Data from the SWOT satellite was used to calculate
average water levels for lakes and reservoirs in the Ohio River Basin from July
2023 to November 2024. Yellow indicates values greater than 1,600 feet (500
meters) above sea level; dark purple represents water levels less than 330 feet
(100 meters).
Data from the U.S.-European Surface Water and Ocean Topography mission
gives researchers a detailed look at lakes and reservoirs in a U.S. watershed.
The Ohio River Basin stretches from
Pennsylvania to Illinois and contains a system of reservoirs, lakes, and rivers
that drains an area almost as large as France. Researchers with the SWOT
(Surface Water and Ocean Topography) mission, a collaboration between NASA and
the French space agency CNES (Centre National d’Études Spatiales), now have a
new tool for measuring water levels not only in this area, which is home to
more than 25 million people, but in other watersheds around the world as well.
Since early 2023, SWOT has been measuring the height of nearly all
water on Earth’s surface — including oceans, lakes, reservoirs, and rivers —
covering nearly the entire globe at least once every 21 days. The SWOT
satellite also measures the horizontal extent of water in freshwater bodies.
Earlier this year, the mission started making validated data publicly
available.
“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.
The visualization above 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.
Complementing
a Patchwork of Data
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.
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.
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 satellite was
jointly developed by NASA and CNES, with contributions from the Canadian Space
Agency (CSA) and the UK Space Agency. NASA’s Jet Propulsion Laboratory, managed
for the agency by Caltech in Pasadena, California, leads the U.S. component of
the project. For the flight system payload, NASA provided the Ka-band radar
interferometer (KaRIn) instrument, a GPS science receiver, a laser
retroreflector, a two-beam microwave radiometer, and NASA instrument
operations. The Doppler Orbitography and Radioposition Integrated by
Satellite system, the dual frequency Poseidon altimeter (developed by Thales
Alenia Space), the KaRIn radio-frequency subsystem (together with Thales Alenia
Space and with support from the UK Space Agency), the satellite platform, and
ground operations were provided by CNES. The KaRIn high-power transmitter
assembly was provided by CSA.
To learn more about SWOT, visit:
By: Jet Propulsion Laboratory
Source: Cutting-Edge Satellite Tracks Lake Water Levels in Ohio River Basin - NASA
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