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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
A ship plows through rough seas in the Bering Sea in the aftermath of Typhoon Tip, one of the largest hurricanes on record. The Sentinel-6B satellite will provide data crucial to forecasting sea states, information that can help ships avoid danger. CC BY 2.0 NOAA/Commander Richard Behn Sea surface height data from the Sentinel-6B satellite, led by NASA and ESA, will help with the development of marine weather forecasts, alerting ships to possible dangers.
Because most global trade travels by ship, accurate, timely ocean forecasts are essential. These forecasts provide crucial information about storms, high winds, and rough water, and they depend on measurements provided by instruments in the ocean and by satellites including Sentinel-6B, a joint mission led by NASA and ESA (European Space Agency) that will provide essential sea level and other ocean data after it launches this November.
The satellite will eventually take over from its twin, Sentinel-6 Michael Freilich, which launched in 2020. Both satellites have an altimeter instrument that measures sea levels, wind speeds, and wave heights, among other characteristics, which meteorologists feed into models that produce marine weather forecasts. Those forecasts provide information on the state of the ocean as well as the changing locations of large currents like the Gulf Stream. Dangerous conditions can result when waves interact with such currents, putting ships at risk.
“Building on NASA’s long legacy of satellite altimetry data and its real-world impact on shipping operations, Sentinel-6B will soon take on the vital task of improving ocean and weather forecasts to help keep ships, their crews, and cargo safe”, said Nadya Vinogradova Shiffer, lead program scientist at NASA Headquarters in Washington.
Sentinel-6 Michael Freilich and Sentinel-6B are part of the Sentinel-6/Jason-CS (Continuity of Service) mission, the latest in a series of ocean-observing radar altimetry missions that have monitored Earth’s changing seas since the early 1990s. Sentinel-6/Jason-CS is a collaboration between NASA, ESA, the European Union, EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites), and NOAA (U.S. National Oceanic and Atmospheric Administration). The European Commission provided funding support, and the French space agency CNES (Centre National d’Études Spatiales) contributed technical support.
Keeping current
“The ocean is getting busier, but it’s also getting more dangerous,” said Avichal Mehra, deputy director of the Ocean Prediction Center at the National Weather Service in College Park, Maryland. He and his colleagues produce marine weather forecasts using data from ocean-based instruments as well as complementary measurements from five satellites, including Sentinel-6 Michael Freilich. Among those measurements: sea level, wave height, and wind speed. The forecasters derive the location of large currents from changes in sea level.
One of the planet’s major currents, the Gulf Stream is located off the southeastern coast of the United States, but its exact position varies. “Ships will actually change course depending on where the Gulf Stream is and the direction of the waves,” said Mehra. “There have been instances where, in calm conditions, waves interacting with the Gulf Stream have caused damage or the loss of cargo containers on ships.”
Large, warm currents like the Gulf Stream can have relatively sharp boundaries since they are generally higher than their surroundings. Water expands as it warms, so warm seawater is taller than cooler water. If waves interact with these currents in a certain way, seas can become extremely rough, presenting a hazard to even the largest ships.
“Satellite altimeters are the only reliable measurement we have of where these big currents can be,” said Deirdre Byrne, sea surface height team lead at NOAA in College Park.
There are hundreds of floating sensors scattered about the ocean that could pick up parts of where such currents are located, but these instruments are widely dispersed and limited in the area they measure at any one time. Satellites like Sentinel-6B offer greater spatial coverage, measuring areas that aren’t regularly monitored and providing essential information for the forecasts that ships need.
Consistency is key
Sentinel-6B won’t just help marine weather forecasts through its near-real-time data, though. It will also extend a long-term dataset featuring more than 30 years of sea level measurements, just as Sentinel-6 Michael Freilich does today.
“Since 1992, we have launched a series of satellites that have provided consistent sea level observations from the same orbit in space. This continuity allows each new mission to be calibrated against its predecessors, providing measurements with centimeter-level accuracy that don’t drift over time,” said Severine Fournier, Sentinel-6B deputy project scientist at NASA’s Jet Propulsion Laboratory in Southern California.
This long-running, repeated measurement has turned this dataset into the gold standard sea level measurement from space — a reference against which data from other sea level satellites is checked. It also serves as a baseline, giving forecasters a way to tell what ocean conditions have looked like over time and how they are changing now. “This kind of data can’t be easily replaced,” said Mehra.
More about Sentinel-6B
Sentinel-6/Jason-CS was jointly developed by ESA, EUMETSAT, NASA, and NOAA, with funding support from the European Commission and technical support from CNES.
A division of Caltech in Pasadena, JPL contributed three science instruments for each Sentinel-6 satellite: the Advanced Microwave Radiometer, the Global Navigation Satellite System – Radio Occultation, and the Laser Retroreflector Array. NASA is also contributing launch services, ground systems supporting operation of the NASA science instruments, the science data processors for two of these instruments, and support for the U.S. members of the international Ocean Surface Topography and Sentinel-6 science teams.
For more about Sentinel-6/Jason-CS, visit:
https://sealevel.jpl.nasa.gov/missions/jason-cs-sentinel-6
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Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
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Last Updated Sep 11, 2025 Related Terms
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Earth (ESD) Earth Explore Explore Earth Home Agriculture Air Quality Climate Change Freshwater Life on Earth Severe Storms Snow and Ice The Global Ocean Science at Work Earth Science at Work Technology and Innovation Powering Business Multimedia Image Collections Videos Data For Researchers About Us 5 Min Read NASA Data, Trainings Help Uruguay Navigate Drought
Uruguay’s Paso Severino Reservoir, the primary water source for Montevideo, on June 13, 2023, captured by Landsat 9. Credits:
NASA Earth Observatory/ Wanmei Liang Lee esta historia en español aquí.
NASA satellite data and trainings helped Uruguay create a drought-response tool that its National Water Authority now uses to monitor reservoirs and guide emergency decisions. A similar approach could be applied in the United States and other countries around the world.
From 2018 to 2023, Uruguay experienced its worst drought in nearly a century. The capital city of Montevideo, home to nearly 2 million people, was especially hard hit. By mid-2023, Paso Severino, the largest reservoir and primary water source for Montevideo, had dropped to just 1.7% of its capacity. As water levels declined, government leaders declared an emergency. They began identifying backup supplies and asked: Was there water left in other upstream reservoirs — mainly used for livestock and irrigation — that could help?
That’s when environmental engineer Tiago Pohren and his colleagues at the National Water Authority (DINAGUA – Ministry of Environment) turned to NASA data and trainings to build an online tool that could help answer that question and improve monitoring of the nation’s reservoirs.
“Satellite data can inform everything from irrigation scheduling in the Great Plains to water quality management in the Chesapeake Bay,” said Erin Urquhart, manager of the water resources program at NASA Headquarters in Washington. “NASA provides the reliable data needed to respond to water crises anywhere in the world.”
Learning to Detect Water from Space
The DINAGUA team learned about NASA resources during a 2022 workshop in Buenos Aires, organized by the Interagency Science and Applications Team (ISAT). Led by NASA, the U.S. Army Corps of Engineers, and the U.S. Department of State, the workshop focused on developing tools to help manage water in the La Plata River Basin, which spans multiple South American countries including Uruguay.
At the workshop, researchers from NASA introduced participants to methods for measuring water resources from space. NASA’s Applied Remote Sensing (ARSET) program also provided a primer on remote sensing principles.
DINAGUA team supervisor Jose Rodolfo Valles León asks a question during a 2022 workshop in Buenos Aires. Other members of the Uruguay delegation — Florencia Hastings, Vanessa Erasun Rodríguez de Líma, Vanessa Ferreira, and Teresa Sastre (current Director of DINAGUA) — sit in the row behind. Organization of American States “NASA doesn’t just deliver data,” said John Bolten, NASA’s lead scientist for ISAT and chief of the Hydrological Sciences Laboratory at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We collaborate with our partners and local experts to translate the data into information that is useful, usable, and relevant. That kind of coordination is what makes NASA’s water programs so effective on the ground, at home and around the world.”
The DINAGUA team brought ideas and provided guidelines to Pohren for a tool that applies Landsat and Sentinel satellite imagery to detect changes in Uruguay’s reservoirs. Landsat, a joint NASA-U.S. Geological Survey mission, provides decades of satellite imagery to track changes in land and water. The Sentinel missions, a part of the European Commission managed Copernicus Earth Observation program and operated by ESA (the European Space Agency), provide complementary visible, infrared, and microwave imagery for surface water assessments.
From a young age, Pohren was familiar with water-related challenges, as floods repeatedly inundated his relatives’ homes in his hometown of Montenegro, Brazil. It was extra motivation for him as he scoured ARSET tutorials and taught himself to write computer code. The result was a monitoring tool capable of estimating the surface area of Uruguay’s reservoirs over time.
A screenshot of the reservoir monitoring tool shows the Paso Severino’s surface water coverage alongside time-series data tracking its variations. Tiago Pohren The tool draws on several techniques to differentiate the surface water extent of reservoirs. These techniques include three optical indicators derived from the Landsat 8 and Sentinel-2 satellites:
Normalized Difference Water Index, which highlights water by comparing how much green and near-infrared light is reflected. Water absorbs infrared light, so it stands out clearly from land. Modified Normalized Difference Water Index, which swaps near-infrared with shortwave infrared to improve the contrast and reduce errors when differentiating between water and built-up or vegetated areas. Automated Water Extraction Index, which combines four types of reflected light — green, near-infrared, and two shortwave infrared bands — to help separate water from shadows and other dark features. From Emergency Tool to Everyday Asset
In 2023, the DINAGUA team used Pohren’s tool to examine reservoirs located upstream from Montevideo’s drinking water intake. But the data told a tough story.
“There was water available in other reservoirs, but it was a very small amount compared to the water demand of the Montevideo metropolitan region,” Pohren said. Simulations showed that even if all of the water were released, most of it would not reach the water intake for Montevideo or the Paso Severino reservoir.
Despite this news, the analysis prevented actions that might have wasted important resources for maintaining productive activities in the upper basin, Pohren said. Then, in August 2023, rain began to refill Uruguay’s reservoirs, allowing the country to declare an end to the water crisis.
From right to left: Tiago Pohren, Vanessa Erasun, and Florencia Hastings at the second ISAT workshop in March 2024. Organization of American States Though the immediate water crisis has passed, the tool Pohren created will be useful in the future in Uruguay and around the world. During an ISAT workshop in 2024, he shared his tool with international water resources managers with the hope it could aid their own drought response efforts. And DINAGUA officials still use it to identify and monitor dams, irrigation reservoirs, and other water bodies in Uruguay.
Pohren continues to use NASA training and data to advance reservoir management. He’s currently exploring an ARSET training on how the Surface Water and Ocean Topography (SWOT) mission will further improve the system by allowing DINAGUA to directly measure the height of water in reservoirs. He is also following NASA’s new joint mission with ISRO (the Indian Space Research Organization) called NISAR, which launched on July 30. The NISAR satellite will provide radar data that detects changes in water extent, regardless of cloud cover or time of day. “If a drought happens again,” Pohren said, “with the tools that we have now, we will be much more prepared to understand what the conditions of the basin are and then make predictions.”
Environmental engineer Tiago Pohren conducts a field inspection on the Canelón Grande reservoir, the second-largest reservoir serving Montevideo, during the drought. Tiago Pohren By Melody Pederson, Rachel Jiang
The authors would like to thank Noelia Gonzalez, Perry Oddo, Denise Hill, and Delfina Iervolino for interview support as well as Jerry Weigel for connecting with Tiago about the tool’s development.
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Last Updated Sep 10, 2025 Related Terms
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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
These maps of Prince George’s County, MD, show surface temperatures collected a few hours apart on July 30, 2023 from the Landsat 9 satellite and the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) instrument. The dark blue spots in the right hand image are likely clouds that formed in the afternoon.Credit: Stephanie Schollaert Uz, NASA Goddard Space Flight Center Thousands of Americans are impacted each summer by excessive heat and humidity, some suffering from heat-related illnesses when the body can’t cool itself down. Data from NASA satellites could help local governments reduce the sweltering risks, thanks to a collaboration between NASA scientists and officials in Prince George’s County, Maryland. The effort demonstrates how local officials in other communities could turn to NASA data to inform decisions that provide residents with relief from summer heat.
NASA researchers and their Prince George’s County collaborators reported in Frontiers in Environmental Science that they used the Landsat 8 satellite, jointly operated by NASA and the US Geological Survey, and NASA’s Aqua satellite, to gain insight into surface temperature trends across the county over the past few decades. The data also show how temperatures have responded to changing land use and construction. It is information that county planners and environmental experts hope can aid them in their attempts to remediate and prevent heat dangers in the future. The collaboration may also help the county’s first responders anticipate and prepare for heat-related emergencies and injuries.
Cooperation with Prince George’s County expands on NASA’s historic role, said Stephanie Schollaert Uz, an applications scientist with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and one of the study authors. “Applying government satellite data to county-level problems is new here. We’re trying to make it easier for people outside of NASA to use our data, in part by including how-to guides referenced at the end of our paper,” Schollaert Uz said.
In the long run, county officials hope to use NASA satellites to track the negative health impacts that arise from land use and modification. Removal of tree cover and the construction of non-permeable roads, parking lots, and structures that lead to water runoff are among the factors that create heat islands, where temperatures in localized areas soar relative to the surrounding landscape. In addition to the direct dangers of heat for county residents and workers, areas with higher-than-normal temperatures can drive intense local weather events.
“There’s potentially a greater incidence of microbursts,” said Mary Abe of Prince George’s County’s sustainability division. “The atmosphere can become supercharged over hot spots,” causing high winds and flood-inducing rains.
Prince George’s County planners anticipate relying on NASA satellites to determine where residents and county employees are at greater risk, predict how future construction could impact heat dangers, and develop strategies to moderate heat in areas currently experiencing elevated summer temperatures. Efforts might include protecting existing trees and planting new ones. It could include replacing impermeable surfaces (cement, pavement, etc.) with alternatives that let water soak into the ground rather than running off into storm drains. To verify and calibrate the satellite observations crucial for such planning, county experts are considering enlisting residents to act as citizen scientists to collect temperature and weather data on the ground, Abe said.
Eventually, the NASA satellite temperature data could also lead to strategies to curb insect-borne diseases, said Evelyn Hoban, associate director for the Prince George’s County division of environmental health and communicable disease. “Once we know where the higher temperatures are, we can check to see if they create mosquito or tick breeding grounds,” said Hoban, who coauthored the study. “We could then focus our outreach and education, and perhaps prevention efforts, on areas of greater heat and risk.”
A NASA guide is available to aid other communities who hope to duplicate the Prince George’s County study. The guide provides introductions on a variety of NASA satellite and ground-based weather station data. Instructions for downloading and analyzing the data are illustrated in an accompanying tutorial that uses the Prince George’s County study as an example for other communities to follow on their own.
One of the greatest benefits of the collaboration, Abe said, is the boost in credibility that comes from incorporating NASA resources and expertise in the county’s efforts to improve safety and health. “It’s partly the NASA brand. People recognize it and they’re really intrigued by it,” she said. “Working with NASA builds confidence that the decision-making process is based firmly in science.”
By James Riordon
NASA Goddard Space Flight Center
Media contact: Elizabeth Vlock
NASA Headquarters
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By NASA
5 min read
Astronomers Map Stellar ‘Polka Dots’ Using NASA’s TESS, Kepler
Scientists have devised a new method for mapping the spottiness of distant stars by using observations from NASA missions of orbiting planets crossing their stars’ faces. The model builds on a technique researchers have used for decades to study star spots.
By improving astronomers’ understanding of spotty stars, the new model — called StarryStarryProcess — can help discover more about planetary atmospheres and potential habitability using data from telescopes like NASA’s upcoming Pandora mission.
“Many of the models researchers use to analyze data from exoplanets, or worlds beyond our solar system, assume that stars are uniformly bright disks,” said Sabina Sagynbayeva, a graduate student at Stony Brook University in New York. “But we know just by looking at our own Sun that stars are more complicated than that. Modeling complexity can be difficult, but our approach gives astronomers an idea of how many spots a star might have, where they are located, and how bright or dark they are.”
A paper describing StarryStarryProcess, led by Sagynbayeva, published Monday, August 25, in The Astrophysical Journal.
Watch to learn how a new tool uses data from exoplanets, worlds beyond our solar system, to tell us about their polka-dotted stars.
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NASA’s TESS (Transiting Exoplanet Survey Satellite) and now-retired Kepler Space Telescope were designed to identify planets using transits, dips in stellar brightness caused when a planet passes in front of its star.
These measurements reveal how the star’s light varies with time during each transit, and astronomers can arrange them in a plot astronomers call a light curve. Typically, a transit light curve traces a smooth sweep down as the planet starts passing in front of the star’s face. It reaches a minimum brightness when the world is fully in front of the star and then rises smoothly as the planet exits and the transit ends.
By measuring the time between transits, scientists can determine how far the planet lies from its star and estimate its surface temperature. The amount of missing light from the star during a transit can reveal the planet’s size, which can hint at its composition.
Every now and then, though, a planet’s light curve appears more complicated, with smaller dips and peaks added to the main arc. Scientists think these represent dark surface features akin to sunspots seen on our own Sun — star spots.
The Sun’s total number of sunspots varies as it goes through its 11-year solar cycle. Scientists use them to determine and predict the progress of that cycle as well as outbreaks of solar activity that could affect us here on Earth.
Similarly, star spots are cool, dark, temporary patches on a stellar surface whose sizes and numbers change over time. Their variability impacts what astronomers can learn about transiting planets.
Scientists have previously analyzed transit light curves from exoplanets and their host stars to look at the smaller dips and peaks. This helps determine the host star’s properties, such as its overall level of spottiness, inclination angle of the planet’s orbit, the tilt of the star’s spin compared to our line of sight, and other factors. Sagynbayeva’s model uses light curves that include not only transit information, but also the rotation of the star itself to provide even more detailed information about these stellar properties.
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This artist’s concept illustrates the varying brightness of star with a transiting planet and several star spots. NASA’s Goddard Space Flight Center “Knowing more about the star in turn helps us learn even more about the planet, like a feedback loop,” said co-author Brett Morris, a senior software engineer at the Space Telescope Science Institute in Baltimore. “For example, at cool enough temperatures, stars can have water vapor in their atmospheres. If we want to look for water in the atmospheres of planets around those stars — a key indicator of habitability — we better be very sure that we’re not confusing the two.”
To test their model, Sagynbayeva and her team looked at transits from a planet called TOI 3884 b, located around 141 light-years away in the northern constellation Virgo.
Discovered by TESS in 2022, astronomers think the planet is a gas giant about five times bigger than Earth and 32 times its mass.
The StarryStarryProcess analysis suggests that the planet’s cool, dim star — called TOI 3384 — has concentrations of spots at its north pole, which also tips toward Earth so that the planet passes over the pole from our perspective.
Currently, the only available data sets that can be fit by Sagynbayeva’s model are in visible light, which excludes infrared observations taken by NASA’s James Webb Space Telescope. But NASA’s upcoming Pandora mission will benefit from tools like this one. Pandora, a small satellite developed through NASA’s Astrophysics Pioneers Program, will study the atmospheres of exoplanets and the activity of their host stars with long-duration multiwavelength observations. The Pandora mission’s goal is to determine how the properties of a star’s light differs when it passes through a planet’s atmosphere so scientists can better measure those atmospheres using Webb and other missions.
“The TESS satellite has discovered thousands of planets since it launched in 2018,” said Allison Youngblood, TESS project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “While Pandora will study about 20 worlds, it will advance our ability to pick out which signals come from stars and which come from planets. The more we understand the individual parts of a planetary system, the better we understand the whole — and our own.”
Facebook logo @NASAUniverse @NASAUniverse Instagram logo @NASAUniverse By Jeanette Kazmierczak
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Media Contact:
Alise Fisher
202-358-2546
alise.m.fisher@nasa.gov
NASA Headquarters, Washington
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Last Updated Aug 25, 2025 Related Terms
Astrophysics Exoplanet Atmosphere Exoplanets Galaxies, Stars, & Black Holes Galaxies, Stars, & Black Holes Research Goddard Space Flight Center Kepler / K2 Stars TESS (Transiting Exoplanet Survey Satellite) The Universe View the full article
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