Members Can Post Anonymously On This Site
-
Similar Topics
-
By European Space Agency
The Japan Aerospace Exploration Agency (JAXA) has requested funding to participate in the European Space Agency’s (ESA) Rapid Apophis Mission for Space Safety (Ramses).
View the full article
-
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
Share
Details
Last Updated Aug 25, 2025 Related Terms
Earth Science View the full article
-
By NASA
Technicians have successfully installed two sunshields onto NASA’s Nancy Grace Roman Space Telescope’s inner segment. Along with the observatory’s Solar Array Sun Shield and Deployable Aperture Cover, the panels (together called the Lower Instrument Sun Shade), will play a critical role in keeping Roman’s instruments cool and stable as the mission explores the infrared universe.
To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video
This video shows technicians installing two sunshields onto NASA's nearly complete Nancy Grace Roman Space Telescope on July 17. The large yet lightweight panels will block sunlight, keeping Roman’s instruments cool and stable as the mission explores the infrared universe.Credit: NASA/Sophia Roberts The team is on track to join Roman’s outer and inner assemblies this fall to complete the full observatory, which can then undergo further prelaunch testing.
“This shield is like an extremely strong sunblock for Roman’s sensitive instruments, protecting them from heat and light from the Sun that would otherwise overwhelm our ability to detect faint signals from space,” said Matthew Stephens, an aerospace engineer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The sunshade, which was designed and engineered at NASA Goddard, is essentially an extension of Roman’s solar panels, except without solar cells. Each sunshade flap is roughly the size of a garage door — about 7 by 7 feet (2.1 by 2.1 meters) — and 3 inches (7.6 centimeters) thick.
“They’re basically giant aluminum sandwiches, with metal sheets as thin as a credit card on the top and bottom and the central portion made up of a honeycomb structure,” said Conrad Mason, an aerospace engineer at NASA Goddard.
This design makes the panels lightweight yet stiff, and the material helps limit heat transfer from the side facing the Sun to the back—no small feat considering the front will be hot enough to boil water (up to 216 degrees Fahrenheit, or 102 degrees Celsius) while the back will be much colder than Antarctica’s harshest winter (minus 211 Fahrenheit, or minus 135 Celsius). A specialized polymer film blanket will wrap around each panel to temper the heat, with 17 layers on the Sun side and one on the shaded side.
The sunshade will be stowed and gently deploy around an hour after launch.
To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video
In this time-lapse video, technicians manually deploy the Lower Instrument Sun Shield for NASA's Nancy Grace Roman Space Telescope. The test helps verify the panels will operate as designed in space.NASA/Sophia Roberts “The deploying mechanisms have dampers that work like soft-close hinges for drawers or cabinets, so the panels won’t slam open and rattle the observatory,” Stephens said. “They each take about two minutes to move into their final positions. This is the very first system that Roman will deploy in space after the spacecraft separates from the launch vehicle.”
Now completely assembled, Roman’s inner segment is slated to undergo a 70-day thermal vacuum test next. Engineers and scientists will test the full functionality of the spacecraft, telescope, and instruments under simulated space conditions. Following the test, the sunshade will be temporarily removed while the team joins Roman’s outer and inner assemblies, and then reattached to complete the observatory. The mission remains on track for launch no later than May 2027 with the team aiming for as early as fall 2026.
Click here to virtually tour an interactive version of the telescope Download high-resolution video and images from NASA’s Scientific Visualization Studio
The Nancy Grace Roman Space Telescope is managed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation by NASA’s Jet Propulsion Laboratory in Southern California; Caltech/IPAC in Pasadena, California; the Space Telescope Science Institute in Baltimore; and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems Inc. in Boulder, Colorado; L3Harris Technologies in Rochester, New York; and Teledyne Scientific & Imaging in Thousand Oaks, California.
By Ashley Balzer
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Share
Details
Last Updated Jul 31, 2025 EditorAshley BalzerContactAshley Balzerashley.m.balzer@nasa.govLocationGoddard Space Flight Center Related Terms
Nancy Grace Roman Space Telescope Dark Energy Dark Matter Exoplanets Galaxies Goddard Space Flight Center Nebulae Sensing the Universe & Multimessenger Astronomy Stars The Universe Explore More
7 min read One Survey by NASA’s Roman Could Unveil 100,000 Cosmic Explosions
Article 2 weeks ago 3 min read NASA’s Roman Space Telescope Team Installs Observatory’s Solar Panels
Article 3 weeks ago 6 min read NASA’s Roman Mission Shares Detailed Plans to Scour Skies
Article 3 months ago View the full article
-
By Space Force
Brig. Gen. Paul's appointment marks a major milestone in U.S.-Canada defense collaboration, particularly in the growing domain of space operations.
View the full article
-
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
Keep Exploring Discover More Topics
Commercial Space Stations
Low Earth Orbit Economy
Commercial Space
Humans In Space
View the full article
-
-
Check out these Videos
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.