It is with a heavy heart that I announce that NASA Earth Science Communications has directed The Earth Observer to conduct an orderly shutdown of the publication. No new content will be published after Dec. 31, 2025.
While the sunset of The Earth Observer is bittersweet for our team, the good news is that all of the rich historical and descriptive content preserved on The Earth Observer’s archives page will remain accessible to the world. If you’ve never checked this page out, I highly encourage you to do so. You’ll find all of our archived issues saved in a PDF format, and – if you scroll down the page – you’ll find an annotated bibliography with links to numerous entries about a variety of topics to provide the historic context of the progress and accomplishments of the Earth Observing System (EOS).
–Alan Ward, Executive Editor, The Earth Observer
More than 36 years ago, in March 1989, the first issue of The Earth Observer newsletter was released – see Figure 1. The three-page document contained one article that explained the rationale for the National Oceanic and Atmospheric Administration (NOAA) forgoing earlier plans to place instruments on NASA’s first EOS polar platform – at that time envisioned as one of several large platforms operated by NASA, NOAA, Europe, and Japan, with numerous instruments on each platform. Along with this article, that first issue featured an EOS launch schedule, a list of publications and acronyms, and a personals section. Yes; personals. It’s hard to believe that a NASA newsletter would feature personals, but remember that this first issue was published at a time before the internet was widely available. The newsletter served as a bridge to quickly connect hundreds of newly chosen EOS investigators scattered worldwide with the latest EOS program developments. The content of early issues included the latest reports from Investigators Working Group meetings, payload panel reviews, and instrument science team meetings. In short, before the Web, The Earth Observer was the thread that kept the various EOS teams connected.
The history of The Earth Observer is intimately intertwined with the development of EOS; it is difficult to speak of one entity without discussing the other. Over the years, as EOS grew from an idea into actual spacecraft and instruments launching and flying in space, the newsletter began chronicling their journey. Early issues of The Earth Observer describe – often in meticulous detail – the meetings and deliberations during which the EOS concept evolved through various revisions and restructuring before the first EOS mission took flight. In the end, NASA launched three mid-sized “flagship” missions (about the size of a small bus) that became known as Terra (1999), Aqua (2002), and Aura (2004) and complemented their measurement capabilities with numerous other small-to-mid-sized missions. The result is the Earth-observing fleet in orbit above us today. Many of these missions fly in polar, low Earth, or geosynchronous orbit, while several others observe the Earth from the perspective of the International Space Station (ISS) – see Figure 2.
EOS missions are known for their longevity; many missions (and their follow-ons) have long outlived their anticipated life cycle. Each of these missions beam back reams of raw data that must be processed and stored so that it can be accessed and used as input to computer models and scientific studies to understand past environmental conditions, place our current situation in the proper context, and make predictions about the future path our planet could follow.
During its 36-year run, The Earth Observer has borne witness to the successes, failures, frustrations, and advancements of EOS, and of the broader Earth Science endeavors of NASA and its domestic and international partners. Given that publication of this final content marks the end of an era, the newsletter team felt it appropriate to offer some perspective on the newsletter’s contribution. The feature that resulted focuses on the relationship between The Earth Observer and EOS – with specific emphasis on our reporting on satellite missions. See the online article, The Earth Observer: Offering Perspectives from Space Through Time, to learn more.
One of the final items published focuses on Terra, the first EOS flagship, which launched into the night sky on Dec. 18, 1999 from Vandenberg Space Force (then Air Force) Base (VSFB) in California on what was designed as a six-year mission of discovery. Terra’s payload included five instruments – Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Clouds and the Earth’s Radiant Energy System (CERES), Measurement of Pollution in the Troposphere (MOPITT), Multi-angle Imaging SpectroRadiometer (MISR), and Moderate Resolution Imaging Spectroradiometer (MODIS) – intended to collect data that would fill in gaps in our knowledge of the Earth System (as it stood on the cusp of the 21st century, when Terra launched) and in particular, about how land interacts with the atmosphere on a regional and continental scale. The mission also focused on measuring key planetary characteristics needed to understand Earth’s changing environment (e.g., albedo, roughness, evaporation rate, and photosynthesis). The goal was to provide a holistic approach to address larger scientific questions. For more than 26 years, Terra has trained her five instruments toward Earth and gathered data to address wildfires, flooding, hurricanes, and polar ice.
As 2020 drew to a close, in order to conserve enough fuel for the end of the mission, NASA Headquarters decided it was time to for Terra to stop conducting the periodic maneuvers to maintain its 10:30 AM equator crossing. After ceasing maneuvers, the satellite began to drift, which Terra (and the other flagships) have done for the past few years. As Terra’s life draws to a close, it continues to ignite the imagination of the next generation of scientists to catapult the study of our planet for generations to come. Refer to the article, Terra: The End of An Era, to learn more about the feat of engineering that has kept the satellite gathering data two decades past the end of its “Prime Mission” and the key scientific achievements that have resulted.
Since 1997, six CERES instruments have been launched on the EOS and the Joint Polar Satellite System (JPSS) platforms, including the Tropical Rainfall Measuring Mission (TRMM), Terra [2], Aqua [2], the Suomi National Polar-orbiting Platform (Suomi NPP), and the Joint Polar Satellite System–1 (JPSS-1, now named NOAA–20) mission and used to study Earth’s radiation budget (ERB) – the amount of sunlight absorbed by Earth and the amount of infrared energy emitted back to space – that has a strong influence on climate. Researchers pair measurements from CERES instruments with information gathered from other sources to clarify ERB. While the latency of CERES data prevents it from being used for weather forecasting directly, the information on ERB can be used to verify the radiation parameterization of computer models used to make weather forecasts and make predictions about future climate conditions. The ERB data can also be applied to other science research and applications that benefit society. As an example, researchers have used this data to accurately detail changes in the movement of energy from Earth – especially the role that clouds and aerosols play in Earth’s energy budget. The CERES Science Team has a long history of recording proceedings of their meetings in The Earth Observer. It is thus appropriate that a CERES STM summary should be among the last items published this newsletter. Read more about the current status of CERES in space in the article, The State of CERES: Updates and Highlights.
NOAA and NASA have partnered in many endeavors together. The Earth Observer has reported on these collaborations over the years. One well known example is the two agency’s partnership to develop and launch the Geostationary Operational Environmental Satellites (GOES). This mission has become the backbone of short-term forecasts and warnings of severe weather and environmental hazards. The first satellite, GOES-1, launched in 1975; the most recent, GOES-19, launched in 2024. The technology onboard has improved exponentially over the past five decades. The article, Sentinels in the Sky: 50 Years of GOES Satellite Observations, describes this progression of GOES satellites, highlights some of the data obtained, and provides insights into each of these incremental advancements over the past 50 years in this satellite series.
Turning now to a more recent launch, the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite continues to operate nominally. The data PACE returns allow the scientific community to explore the Earth’s ocean, atmosphere, and land surfaces. In February 2025 (10 days prior to the first anniversary of the mission’s launch), the PACE community gathered at NASA’s Goddard Institute for Space Studies (GISS) for the PAC3 meeting, which was so named because it combined three PACE-related activities: the PACE Postlaunch Airborne eXperiment (PACE–PAX), the third PACE Science and Applications Team (SAT3), and the PACE Validation Science Team (PVST). The PAC3 meeting included updates the key instruments on the satellite: the Ocean Color Instrument (OCI), the Hyper-Angular Rainbow Polarimeter–2 (HARP2), and the Spectropolarimeter for Planetary Exploration (SPEXone).
In addition to reporting on PACE, participants during the meeting gave updates on the latest news about the Earth Cloud Aerosol and Radiation Explorer (EarthCARE) observatory, including preparation for validation activities as part of the joint efforts of the European Space Agency (ESA) and Japan Aerospace eXploration Agency (JAXA). The article also details operational highlights, including validation and aerosol products and cloud products. Several Science and Applications Team (SAT3) groups presented results from studies using PACE data and PACE validation studies. The PACE Science Team will continue to monitor Earth and have identified strategies to continue the long-term data calibration and algorithm refinement to ensure the ongoing delivery of information to the research community. The article, Keeping Up with PACE: Summary of the 2025 PAC3 Meeting, provides a full summary of this event.
On Nov. 16, 2025, the Sentinel-6B mission launched from VSFB. The newest satellite in NASA’s Earth observing fleet measures sea levels with an accuracy of one inch every second, covering 90 percent of the oceans every 10 days. It will also contribute the record of atmospheric temperature and humidity measurements. These data are beneficial in observing movement of surface currents, monitoring the transfer of heat through the oceans and around the planet, and tracking changes in water temperature. Sentinel-6B will carry several instruments on this mission, including a radar altimeter, an advanced microwave radiometer, and a radio occultation antenna. The satellite’s observations will be paired with information from other spacecraft to provide detailed information about Earth’s atmosphere that will contribute high-resolution data for computer models to improve weather forecasting.
Sentinel-6B is another shining example of successful collaboration between NASA and NOAA, along with several European partners – ESA, the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), Centre National d’Études Spatiales (CNES), and the European Commission.
Sentinel-6B has publicly released an image showing some of its first observations since launch. The map shows sea levels across a vast stretch of the eastern seaboard and Atlantic Ocean – see Figure 3. The image combines data from Sentinel–6B and its “twin” Sentinel-6 Michael Freilich, which launched in 2020. The data were obtained on Nov. 26, 2025 – just ten days after Sentinel-6B launched.
Together, Sentinel-6B and Sentinel-6 Michael Freilich make up the Copernicus Sentinel-6/Jason- Continuity of Service (CS) mission developed by NASA, ESA, EUMETSAT, and NOAA. Sentinel–6/Jason CS continues a series of ocean surface topography missions that began three decades ago with the NASA/CNES Ocean Topography Experiment (TOPEX)/Poseidon mission. The article, Sentinel-6B Extends Global Ocean Height Record, provides an overview of this latest addition to the NASA and to the international Earth observing fleet.
In the July–September 2025 posting of “The Editor’s Corner,” we reported on the successful launch of the joint NASA–Indian Space Research Organization (ISRO) Synthetic Aperture Radar (NISAR) mission on July 30, 2025 from the Satish Dhawan Space Centre on India’s southeastern coast aboard an ISRO Geosynchronous Satellite Launch Vehicle (GSLV) rocket 5. Soon after launch, NISAR entered its Commissioning phase to test out systems before science operations begin. A key milestone of that phase was the completion of the deployment of the 39-ft (12-m) radar antenna reflector on Aug. 15, 2025. A few days later, on Aug. 19, 2025, NISAR obtained its first image and on Nov. 28, 2025, ISRO made the image (and others) publicly available – see Figure 4.
During the Commissioning phase the S-band Synthetic Aperture Radar (SAR) has been regularly obtaining images over India and over global calibration-validation sites in various payload operating configurations. Reference targets such as Corner reflectors were deployed around Ahmedabad, Gujarat, and a few more locations in India for calibration of the images. Data acquired over Amazon rainforests were also used for calibration of spacecraft pointing and images. Based on this, payload data acquisition parameters have been fine-tuned resulting in high-quality images. The initial images have scientists and engineers excited about the potential of using S-band SAR data for various targeted science and application areas like agriculture, forestry, geosciences, hydrology, polar/Himalayan ice/snow, and oceanic studies.
NISAR has not one but two radars onboard. The S-band radar, described above, is India’s contribution to the mission; the L-band radar is NASA’s contribution. The L-band radar has also been active during the first few months of NISAR’s mission acquiring images of targets in the United States. Karen St. Germain [NASA HQ—Director of Earth Science Division] gave the opening presentation on the Hyperwall at NASA’s exhibit during the Fall 2025 meeting of the American Geophysical Union (AGU) in New Orleans, LA on Dec. 15, 2025. Her presentation, which can be viewed on YouTube, has a section on NISAR that begins at approximately 5:33 time stamp on the video and includes several examples of novel applications made possible by NISAR’s L-band SAR imaging capabilities.
During her AGU presentation, St. Germain also showed recent examples of data from the Surface Water Ocean Topography (SWOT) mission [at timestamp 0:03 on YouTube], highlighting its surface water mapping capabilities, and from PACE [at timestamp 3:34], highlighting its aerosol and biological monitoring capabilities. These missions not only detect aerosol plumes and phytoplankton blooms, but are also able to tell what type they are. She briefly mentioned the Sentinel-6B launch [see timestamp 14:02], teasing her presentation at the Town Hall meeting to be held the next day, where she officially unveiled the Sentinel-6B “first light” image shown as Figure 2 in this editorial.
To conclude, The Earth Observer staff claims a moment of editorial privilege. In a way, we conclude where The Earth Observer began, by sending a “personal message” to all the scientists, engineers, educators, and others – both past and present – who have contributed to EOS and other NASA Earth Science programs that have been covered in this newsletter.
We would like to thank all of the NASA and other leaders, team members, scientists, technicians, students, and staff who have shared your stories over the decades. This publication would not have been the success that it was for so many years without the sustained contributions of the NASA and broader Earth Science community. To all those who volunteered their time to contribute to The Earth Observer over the years, offering your reviews, your subject matter expertise, and your collaboration, we say: “Thank you.” It has been an utmost pleasure to be at the forefront of reporting on the emerging results from your endeavors and bringing this information to the EOS community. We wish you all the best in whatever comes next. While we are saddened to lose the opportunity to continue to share your successes with the Earth Science community via The Earth Observer, we will continue to cheer on your effort and look for future opportunities to publicize your successes however we can.
Barry Lefer
Associate Director of Research, Earth Science Division