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By NASA
Explore This Section Earth Earth Observer Editor’s Corner Feature Articles Meeting Summaries News Science in the News Calendars In Memoriam Announcements More Archives Conference Schedules Style Guide 9 min read
Harmonized Landsat and Sentinel-2: Collaboration Drives Innovation
Introduction
Landsat, a joint program of NASA and the U.S. Geological Survey (USGS), has been an invaluable tool for monitoring changes in Earth’s land surface for over 50 years. Researchers use instruments on Landsat satellites to monitor decades-long trends, including urbanization and agricultural expansion, as well as short-term dynamics, including water use and disaster recovery. However, scientists and land managers often encounter one critical limitation of this program: Landsat has a revisit time of eight days (with Landsat 8 and 9 operating), which is too long to capture events and disasters that occur on short timescales. Floods, for example, can quickly inundate a region, and cloud cover from storms can delay Landsat’s ability to get a clear observation on damage.
In 2015, the European Space Agency’s (ESA) Copernicus Sentinel-2A mission joined Landsat 7 and 8 in orbit. It was designed to collect comparable optical land data with the intention of leveraging Landsat’s archive. Two years later, ESA launched Sentinel-2B, a satellite identical to Sentinel-2A.
Led by a science team at NASA’s Goddard Space Flight Center (GSFC), the USGS, NASA, and ESA began to work on combining the capabilities of Sentinel-2 and Landsat satellites. This idea was the impetus behind Harmonized Landsat and Sentinel-2 (HLS) project, a NASA initiative that created a seamless product from the Operational Land Imager (OLI) and Multi-Spectral Instrument (MSI) aboard Landsat and Sentinel-2 satellites, respectively. HLS Version 2.0 (V2.0) is the most recent version of these data and had a global median repeat frequency of 1.6 days in 2022 by combining observations from Landsat 8 and 9 and Sentinel-2A and B. The recent addition of Sentinel-2C data will provide even more frequent observations. With near-global coverage and improved harmonization algorithms, HLS V2.0 paves the way for new applications and improved land monitoring systems – see Animation 1. HLS data are available for download on NASA Earthdata: HLSL30v2.0 and HLSS30v2.0. These data can also be accessed through Google Earth Engine: HLSL30v2.0 and HLSS30v2.0.
Animation 1. This visualization shows the change in vegetation in Maryland from January 1 to December 30, 2016, using Normalized Difference Vegetation Index (NDVI) data from Harmonized Landsat Sentinel-2 (HLS). The visualization shows land on both sides of the Chesapeake Bay, where red represents bare soil and green indicates healthy, growing vegetation. Animation credit: Michael Taylor [Science Systems and Applications Inc. (SSAI)], Matthew Radcliff [USRA], and Jeffrey Masek [GSFC]. Caption adapted from Laura Rocchio [SSAI] The Dawn of HLS
The story of HLS begins before the launch of Sentinel-2A in 2015. Jeffrey Masek [GSFC], who was at that time project scientist for Landsat 8, led a group of researchers who wanted to find a way to harmonize Landsat data with other satellite data. Their aim was to create a “virtual constellation” similar to how weather satellites operate.
“HLS meets a need that people have been asking for for a long time,” said Masek.
What began as a research question with an experimental product evolved into an operational project with the involvement of the Satellite Needs Working Group (SNWG). SNWG is an interagency effort to develop solutions that address Earth observation needs of civilian federal agencies. Every two years, SNWG conducts a survey of federal agencies to see how their work could benefit from satellite data. The answers span the gamut of application areas, from water quality monitoring to disaster recovery to planning how best to protect and use natural resources. SNWG brings these ideas to NASA, USGS, and the National Oceanic and Atmospheric Administration (NOAA) – the three main U.S. government providers of satellite data. These agencies work together to create and implement solutions that serve those needs. NASA plays a critical role in every step of the SNWG process, including leading the assessment of survey responses from over 30 federal agencies, managing and supporting the implementation of identified solutions, and encouraging solution co-design with federal partners to maximize impact.
The HLS surface reflectance product was an outcome of the very first SNWG solution cycle in 2016. This product was expanded, following additional SNWG requests in 2020 and 2022. The 2020 cycle saw the creation of nine HLS-derived vegetation indices, and the 2022 cycle aimed for a six-hour latency product.
The U.S. Department of Agriculture (USDA) now uses HLS to map crop emergence at the field scale in the corn belt, allowing farmers to better plan their growing seasons. Ranchers in Colorado use the dataset to decide where to graze their cattle during periods of drought. HLS also informs the use and termination of cover crops in the Chesapeake Bay area. In 2024, the Federal Emergency Management Agency (FEMA) employed HLS to identify where to focus aid in the aftermath of Hurricane Helene.
A New and Improved HLS
In the July 2025 issue of Remote Sensing of Environment, a team of researchers outlined the HLS V2.0 surface reflectance dataset and algorithms. The team included seven NASA co-authors, members of the 2018–2023 Landsat Science Team, and ESA. The lead author, Junchang Ju [GSFC—Remote Sensing Scientist], has been the technical lead on HLS since its inception. Co-author Christopher Neigh [GSFC—Landsat 8/9 Project Scientist] is the principal investigator on the HLS project. V2.0, which was completed in Summer 2023, incorporates several major improvements over HLS V1.4, the most recent publicly available HLS product. HLS V1.4 covered about 30% of the global land area, providing data on North America and other select locations. HLS V2.0 provides data at a spatial resolution of 30 m (98 ft) with near-global coverage from 2013 onward. The dataset includes all land masses except Antarctica. HLS V2.0 also has key algorithmic improvements in atmospheric correction, cloud masking, and bidirectional reflectance distribution function (BRDF) correction. Together, these algorithms “harmonize” the data, or ensure that the distinct Landsat and Sentinel-2 datasets can effectively be used interchangeably – see Animation 2.
Animation 2: The visualization provides the Normalized Difference Vegetation Index (NDVI) data from Harmonized Landsat Sentinel-2 (HLS) for farm fields south of Columbus, NE. The red represents bare soil and green represents healthy, growing vegetation. The animation runs from January 1 to December 30, 2016. Animation credit: Michael Taylor [SSAI], Matthew Radcliff [USRA], and Jeffrey Masek [GSFC]. Caption adapted from Laura Rocchio [SSAI] HLS V2.0 in Action
The increased frequency of observations improved the ability of the scientific community to track disaster recovery, changes in phenology, agricultural intensification, rapid urban growth, logging, and deforestation. Researchers are already putting these advances to use.
The land disturbance product (DIST-ALERT) is a global land change monitoring system that uses HLS V2.0 data to track vegetation anomalies in near real-time – see Figure 1. DIST-ALERT captures agricultural expansion, urban growth, fire, flooding, logging, drought, landslides, and other forces of change to vegetation. Amy Pickens [University of Maryland, Department of Geographical Sciences—Assistant Research Professor] said that HLS is the perfect dataset for tracking disturbances because of the frequency of observations.
DIST-ALERT was created through Observational Products for End-Users from Remote Sensing Analysis (OPERA), a project at NASA/Jet Propulsion Laboratory (JPL). OPERA products respond to agency needs identified by the SNWG. In 2018, SNWG identified tracking surface disturbance as a key need. OPERA partnered with the Global Land Analysis and Discovery (GLAD) lab at University of Maryland to develop the change detection algorithm.
To track changes in vegetation, the DIST-ALERT system establishes a rolling baseline – meaning that for any given pixel, the vegetation cover is compared against vegetation cover from the same 31-day window in the previous three years. The primary algorithm detects any vegetation loss relative to the established baseline. A secondary algorithm flags any spectral anomaly (i.e., any change in reflectance) compared to that same baseline. This approach ensures that the algorithm catches non-vegetation change (e.g., new building or road projects in unvegetated areas). Used together, these algorithms can identify long-term changes in agricultural expansion, deforestation, and urbanization alongside short-term changes in crop harvest, drought, selective logging, and the impacts of disasters. On average, DIST-ALERT is made available on LP DAAC within six hours of when new HLS data is available. Currently, the dataset does not provide attribution to disturbances.
Figure 1. In March 2025, wildfires burned through South Korea, resulting in heavy vegetation loss. [left] Output of the DIST-ALERT product on NASA Worldview from May 8, 2025, with vegetation loss in percent flagged with varying levels of confidence. Yellow and red represent areas with confirmed vegetation cover losses of right] Natural-color image captured by the Multi-Spectral Instrument (MSI) aboard Sentinel-2C on May 8, 2025. The large brown burn scar in the center of the image corresponds to vegetation loss detected by DIST-ALERT. It stands in contrast to the surrounding green vegetation. Figure credit: NASA Earthdata Disturbance alerts already exist in some ecosystems. Brazil’s National Institute for Space Research [Instituto Nacional de Pesquisas Espaciais (INPE)] runs two projects that detect deforestation in the Amazon: Programa de Cálculo do Desflorestamento da Amazônia (PRODES) and Sistema de Detecção de Desmatamento em Tempo Real (DETER). The GLAD lab created its own forest loss alerts – GLAD-L and GLAD-S2 – using Landsat and Sentinel-2 data respectively. Global Forest Watch integrates GLAD-L and GLAD-S2 data with Radar for Detecting Deforestation (RADD) observations – derived from synthetic aperture radar data from Copernicus Sentinel-1 – into an integrated deforestation alert.
The implementation of these alert systems, some of which have been around for decades, have been shown to impact deforestation rates in the tropics. For example, a 2021 study in Nature Climate Change found that deforestation alerts decreased the probability of deforestation in Central Africa by 18% relative to the average 2011–2016 levels.
DIST-ALERT is distinct from other alert systems in a few ways. First, it has global coverage. Second, the rolling baseline allows for tracking changes in seasonality and disturbances to dynamic ecosystems. When HLS V2.0 data are input to DIST-ALERT, the system is also better at identifying disturbances in cloudy ecosystems than other individual alert systems – because it is more likely to obtain clear observations. This also enables it to identify the start and end of the disturbance more precisely.
Pickens said that the DIST-ALERT team is already working with end-users who are implementing their data product. She has spoken to some who use the system to help logging companies prove that they are complying with regulations. The U.S. Census Bureau is also using DIST-ALERT to monitor fast-growing communities so that they can do targeted assessments in the interim between the larger decennial census.
Alongside DIST-ALERT, OPERA has also been developing the Dynamic Surface Water eXtent (DSWx) product suite, which employs HLS to track surface water (e.g., lakes, reservoirs, rivers, and floods) around the globe – see Figure 2. These new products represent the new applications made possible by the HLS interagency and international collaboration.
Figure 2. The map shows flood extent and estimates of flood depth in areas west of Porto Alegre, Brazil on May 6, 2024. The flood extent is from the Observational Products for End-Users from Remote Sensing Analysis (OPERA) Dynamic Surface Water eXtent product, which uses Harmonized Landsat Sentinel-2 data. The flood depth estimate is from the Floodwater Depth Estimation Tool (FwD ET). The darkest blue areas represent floodwater at least 5 m (20 ft) deep. Much of the inundated floodplain is light blue, which equates to depths of between 0.1–1 m (4–40 in). Figure credit: Lauren Dauphin [NASA’s Earth Observatory], Dinuke Munasinghe [JPL], Sagy Cohen [University of Alabama], and Alexander Handwerger [JPL] Conclusion
HLS is set to continue improving land monitoring efforts across the globe. Meanwhile, the HLS science team is working to improve the algorithms for a more seamless harmonization of Landsat 8 and 9 and Sentinel-2 data. They are also working to improve the cloud-masking algorithm, have recently released vegetation indices, and are working on developing a low-latency (six-hour) HLS surface reflectance product, all while incorporating user feedback.
Looking ahead, the launch of future Sentinel and Landsat satellites will further the development of HLS. The additional data and unique capabilities will continue to meet researchers’ need for more frequent, high-quality satellite observations of Earth’s land surface.
Madeleine Gregory
NASA’s Goddard Space Flight Center/Science Systems and Applications Inc.
madeleine.s.gregory@nasa.gov
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Last Updated Aug 25, 2025 Related Terms
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By NASA
An artist’s concept of the Starlab commercial space station.Starlab As NASA continues its transition toward a commercial low Earth orbit marketplace, an agency-supported commercial space station, Starlab, recently completed five development and design milestones. Starlab’s planned design consists of a service module and a habitat that will be launched to orbit on a single flight.
The milestones, part of a NASA Space Act Agreement awarded in 2021, focused on reviews of Starlab’s preliminary design and safety, as well as spacecraft mockup and procurement plans. Each milestone provides NASA insight into the company’s development progress.
“As we work toward the future of low Earth orbit, these milestones demonstrate Starlab’s dedication to building a commercial space station that can support human life and advance scientific research,” said Angela Hart, program manager for NASA’s Commercial Low Earth Orbit Development Program at the agency’s Johnson Space Center in Houston. “Both the insight shared by Starlab and the expertise shared by NASA are critical to future mission success.”
Starlab recently completed a preliminary design and safety review of its station’s architecture and systems. The company now will begin detailed design and hardware development, culminating in a critical design review later this year. Critical design reviews are an important step in a station’s development, assessing design maturity before proceeding with fabrication and assembly.
An artist’s concept of the Starlab commercial space station.Starlab Starlab also has begun construction of a full-scale, high-fidelity mockup of the station. The mockup, which will be housed in the Space Vehicle Mockup Facility at NASA Johnson, will be used for human-in-the-loop testing, during which participants perform day-in-the-life walkthroughs and evaluate the interior design, crew training, procedure development, hardware checks, and in-flight issue resolution.
In addition, Starlab completed reviews of the system design architecture, procurement plan, and Northrop Grumman Cygnus spacecraft docking system design. In 2023, Northrop Grumman teamed up with Starlab to provide cargo logistics services and engineering consultation to support the commercial space station. These reviews included design configuration updates of solar arrays, docking ports, crew quarters, and more.
NASA supports the design and development of multiple commercial space stations through funded and unfunded agreements. Following the design and development phase, NASA plans to procure services from one or more companies as part of its strategy to become one of many customers for low Earth orbit stations.
Learn more about commercial space stations at:
www.nasa.gov/commercialspacestations
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Earth (ESD) Earth Explore Explore Earth Home 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 1 min read
From Space to Soil: How NASA Sees Forests
NASA uses satellite lidar technology to study Earth’s forests, key carbon sinks. The GEDI mission maps forest height and biomass from the International Space Station, while ICESat-2 fills polar data gaps. Together, they enable a first-of-its-kind global biomass map, guiding smarter forest conservation and carbon tracking.
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Last Updated Jun 17, 2025 Editor Earth Science Division Editorial Team Related Terms
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By NASA
A black hole has blasted out a surprisingly powerful jet in the distant universe, according to a study from NASA’s Chandra X-ray Observatory.X-ray: NASA/CXC/CfA/J. Maithil et al.; Illustration: NASA/CXC/SAO/M. Weiss; Image Processing: NASA/CXC/SAO/N. Wolk A black hole has blasted out a surprisingly powerful jet in the distant universe, according to a new study from NASA’s Chandra X-ray Observatory and discussed in our latest press release. This jet exists early enough in the cosmos that it is being illuminated by the leftover glow from the big bang itself.
Astronomers used Chandra and the Karl G. Jansky Very Large Array (VLA) to study this black hole and its jet at a period they call “cosmic noon,” which occurred about three billion years after the universe began. During this time most galaxies and supermassive black holes were growing faster than at any other time during the history of the universe.
The main graphic is an artist’s illustration showing material in a disk that is falling towards a supermassive black hole. A jet is blasting away from the black hole towards the upper right, as Chandra detected in the new study. The black hole is located 11.6 billion light-years from Earth when the cosmic microwave background (CMB), the leftover glow from the big bang, was much denser than it is now. As the electrons in the jets fly away from the black hole, they move through the sea of CMB radiation and collide with microwave photons. These collisions boost the energy of the photons up into the X-ray band (purple and white), allowing them to be detected by Chandra even at this great distance, which is shown in the inset.
Researchers, in fact, identified and then confirmed the existence of two different black holes with jets over 300,000 light-years long. The two black holes are 11.6 billion and 11.7 billion light-years away from Earth, respectively. Particles in one jet are moving at between 95% and 99% of the speed of light (called J1405+0415) and in the other at between 92% and 98% of the speed of light (J1610+1811). The jet from J1610+1811 is remarkably powerful, carrying roughly half as much energy as the intense light from hot gas orbiting the black hole.
The team was able to detect these jets despite their great distances and small separation from the bright, growing supermassive black holes — known as “quasars” — because of Chandra’s sharp X-ray vision, and because the CMB was much denser then than it is now, enhancing the energy boost described above.
When quasar jets approach the speed of light, Einstein’s theory of special relativity creates a dramatic brightening effect. Jets aimed toward Earth appear much brighter than those pointed away. The same brightness astronomers observe can come from vastly different combinations of speed and viewing angle. A jet racing at near-light speed but angled away from us can appear just as bright as a slower jet pointed directly at Earth.
The researchers developed a novel statistical method that finally cracked this challenge of separating effects of speed and of viewing angle. Their approach recognizes a fundamental bias: astronomers are more likely to discover jets pointed toward Earth simply because relativistic effects make them appear brightest. They incorporated this bias using a modified probability distribution, which accounts for how jets oriented at different angles are detected in surveys.
Their method works by first using the physics of how jet particles scatter the CMB to determine the relationship between jet speed and viewing angle. Then, instead of assuming all angles are equally likely, they apply the relativistic selection effect: jets beamed toward us (smaller angles) are overrepresented in our catalogs. By running ten thousand simulations that match this biased distribution to their physical model, they could finally determine the most probable viewing angles: about 9 degrees for J1405+0415 and 11 degrees for J1610+1811.
These results were presented by Jaya Maithil (Center for Astrophysics | Harvard & Smithsonian) at the 246th meeting of the American Astronomical Society in Anchorage, AK, and are also being published in The Astrophysical Journal. A preprint is available here. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
Read more from NASA’s Chandra X-ray Observatory Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
Visual Description
This release is supported by an artist’s illustration of a jet blasting away from a supermassive black hole.
The black hole sits near the center of the illustration. It resembles a black marble with a fine yellow outline. Surrounding the black hole is a swirling disk, resembling a dinner plate tilted to face our upper right. This disk comprises concentric rings of fiery swirls, dark orange near the outer edge, and bright yellow near the core.
Shooting out of the black hole are two streaky beams of silver and pale violet. One bright beam shoots up toward our upper right, and a second somewhat dimmer beam shoots in the opposite direction, down toward our lower left. These beams are encircled by long, fine, corkscrewing lines that resemble stretched springs.
This black hole is located 11.6 billion light-years from Earth, much earlier in the history of the universe. Near this black hole, the leftover glow from the big bang, known as the cosmic microwave background or CMB, is much denser than it is now. As the electrons in the jets blast away from the black hole, they move through the sea of CMB radiation. The electrons boost the energies of the CMB light into the X-ray band, allowing the jets to be detected by Chandra, even at this great distance.
Inset at our upper righthand corner is an X-ray image depicting this interaction. Here, a bright white circle is ringed with a band of glowing purple energy. The jet is the faint purple line shooting off that ring, aimed toward our upper right, with a blob of purple energy at its tip.
News Media Contact
Megan Watzke
Chandra X-ray Center
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617-496-7998
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Lane Figueroa
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
lane.e.figueroa@nasa.gov
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By NASA
NASA’s James Webb Space Telescope recently imaged the Sombrero Galaxy with its NIRCam (Near-Infrared Camera), which shows dust from the galaxy’s outer ring blocking stellar light from stars within the galaxy. In the central region of the galaxy, the roughly 2,000 globular clusters, or collections of hundreds of thousands of old stars held together by gravity, glow in the near-infrared. The Sombrero Galaxy is around 30 million light-years from Earth in the constellation Virgo. From Earth, we see this galaxy nearly “edge-on,” or from the side.NASA, ESA, CSA, STScI After capturing an image of the iconic Sombrero galaxy at mid-infrared wavelengths in late 2024, NASA’s James Webb Space Telescope has now followed up with an observation in the near-infrared. In the newest image, released on June 3, 2025, the Sombrero galaxy’s tightly packed group of stars at the galaxy’s center is illuminated while the dust in the outer edges of the disk blocks some stellar light. Studying galaxies like the Sombrero at different wavelengths, including the near-infrared and mid-infrared with Webb, as well as the visible with NASA’s Hubble Space Telescope, helps astronomers understand how this complex system of stars, dust, and gas formed and evolved, along with the interplay of that material.
Learn more about the Sombrero galaxy and what this new view can tell us.
Image credit: NASA, ESA, CSA, STScI
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