UNC scientist plays key role in upcoming NASA mission to measure Earth’s water levels
When a Falcon 9 rocket takes off from California’s Vandenberg Space Force base Thursday, it will carry a satellite that represents almost two decades of UNC-Chapel Hill hydrologist Tamlin Pavelsky’s work.
The satellite will measure the height of water’s surface in lakes, rivers and oceans across the globe while also using radar to detect where water is located. Pavelsky is the United States’ hydrological science lead for the project, which is called the Surface Water and Ocean Topography mission, or SWOT.
Data from the satellite will measure the height and extent of water across the world, providing key data in remote areas or where data is not readily available, Pavelsky said at a recent talk at the Morehead Planetarium and Science Center on UNC’s campus. The satellite’s observations will likely be used to study the role oceans play in climate change, as well as information about how floodwaters move through a river system.
After reaching its orbit, the $1.1 billion satellite will unfurl, pointing the solar panels needed to keep it powered toward the sun and opening up a 33-foot boom that has radar antennas on either end.
Once operational, the satellite will send radar waves that are about a centimeter long toward the Earth, where they will bounce off the surface of water and back toward the antennas, effectively creating two triangles on either side of the satellite each covering roughly 30 miles. Using the time it takes the pulse to return to the satellite, scientists are effectively able to measure the distance the radar traveled and figure out where the surface is located.
“It’s sending down these pulses and measuring how long they take to come back and then we’re going to cover the entire globe,” Pavelsky said.
Height of the water’s surface can be combined with data about the underwater topography to figure out how much water is in lakes and reservoirs. And scientists can use changes in ocean height observed by the satellite to better understand currents.
Scientists will need to calibrate those critical instruments, but they are expected to start sending data within about 10 months.
The satellite will orbit the Earth between the 78th parallels north and south, mapping between the Arctic Ocean and the Antarctica. It will take observations of each spot on Earth roughly every 10 days, with NASA pledging to try to release data publicly within three days of receiving it.
“Would we like daily data? Assuredly,” Pavelsky said. “But we’ll take 10-day data.”
NASA expects the spacecraft to orbit for at least three and a half years, but scientists like Pavelsky are hopeful that it can stay in space for almost a decade. Landsat 5 sent data back to scientists for nearly 29 years despite an initial three-year life expectancy.
The new satellite will measure the water level, inundation extent and slope of rivers across the globe, providing key information that Pavelsky and other scientists hope to use to understand flooding. Once the data is sent back, scientists expect to be able to create a three-dimensional model of a given river that demonstrates how a flood moves through its system, ideally helping officials better predict and plan for flood events as climate change contributes to wetter storms.
“This is going to help us do a better job of modeling floods and predicting when and where there’s likely to be a flood hazard,” Pavelsky said.
There are nearly six million lakes in the world, and Pavelsky hopes to be able to measure about two million of them, capturing how big the lake is and how deep it is. Using that information, scientists can understand how the lake’s water volume is changing.
“We’re going to be able to track how the amount of water we actually have in all of the world’s reservoirs of any significant size is changing over time and that’s really, really powerful,” Pavelsky said.
Understanding oceans is also critical to the mission. Pavelsky likened oceans to a massive air conditioner for the globe, with currents taking the extra energy generated by global warming and stirring them into the ocean’s depths. With the satellite, scientists hope to glean a better grasp on how currents work and how increased warmth could be impacting the ocean.
“We really expect to have a better understanding of ocean circulation once SWOT launches,” Pavelsky said.
Snow and wetlands could present challenges for the satellite, Pavelsky said during his talk at UNC. Places where wetlands feature thick vegetation and where snow is spread across the landscape could prove difficult to measure, but those where wetlands have small grasses or where snow has melted could be mapped.
“If I had to pick two things that I fundamentally do not know about SWOT that I’ve been wondering about for a decade,” Pavelsky said, “it would be wetlands and it would be snow.”
Vice President Kamala Harris and France President Emmanual Macron discussed the upcoming mission when Macron visited NASA headquarters two weeks ago. The satellite is a joint project of NASA and the French space agency, with Canada and the United Kingdom contributing key parts.
“It’s very exciting because this innovation will actually help us to improve water management and inform — and better inform agricultural decisions. And it will also help coastal communities around the world prepare for rising seas,” Harris said.
The United States has also agreed to join the Space for Climate Observatory, a project led by the French space agency that is intended to merge satellite data with other Earth science data to help understand the impacts of a changing climate.
This story was produced with financial support from 1Earth Fund, in partnership with Journalism Funding Partners, as part of an independent journalism fellowship program. The N&O maintains full editorial control of the work.