents to calculate how the storage capacity of a lake or reservoir changes over time. This in turn gives hydrologists a more precise understanding of a river's discharge - how much water flows through a particular stretch of river.
The visualization at the top of this article uses SWOT data from July 2023 to November 2024 to show average water levels above sea level in lakes and reservoirs in the Ohio River Basin (which flows into the Mississippi River).
Yellow indicates water levels above 1,600 feet (500 meters), and dark purple indicates water levels below 330 feet (100 meters). Comparing changes in these water levels can help hydrologists measure water availability locally or throughout a watershed over time.
Estimating freshwater availability to communities within a watershed has long been a challenge. Researchers gather information through water gauges installed in some lakes and reservoirs, airborne surveys, and other satellites that observe water levels or extents. However, the coverage of ground-based and airborne instruments is limited both in space and time. Hydrologists can piece together some of the data they need from different satellites, but the data may or may not have been collected at the same time, or researchers may still need to supplement the information with measurements from ground-based sensors.
Even so, calculating freshwater supplies is a complex undertaking. Much of the work relies on computer models. "Traditional water models often don't work well in highly regulated watersheds like the Ohio River because they struggle to represent the unpredictability of dam operations," said George Allen, a freshwater researcher at Virginia Tech in Blacksburg and a member of the SWOT science team.
Many river basins in the United States have dams and reservoirs that are jointly managed by multiple entities. While those who manage reservoirs may know the water quality conditions of the waters they manage, planning water supplies for entire rivers is difficult. Because SWOT focuses on both rivers and lakes, its data helps provide a more unified perspective.
"This data allows water managers to really understand what others in these freshwater systems are doing," said Colin Gleason, a hydrologist at the University of Massachusetts Amherst and a member of the SWOT science team.
While SWOT researchers are excited about the possibilities the data brings, there is still much work to be done. Satellite's high-resolution observations of water levels and water extents mean researchers have to wade through a vast sea of data, and processing and analyzing these measurements also takes some time.
The SWOT (Surface Water and Ocean Topography) satellite is a groundbreaking collaboration led by NASA and CNES, with important contributions from the Canadian Space Agency (CSA) and the UK Space Agency. The SWOT satellite, managed by NASA's Jet Propulsion Laboratory in partnership with the California Institute of Technology, is designed to measure global water levels and water body extents, providing valuable data for hydrology, climate science and water resources management.
NASA provided critical flight system components, including the Ka-band radar interferometer (KaRIn), GPS science receivers, laser retroreflectors, dual-beam microwave radiometers, and instrument operations infrastructure. CNES, in collaboration with Thales Alenia Space and the UK Space Agency, provided the satellite platform, ground operations and instruments such as the dual-frequency Poseidon altimeter, the Doppler Orbital Imaging and Satellite Radiation Positioning Integrated System (DORIS) and the KaRIn radio frequency subsystem. CSA played an important role by supplying KaRIn high-power transmitter components. Together, these contributions make SWOT a powerful tool for advancing our understanding of Earth's freshwater and ocean systems.
Compiled from /scitechdaily