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By European Space Agency
ESA Open Days 2025
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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
Curiosity Navigation Curiosity Home Mission Overview Where is Curiosity? Mission Updates Science Overview Instruments Highlights Exploration Goals News and Features Multimedia Curiosity Raw Images Images Videos Audio Mosaics More Resources Mars Missions Mars Sample Return Mars Perseverance Rover Mars Curiosity Rover MAVEN Mars Reconnaissance Orbiter Mars Odyssey More Mars Missions Mars Home 2 min read
Curiosity Blog, Sols 4597-4599: Wide Open Spaces
NASA’s Mars rover Curiosity acquired this image, of the sweeping Mount Sharp vista into which the rover will drive the weekend of July 11-12, 2025, using its onboard Left Navigation Camera. Curiosity captured the image on July 11, 2025 — Sol 4596, or Martian day 4,596 of the Mars Science Laboratory mission — at 12:01:55 UTC. NASA/JPL-Caltech Written by Michelle Minitti, MAHLI Deputy Principal Investigator, Framework
Earth planning date: Friday, July 11, 2025
Imagine this vista as the view out your office window to start your workday. Your natural tendency would be to grab your camera and photograph as much of the view as possible. Curiosity was lucky enough to find herself in this situation today after a successful drive of about 61 meters (about 200 feet) on Wednesday, and the science team operating Curiosity wasted no time papering the scene with mosaics.
Between Mastcam and ChemCam, we planned 105 images across the scene. Those images will capture the structures underpinning the boxwork ridges we are driving toward, smaller-scale fractures in the near field that might be related to the boxwork ridges, and the back side of a ridge we recently studied in detail, “Volcán Peña Blanca.” Together, the images will help us understand the geologic history of the area that hosts the boxwork ridges, and what conditions existed in this part of Mount Sharp to support their formation.
We did not neglect the rocks directly in front of the rover as we gazed at our surroundings. Indeed, the bedrock near the rover was nearly uniformly packed with small (less than 1 centimeter, or 0.39 inches) rounded nodules, a characteristic we have not seen for awhile. MAHLI will image three different instances of the nodules while APXS and ChemCam will each analyze two different targets to understand the chemistry of the nodules and the bedrock hosting them.
REMS, RAD, and DAN will continue to monitor the Martian environment and subsurface throughout the weekend. Additionally, we planned multiple observations of dust devils, the amount of dust in the atmosphere, and clouds including a cloud movie timed to match the overflight of the CASSIS instrument. Our drive will take us to the foot of the smooth slope seen in the distance of the above image. That slope is the ramp we will take to the top of a big boxwork structure, where surely other delightful vistas await.
For more Curiosity blog posts, visit MSL Mission Updates
Learn more about Curiosity’s science instruments
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Last Updated Jul 16, 2025 Related Terms
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Explore This Section Science Uncategorized NASA SCoPE Summer Symposium… Overview Learning Resources Science Activation Teams SME Map Opportunities More Science Activation Stories Citizen Science 4 min read
NASA SCoPE Summer Symposium Celebrates Early Career Scientists and Cross-Team Collaboration
From June 16–18, 2025, the NASA Science Mission Directorate Community of Practice for Education (SCoPE) Summer Symposium brought together a community of scientists, educators, and outreach professionals to celebrate and strengthen NASA’s commitment to developing its workforce and broadening participation in science.
NASA SCoPE is a NASA-funded initiative at Arizona State University that connects early career scientists with NASA Science Activation (SciAct) program teams to build capacity in science communication, community engagement, and educational outreach. Through targeted support like Seed Grants, Travel Grants, and Mission Liaison opportunities, SCoPE equips scientists with the skills and networks needed to meaningfully engage the public with NASA science.
Held in collaboration with key SciAct teams—including Infiniscope, Co-creating with Communities, NASA’s Community College Network, and NASA’s Universe of Learning—the 2025 symposium highlighted the incredible impact of SCoPE over the past four and a half years. The program has financially supported more than 100 early career scientists across a growing network of nearly 1,000 participants.
Over the course of the three-day event, 23 awardees of SCoPE Seed Grants, Travel Grants, and Mission Liaison Grants came together to share their work, connect across disciplines, and explore new avenues for collaboration. Twelve Seed Grant awardees presented their projects, illustrating the transformative power of partnerships with SciAct teams. Highlights included learning how to write for young audiences through mentorship from NASA eClips in support of the children’s book ‘Blai and Zorg Explore the Moon’, designed for elementary learners; a collaborative effort between ‘Lost City, Icy Worlds’ and OpenSpace that evolved into long-term networking and visualization opportunities; and an Antarctic research project that, through collaboration with the Ocean Community Engagement and Awareness using NASA Earth Observations and Science (OCEANOS) project and Infiniscope, both expanded training opportunities for expedition guides and brought polar science to Puerto Rican high school summer interns.
Beyond formal sessions, the symposium embraced community building through shared meals, informal networking, and hands-on experiences like a 3D planetarium show using OpenSpace software, a telescope demonstration with 30 high school students, and a screening of NASA’s Planetary Defenders documentary. Workshop topics addressed the real-world needs of early career professionals, including grant writing, logic model development, and communicating with the media.
Survey responses revealed that 95% of attendees left with a stronger sense of belonging to a community of scientists engaged in outreach. Participants reported making valuable new connections—with peers, mentors, and potential collaborators—and left inspired to try new approaches in their own work, from social media storytelling to designing outreach for hospital patients or other specialized audiences.
As one participant put it, “Seeing others so passionate about Science Communication inspired me to continue doing it in different ways… it feels like the start of a new wave.” Another attendee remarked, “I want to thank the entire team for SCoPE to even exist. It is an incredible team/program/resource and I can’t even imagine the amount of work, dedication and pure passion that has gone into this entire project over the years. Although I only found SCoPE very recently, I feel like it has been incredibly helpful in my scientific journey and I only wish I had learned of the program sooner. Thank you to the entire team for what was a truly educational and inspirational workshop, and the wonderful community that SCoPE has fostered.”
This successful event was made possible through the dedication of NASA SciAct collaborators and the leadership of SciAct Program Manager Lin Chambers, whose continued support of early career engagement through SCoPE has created a growing, connected community of science communicators. The SCoPE Summer Symposium exemplifies how cross-team collaboration and community-centered design can effectively amplify the reach of NASA science.
Learn more about how NASA’s Science Activation program connects NASA science experts, real content, and experiences with community leaders to do science in ways that activate minds and promote deeper understanding of our world and beyond: https://science.nasa.gov/learn/about-science-activation/
SCoPE-funded scientists and collaborators gather at the 2025 SCoPE Summer Symposium to celebrate program success, share ideas, build partnerships, and advance science communication and education efforts across NASA’s Science Activation program. Share
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Last Updated Jul 15, 2025 Editor NASA Science Editorial Team Related Terms
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