SWOT’s new satellite technology offers unprecedented global monitoring of water levels, aiding in the management of resources in large basins like the Ohio River.
By providing detailed and frequent data, SWOT enhances the ability of researchers and managers to understand and predict water availability more accurately.
Revolutionizing Water Monitoring with SWOT Technology
The Ohio River Basin, spanning from Pennsylvania to Illinois, is a vast network of reservoirs, lakes, and rivers that drains an area nearly the size of France. This region, home to over 25 million people, is now being monitored with unprecedented precision thanks to the SWOT (Surface Water and Ocean Topography) mission, a joint effort by NASA and the French space agency CNES (Centre National d’Études Spatiales).
Since early 2023, the SWOT satellite has been measuring the height of almost all water on Earth’s surface — including oceans, lakes, reservoirs, and rivers — with global coverage achieved at least once every 21 days. In addition to water height, SWOT tracks the horizontal spread of water in freshwater bodies. Earlier this year, the mission began sharing its validated data with the public, opening new possibilities for global water monitoring and management.
New Perspectives on Water Levels and Storage
“Having these two perspectives — water extent and levels — at the same time, along with detailed, frequent coverage over large areas, is unprecedented,” said Jida Wang, a hydrologist at the University of Illinois Urbana-Champaign and a member of the SWOT science team. “This is a groundbreaking, exciting aspect of SWOT.”
Researchers can use the mission’s data on water level and extent to calculate how the amount of water stored in a lake or reservoir changes over time. This, in turn, can give hydrologists a more precise picture of river discharge — how much water moves through a particular stretch of river.
Visualizing Water Levels Across the Basin
The visualization at the top of this article uses SWOT data from July 2023 to November 2024 to show the average water level above sea level in lakes and reservoirs in the Ohio River Basin, which drains into the Mississippi River.
Yellow indicates values greater than 1,600 feet (500 meters), and dark purple represents water levels less than 330 feet (100 meters). Comparing how such levels change can help hydrologists measure water availability over time in a local area or across a watershed.
Overcoming Traditional Data Challenges
Historically, estimating freshwater availability for communities within a river basin has been challenging. Researchers gather information from gauges installed at certain lakes and reservoirs, from airborne surveys, and from other satellites that look at either water level or extent. But for ground-based and airborne instruments, the coverage can be limited in space and time. Hydrologists can piece together some of what they need from different satellites, but the data may or may not have been taken at the same time, or the researchers might still need to augment the information with measurements from ground-based sensors.
Even then, calculating freshwater availability can be complicated. Much of the work relies on computer models. “Traditional water models often don’t work very well in highly regulated basins like the Ohio because they have trouble representing the unpredictable behavior of dam operations,” said George Allen, a freshwater researcher at Virginia Tech in Blacksburg and a member of the SWOT science team.
SWOT’s Role in Unified Water Management
Many river basins in the United States include dams and reservoirs managed by a patchwork of entities. While the people who manage a reservoir may know how their section of water behaves, planning for water availability down the entire length of a river can be a challenge. Since SWOT looks at both rivers and lakes, its data can help provide a more unified view.
“The data lets water managers really know what other people in these freshwater systems are doing,” said SWOT science team member Colin Gleason, a hydrologist at the University of Massachusetts Amherst.
Processing a Vast Ocean of Data
While SWOT researchers are excited about the possibilities that the data is opening up, there is still much to be done. The satellite’s high-resolution view of water levels and extent means there is a vast ocean of data that researchers must wade through, and it will take some time to process and analyze the measurements.
More About SWOT
The SWOT (Surface Water and Ocean Topography) satellite is a groundbreaking collaboration led by NASA and CNES (Centre National d’Études Spatiales), with key contributions from the Canadian Space Agency (CSA) and the UK Space Agency. Managed by NASA’s Jet Propulsion Laboratory in partnership with Caltech, SWOT is designed to measure water levels and the extent of water bodies globally, providing invaluable data for hydrology, climate science, and water resource management.
NASA contributed critical flight system components, including the Ka-band radar interferometer (KaRIn), a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and the infrastructure for instrument operations. CNES provided the satellite platform, ground operations, and instruments such as the dual-frequency Poseidon altimeter, the Doppler Orbitography and Radioposition Integrated by Satellite (DORIS) system, and the KaRIn radio-frequency subsystem in collaboration with Thales Alenia Space and the UK Space Agency. The CSA played a vital role by supplying the KaRIn high-power transmitter assembly. Together, these contributions make SWOT a powerful tool for advancing our understanding of Earth’s freshwater and ocean systems.
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