Once in orbit, the SWOT mission will regularly monitor not only mighty rivers like Oregon’s Willamette, pictured, but also smaller waterways that are at least 330 feet (100 meters) across. Credits: U.S. Department of Energy
How
and why SWOT will study small ocean currents
Read a Q&A with SWOT’s project manager
The Surface Water and Ocean Topography mission will make
measurements of over 95% of Earth’s lakes, rivers, and reservoirs.
Water is life, but for all its importance, humanity has a
surprisingly limited view of Earth’s freshwater bodies. Researchers have
reliable water level measurements for only a few thousand lakes around the
world, and little to no data on some of the planet’s important river systems.
The upcoming Surface Water and Ocean Topography (SWOT) satellite will fill that enormous gap. By helping to
provide a better understanding of Earth’s water cycle, it will both aid in
better management of water resources and expand knowledge of how climate change
affects lakes, rivers, and reservoirs.
A collaboration
between NASA and the French space agency Centre National d’Études Spatial
(CNES), with contributions from the Canadian Space Agency and the United
Kingdom Space Agency, SWOT is scheduled to launch in November from Vandenberg
Space Force Base in California. Engineers and technicians are finishing up work
on the satellite in a facility run by Thales Alenia Space in Cannes, France.
SWOT has several key tasks, including
measuring the height of water bodies on Earth’s surface. Over the ocean, the
satellite will be able to “see” features like eddies less than 60 miles (100 kilometers)
across – smaller than those that previous sea level satellites could observe.
SWOT will also measure more than 95% of Earth’s lakes larger than 15 acres (6
hectares) and rivers wider than 330 feet (100 meters) across.
“Current databases maybe have information
on a couple thousand lakes around the world,” said Tamlin Pavelsky, the NASA
freshwater science lead for SWOT, based at the University of North Carolina,
Chapel Hill. “SWOT will push that number to between 2 million and 6 million.”
Along with measuring the water height –
whether it be in a lake, river, or reservoir – SWOT will also measure its
extent, or surface area. That crucial information will enable scientists to
calculate how much water moves through freshwater bodies. “Once you get hold of
the volume of water, you can better assess the water budget, or how much water
flows into and out of an area,” said Lee-Lueng Fu, SWOT project scientist at
NASA’s Jet Propulsion Laboratory in Southern California, which manages the U.S.
portion of the mission.
This is important because climate change
is accelerating Earth’s water cycle. Warmer temperatures mean the atmosphere
can hold more water (in the form of water vapor), which can cause, for example,
rain storms to be stronger than a region might typically see. This, in turn,
can wreak havoc on farms, damaging crops. Such accelerating changes can make
managing a community’s water resources more difficult.
“As Earth’s water cycle intensifies,
predicting future extreme events like floods and droughts requires monitoring
both changes in water supply from the ocean and water demand and usage on land.
SWOT’s global look at all surface water on Earth will give us exactly that,”
said Nadya Vinogradova Shiffer, SWOT’s program scientist at NASA Headquarters
in Washington.
A
Bigger, Better Picture
SWOT will provide its game-changing data
using a new instrument called the Ka-band Radar Interferometer (KaRIn), which
bounces radar pulses off the water’s surface and receives the return signal
with two antennas at the same time. The antennas are spaced 33 feet (10 meters)
apart on a boom, enabling researchers to gather information along a roughly
75-mile-wide (120-kilometer-wide) swath of Earth’s surface – a wider path than
that of the satellite’s predecessors.
The engineering required for this kind of
system is tricky because such a large antenna boom requires incredible
stability, and because researchers need very precise calculations to produce
measurements of Earth’s ocean and freshwater bodies. “The basic idea of SWOT
dates back to the late 1990s, but turning that concept into reality – all that
engineering – took a huge amount of time and effort,” Pavelsky said.
Satellites already in orbit can measure
water height – in the ocean, very large lakes, and very wide rivers – or the
surface area of a water body. But to calculate changes in volume over time,
scientists need to match up the extent and height measurements that different
instruments took on different days. This makes it difficult to determine basic
details, like how much water flows through the world’s rivers and how much that
volume varies. “You’d think we would already know this,” said Pavelsky. “But
for a lot of rivers in the world, there just aren’t a lot of these kinds of
measurements.”
SWOT will eliminate the need to cobble
together the extent and height information from different satellites, and at
the same time the satellite will give researchers a global view of Earth’s
surface water. “It will be a tremendous change in our knowledge and
understanding of fresh water,” said Sylvain Biancamaria, a SWOT science team
member and freshwater researcher at the Laboratoire d’Études en Géophysique et
Océanographie Spatiales in Toulouse, France.
Some studies, including one published last year in Nature, have used water level
measurements to look at how lakes and rivers around the world change over time.
However, the data that researchers expect from SWOT will provide a
better understanding of water levels and surface area, both of which will be
sampled more frequently and over a greater area of Earth. Once in orbit, SWOT
will be sending back about one terabyte of unprocessed data a day.
Scientists like Biancamaria and Pavelsky
are especially looking forward to getting information at the basin level, or
the area of land drained by a lake or a river and its tributaries. “From a
societal point of view – whether you’re looking at drinking water, navigation,
flood control – water needs to be managed at basin scale,” said Biancamaria.
“Therefore, observations covering the entire basin are needed, and SWOT will
provide such data sets.”
More
About the Mission
SWOT is being jointly developed by NASA
and CNES, with contributions from the Canadian Space Agency and the United
Kingdom Space Agency. JPL, which is managed for NASA by Caltech in Pasadena,
California, leads the U.S. component of the project. For the flight system
payload, NASA is providing the KaRIn instrument, a GPS science receiver, a
laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations.
CNES is providing the Doppler Orbitography and Radioposition Integrated by
Satellite (DORIS) 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 platform, and
ground control segment. CSA is providing the KaRIn high-power transmitter
assembly. NASA is providing the launch vehicle and associated launch services.
To learn more about SWOT, visit: https://swot.jpl.nasa.gov/
Source: US-European
Satellite Will Make World’s First Global Freshwater Survey | NASA
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