In the quarter century that humans have lived and worked aboard the International Space Station, astronauts and visitors from around the world have celebrated countless holidays more than 250 miles above Earth while traveling 17,500 miles per hour. Crews have marked Thanksgiving, Christmas and Hanukkah, New Year’s, birthdays, and national holidays as they circle the planet every 90 minutes.  

Holiday traditions in space often look familiar, just adapted for microgravity. NASA astronauts share special meals packed by the Space Food Systems Laboratory at the agency’s Johnson Space Center in Houston, where crews select their menus with help from nutritionists and food scientists before launch. Cargo launches arriving before special occasions often deliver Holiday Bulk Overwrapped Bags filled with foods like clams, oysters, turkey, green beans, and smoked salmon, along with shelf-stable treats such as candies, icing, almond butter, and hummus. 

Crew members exchange small gifts that float through the modules, add festive decorations around the station, and connect with loved ones through video calls. Astronauts also send holiday greetings to Earth, a reminder that even in space, home is never far away. 

Enjoy 25 years of celebrations below. 

The space station remains a vital scientific platform, providing the foundation needed to survive and thrive as humanity ventures into the unexplored territories of our universe.

Learn more about the space station’s 25 years of continuous human presence and explore stories, images, and research at:

https://www.nasa.gov/international-space-station/iss25

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Introduction

In an era where satellite observations of Earth are commonplace, it’s easy to forget that only a few decades ago, the amount of information available about the state of Earth’s environment was limited; observations were infrequent and data were sparsely located.

As far back as the late 1950s, there were primitive numerical weather prediction (NWP) models that could produce an accurate (or what a forecaster would call “skillful”) forecast given a set of initial conditions. However, the data available to provide those initial conditions at that time were limited. For example, the weather balloon network circa 1960 only covered about 10% of the troposphere and did not extend into the Southern Hemisphere, the tropics, or over the ocean.

Weather forecasters of the pre-satellite era typically relied upon manual analysis of plotted weather maps, cloud observations, and barometric pressure readings when making forecasts. They combined this limited dataset with their own experience issuing forecasts in a particular area to predict upcoming weather and storm events. While those pioneering forecasters made the most of the limited tools available to them, poor data – or simply the lack of data – inevitably led to poor forecasts, which usually weren’t accurate beyond two days. This time duration was even less than that in the Southern Hemisphere. As a result, the forecasts issued typically lacked the specificity and lead time required to adequately prepare a community before a snowstorm or hurricane.

Although the first satellite observations (e.g., from the Television Infrared Observation Satellite (TIROS) program or early Nimbus missions) whet forecasters’ appetites for what might be possible in terms of improving weather forecasting, polar orbiting satellites could only observe a given location twice a day. Those snapshots from above were insufficient for tracking rapidly evolving weather phenomena (e.g., thunderstorms, tornadoes, and intensification of hurricanes). Beyond cloud information, forecasters required data on temperature, moisture, and wind profiles in the atmosphere in addition to output from NWP models.

It was the advent of geostationary observations (also called geosynchronous) that truly led to revolutionary advances in weather forecasting. This approach enabled continuous monitoring of the atmosphere over a particular region on Earth. Hence, the development and evolution of NOAA’s Geostationary Operational Environmental Satellites (GOES) has been a major achievement for weather forecasting.

For 50 years, GOES have kept a constant vigil over the Western Hemisphere and monitored the Sun and the near-Earth environment – see Visualization 1. Since 1975, the National Oceanic and Atmospheric Administration (NOAA) and NASA have partnered to advance NOAA satellite observations from geostationary orbit. GOES satellites serve as sentinels in the sky, keeping constant watch for severe weather and environmental hazards on Earth as well as dangerous space weather. This narrative will focus on the development and evolutions of the Earth observing instruments on GOES with a mention of several of the space weather instruments.

Reaching a half-century of operation is a remarkable achievement for GOES, or any mission. The Earth Observer has published several articles chronicling the milestones of Earth observing missions, including The Vanguard of Earth-Observing Satellites [March–April 2019, 31:2, 7–18], Nimbus Celebrates Fifty Years [March–April 2015, 27:2, 18–31], and NASA Participates in Pecora 22 Symposium and Celebrates Landsat 50th Anniversary [Nov.–Dec. 2022, 34:6, 4–9]. This article, reflecting on GOES accomplishments, will join that list.

The article provides the history leading up to the development of GOES and traces the development of GOES from the earliest launch in 1975 to the last launch in late 2024, which completed the GOES–R series – see Figure 1. The article ends with a look at the plans for Geostationary Extended Observations (GeoXO), which seeks to extend the GOES legacy to the middle of the 21^st century, followed by some concluding thoughts.

GOES Heritage Missions: ATS and SMS

The heritage of GOES can be traced to the Applications Technology Satellite (ATS) series, which consisted of a set of six NASA spacecraft launched from December 7, 1966 to May 30, 1974. These missions were created to explore and flight-test new technologies and techniques for communications, meteorological, and navigation satellites. ATS was a multipurpose engineering satellite series, testing technology in communications and meteorological applications from geosynchronous orbit.

ATS satellites aimed to test the theory that gravity would anchor a satellite in a synchronous orbit, 22,300 statute miles (37,015 km) above the Earth. This orbit allowed the satellites to move at the same rate as the Earth, thus seeming to remain stationary. Although the ATS satellites were intended mainly as testbeds, they also collected and transmitted meteorological data and functioned at times as communications satellites. For example, ATS-6, the last in the series, was the first to use an education and experimental direct broadcast system, which is now commonplace on Earth observing satellites (e.g., Terra).

Also included in the ATS payload was a spin-scan camera that Verner Suomi and associates had developed in the early 1960s. The device was so named because it compensated for the motion of the satellite and still obtained clear visible (television-like) photographs. The University of Wisconsin, Madison’s (UWM) Space Science and Engineering Center (SSEC), which Suomi and colleagues at UWM had just recently established, funded the camera’s development and NASA approved its inclusion as part of the ATS payload. The spin-scan camera on ATS-1 produced spectacular full disk images of Earth; a few years later the camera on ATS-3 produced similar images, this time in color.

Although designed primarily to test and demonstrate new technologies, imagery captured by the ATS payload led to some serendipitous science. Analysis of spin-scan camera images, while labor intensive and expensive and not practical for use operationally, led to new discoveries about storm origins that had never before been available. For example, Tetsuya Fujita analyzed ATS camera images of storms in the Midwest United States in 1968 as part of his in-depth studies of tornadoes. This work led to the development of the Fujita Scale for tornado intensity. Also in 1968, “Hurricane Hunter” aircraft data and radar imagery, along with ATS images allowed meteorologists to observe the complete life cycle of Hurricane Gladys. Today, this approach is routine, but at the time it was groundbreaking.

Following the success of the ATS “technology demonstration” series, NASA and NOAA began to develop an operational prototype of the dedicated geosynchronous weather satellite, the Synchronous Meteorological Satellite (SMS). SMS-1 was launched in 1974, with SMS-2 following the next year. Owned and operated by NASA, the SMS satellites were the first operational satellites designed to sense meteorological conditions in geostationary orbit over a fixed location on the Earth’s surface. The ATS spin-scan camera manufacturers – SSEC and Santa Barbara Research – altered their ATS camera design, replacing the television-like photographic apparatus with an imaging radiometer with eight visible and three infrared channels. The revised instrument became known as the Visible and Infrared Spin-Scan Radiometer (VISSR). They also added a telescope that would allow for high-resolution imaging of smaller portions of Earth, allowing researchers to study storm formation in more detail.

First Generation: GOES 1–3

The GOES era began in October 1975 with the launch of GOES-1 (initially called SMS-3). The first three GOES missions were spin-stabilized satellites. The VISSR instrument, initially developed for the SMS missions, became the workhorse instrument for the first generation of GOES missions. VISSR provided high-quality day and night observations of cloud and surface temperatures, cloud heights, and wind fields – see Figure 2.

The early GOES missions also focused on monitoring space weather. The first generation of GOES featured a Space Environment Monitor (SEM) to measure proton, electron, and solar X-ray fluxes as well as magnetic fields around the satellites. This technology became standard on all subsequent GOES satellite missions.

The new satellites quickly began providing critical information about the location and trajectory of hurricanes. The earliest generation of GOES provided crucial data about Tropical Storm Claudette and Hurricane David in 1979 – both of which devastated regions of the United States.

Second Generation: GOES 4–7

The second generation of GOES began in 1980, with the launch of GOES-4. NASA, NOAA, and SSEC collaborated to make further enhancements to the VISSR instrument, adding temperature sounding capabilities. The development of the VISSR Atmospheric Sounder (VAS) was particularly helpful for the study and forecasting of severe storms. While there were sounders on polar orbiting satellites of this era (e.g., TIROS and Nimbus), polar orbiters, which take measurements of the same location twice daily, often missed events that occurred on shorter timescales, such as thunderstorms. By contrast, VAS on GOES could image the same area every half-hour, allowing for more detailed tracking of storms, leading to improved severe storm forecasting and enabling more advanced warning of the storm’s arrival. VAS became the basis for the establishment of an extensive severe storm research program during the 1980s.

The second generation GOES missions were capable of obtaining vertical profiles of temperature and moisture throughout the various layers of the atmosphere. This added dimension gave forecasters a more accurate picture of a storm’s extent and intensity, allowed them to monitor rapidly changing events, and helped to predict fog, frost, and freeze, as well as dust storms, flash floods, and even the likelihood of tornadoes.

The second generation of GOES helped forecasters track and forecast the impacts from the 1982–1983 El Niño event – one of the strongest El Niño–Southern Oscillation (ENSO) events on record that led to significant economic losses. This generation of GOES satellites also gave forecasters vital information about Hurricane Juan in 1985 and Hurricane Hugo in 1989, both destructive storms for areas of the United States – see Figure 3.

GOES-7, launched in 1987, added the new capability of detecting distress signals from emergency beacons. These GOES satellites have helped to rescue thousands of people as part of the Search and Rescue Satellite-Aided Tracking (SARSAT) system developed to detect and locate mariners, aviators, and other recreational users in distress. This system uses a satellite network to detect and locate distress signals from emergency beacons on aircraft and vessels and from handheld personal locator beacons (PLBs) quickly. The SARSAT transponder on GOES immediately detects distress signals from emergency beacons and relays them to ground stations. In turn, this signal is routed to a SARSAT mission control center and then sent to a rescue coordination center, which dispatches a search and rescue team to the location of the distress call.

Third Generation: GOES 8–12

In 1994, advances in two technologies enabled another significant leap forward in capabilities for GOES: improved three-axis stabilization of the spacecraft and separating the imager and sounder into two distinct instruments with separate optics (e.g., GOES Imager and GOES Sounder). Simultaneous imaging and sounding gave forecasters the ability to use multiple measurements of weather phenomena, resulting in more accurate forecasts. Another improvement was flexible scanning, where the satellites could temporarily suspend their routine scans of the hemisphere to concentrate on a small area to monitor quickly evolving events. This capability allowed meteorologists to study local weather trouble spots, improving short-term forecasts.

In 2001, forecasters used GOES-8 to track the slow-moving remnants of Tropical Storm Allison, stalled over the Gulf Coast. During the next four days, Allison dropped more than three feet of rain across portions of coastal Texas and Louisiana, causing severe flooding, particularly in the Houston area.

GOES-12, the final satellite in the third generation, launched in 2001. It included a new Solar X-ray Imager (SXI) as part of its payload. SXI was the first X-ray telescope that could take a full-disk image of the Sun, which enabled forecasters to detect solar storms and better monitor and predict space weather that could affect Earth. Some geomagnetic storms can damage satellites, disrupting communications and navigation systems, impacting power grids, and harming astronauts in space.

Fourth Generation: GOES 13–15

By the mid-2000s, the fourth generation of GOES, known as the GOES-N series, enhanced the mission with improvements to the Image Navigation and Registration subsystem, including star-trackers, to better determine the coordinates of intense storms. Improvements in batteries and power systems allowed this generation to provide continuous imaging. GOES-13 also added an Extreme Ultraviolet Sensor, which monitored ultraviolet emissions from the Sun as well as the solar impact on satellite orbit drag and radio communications.

In April 2011, GOES-13 monitored the record-breaking tornado outbreak that hit the Southeastern United States – see Visualization 2. From April 25–28, 362 tornadoes carved a path across a dozen states, leaving an estimated 321 people dead. In 2012, NOAA operated GOES-14, the on-orbit backup satellite, in a special rapid-scan test mode, providing one-minute imagery of Tropical Storm Isaac and Hurricane Sandy, both destructive storms.

The GOES-R Series: GOES-16–19

NASA launched the first satellite in the GOES-R Series for NOAA in 2016. The GOES-R Series brought new state-of-the-art instruments into orbit, including the Advanced Baseline Imager (ABI), a high-resolution imager with 16 channels, and the Geostationary Lightning Mapper, the first lightning mapper flown in geostationary orbit. The satellites also gained the ability to concurrently provide a full-disk image every ten minutes, a contiguous United States image every five minutes, and two smaller localized images every 60 seconds (or one domain every 30 seconds). For the first time, meteorologists could see the big picture while simultaneously zooming in on a specific weather event or environmental hazard.

The latest GOES satellite series brought revolutionary improvements, providing minute-by-minute information to forecasters, decision-makers, and first responders to give early warning that severe weather is forming, monitor and track the movement of storms, estimate hurricane intensity, detect turbulence, and even spot fires before they are reported on the ground.

The GOES-R Series satellites also carry a suite of sophisticated solar imaging and space weather monitoring instruments. The final satellite in the series, GOES-19, is also equipped with NOAA’s first compact coronagraph (CCOR-1). This instrument images the solar corona (the outer layer of the Sun’s atmosphere) to detect and characterize coronal mass ejections, which can disrupt Earth’s magnetosphere, leading to geomagnetic storms, auroras, and potential disruptions to technology, including electricity and satellite communications.

In 2017, Hurricane Maria knocked out Puerto Rico’s radar just before landfall. With this critical technology disabled and a major hurricane approaching, forecasters used 30-second data from GOES-16 to track the storm in real-time – see Visualization 3. The satellite’s rapid scanning rate allowed forecasters to analyze cloud patterns and understand the evolution of Maria’s position and movement as well as discern the features within the hurricane’s eye to estimate intensity.

The most recent generation of satellites also significantly improved fire detection and monitoring. During California’s Camp Fire in 2018, GOES-16 played a crucial role in monitoring the fire’s progression and smoke plumes, assisting the efforts to contain the fire – see Visualization 4. The satellite provided an extremely detailed picture of fire conditions, quick detection of hot spots, and the ability to track the fire’s progression and spread in real-time. Forecasters used ABI data from GOES-16 to track the fire’s movement and intensity even before ground crews could fully see it due to thick smoke. Not only did the data help firefighters fight the fire more effectively, but it also helped keep firefighters safe during the disaster.

What’s Next? GeoXO

NOAA, NASA, and industry partners are now developing the future generation of geostationary satellites. The Geostationary Extended Observations (GeoXO) will provide continuity of observation from geostationary orbit as the GOES-R series nears the end of its operational lifetime. The first GeoXO launch is planned for launch in the early 2030s.

GeoXO will prioritize and advance forecasting and warning of severe weather. Similar to GOES, the information GeoXO gathers will also be used to detect and monitor environmental hazards (e.g., wildfires, smoke, dust, volcanic ash, drought, and flooding).

The more advanced observing capabilities will allow forecasters to provide earlier warning to decision makers, improve the skillfulness of short-term forecasting, and allow for greater lead times for warnings of severe weather and other hazards that threaten the security and well-being of everyone in the Western Hemisphere well into the 2050s.

Conclusion

For 50 years, GOES satellites have provided the only continuous coverage of the Western Hemisphere. Their data have been the backbone of short-term forecasts and warnings of severe weather and environmental hazards. GOES detect and monitor events as they unfold, providing forecasters with real-time information to track hazards as they happen. They are also part of a global ring of satellites that contribute data to numerical weather prediction models. GOES also monitors the Sun and provides critical data for forecasts and warnings of space weather hazards.

Each successive generation of GOES has brought advancements and new capabilities that have improved the skill of short-term weather forecasts and our ability to prepare for and respond to severe weather and natural disasters. The information the satellites supply is essential for public safety, protection of property, and efficient economic activity. Meteorologists, emergency managers, first responders, local officials, aviators, mariners, researchers, and the general public depend on GOES. Everyone in the Western Hemisphere benefits from GOES data each and every day.

Acknowledgment

The primary source for the information provided in the section on “GOES Heritage Missions” was Conway, Eric: Atmospheric Science at NASA: A History (2008), pp. 140–41.

Michelle Smith
NOAA Satellite and Information Service
michelle.smith@noaa.gov

Alan Ward
NASA’s Goddard Space Flight Center/Global Science & Technology Inc.
alan.b.ward@nasa.gov

Introduction

Launched in Feb. 2024, NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission is a cornerstone of Earth system science designed to deepen our understanding of how these environmental and biological components come together to influence our climate, carbon cycle, and ecosystems. PACE has funded three supporting components: the PACE Postlaunch Airborne eXperiment (PACE–PAX), the third PACE Science and Applications Team (SAT3), and the PACE Validation Science Team (PVST). Each group serves distinct but interdependent roles in advancing the scientific objectives of the mission through product development and rigorous assessment of data quality.

Recognizing the interconnected focus areas among these groups, the organizers consolidated this year’s separate gatherings into one comprehensive event – the “PAC3” meeting. The combined meeting took place from Feb. 18–21, 2025 at NASA’s Goddard Institute for Space Studies (GISS) in New York City, just 10 days after the first anniversary of the PACE launch – see Photo 1 and Photo 2.

The PACE Mission and Payload

PACE’s long-term objectives focus on understanding ocean and terrestrial ecosystem productivity, detecting harmful algal blooms, exploring relationships between aerosols and clouds, and integrating these insights into Earth system science to enhance both research and decision-making capacities. These goals are accomplished by the advanced suite of three complementary instruments.

The Ocean Color Instrument (OCI) is a hyperspectral radiometer that measures ocean ecosystems’ biological, biogeochemical, and physical dynamics by capturing light over hundreds of narrow wavelengths from the deep ultraviolet to the infrared. Additionally, the broad spectral range and spectral resolution of the measurements allow the research community to characterize aerosols, clouds, land surfaces, and trace gases.

The Hyper-Angular Rainbow Polarimeter #2 (HARP2) is a multiangle polarimeter with a wide swath, four visible–near infrared (VIS–NIR) spectral channels, and between 10 and 60 viewing angles (i.e., the hyperangular capability) in each spectral channel. HARP2 is designed for retrieval of cloud and aerosol properties.

The Spectropolarimeter for Planetary Exploration (SPEXone) is also a multiangle polarimeter with different and complementary properties to HARP2. SPEXone has a narrow swath and five viewing angles with a spectral sensitivity of 100 bands from the ultraviolet to the near infrared. It is optimized for the retrieval of aerosol properties.

More details about the PACE mission can be found at its website.

PACE Mission Updates

The PAC3 meeting included a review of the PACE mission’s status and recent developments. This overview included meeting status updates on OCI, SPEXone, and HARP2 from their respective instrument scientists: Gerhard Meister [NASA’s Goddard Space Flight Center (GSFC)], Otto Hasekamp [Space Research Organization, Netherlands (SRON)], and Vanderlei Martins [University of Maryland, Baltimore County (UMBC)]. This section of the meeting covered updates on the early mission data availability and accessibility, including a review of the PACE data website. These details are summarized on the PACE data availability website and the ‘help hub’.

OCI

Meister reported that OCI has exceeded radiometric performance requirements, delivering highly accurate hyperspectral data. He noted that, with the release of Version 3 (V3) data reprocessing, OCI calibration now uses only on-orbit solar diffuser measurements to improve temporal stability. Key improvements of V3 include enhanced corrections for atmospheric absorbing gas effects and updated bidirectional reflectance distribution function (BRDF) parameters. Meister said that analysis of temporal trends has revealed solar diffuser degradation in the ultraviolet range, with ongoing corrections being made. For example, he cited how the team is using the solar diffuser that is only exposed once a month to correct the observations of the solar diffuser that is exposed daily. He also discussed other anomalies, including striping around 10° scan angle, reduced accuracy in the 590–610 nm region and implementation of crosstalk correction to compensate for reduced accuracy of wavelength measurements in the ultraviolet (i.e., for wavelengths shorter than 340 nm).

SPEXone

Hasekamp reported that SPEXone is delivering quality radiometric and polarimetric data. The team has developed the Remote Sensing of Trace Gases and Aerosol Products (RemoTAP) algorithm, an advanced aerosol retrieval algorithm that determines the total atmospheric column of aerosols, aerosol size distribution information, energy absorbed by aerosols, and vertical extent of the aerosol layer. Hasekamp showed that observations demonstrate minimal bias in size distribution retrievals across low aerosol optical depth (AOD) environments and these observations have good agreement with observations from ground-based Sun photometers that are part of the Aerosol Robotic Network (AERONET). He added that future updates will address radiometric calibration discrepancies with OCI.

HARP2

Martins reported that HARP2 continues to perform well and is delivering polarization-sensitive observations of aerosols and clouds. He noted that plans include making continued geolocation and calibration refinements, as well as cross-calibration with OCI and SPEXone to harmonize all the PACE radiometric data products.

PACE Data Access and Website Resources

Several presentations outlined the tools and platforms available to make data from the PACE mission accessible to the broader scientific community.

Alicia Scott [GSFC/Science Applications International Corporation (SAIC)] described capabilities provided by the Ocean Biology Distributed Active Archive Center (OB.DAAC). The OB.DAAC stores and processes data from all PACE instruments using tools, such as Earthdata Search and earthaccess Python libraries that enable user-friendly data retrieval pipelines. Training resources and tutorials are available to streamline usage.

Carina Poulin [GSFC/Science Systems and Applications, Inc (SSAI)] provided an overview of the PACE Data Website, which serves as a central hub for accessing datasets, reprocessing information, and product tutorials. The V3 landing page provides details on calibration updates, validation results, and pathways for integrating PACE data into user workflows.

EarthCARE Mission Updates

Many of PACE’s science objectives dovetail with that of the Earth Clouds, Aerosols, and Radiation Explorer (EarthCARE), a joint venture by the European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA). Hence, the PAC3 meeting included participation from the EarthCARE teams. The EarthCARE observatory has four advanced instruments: a high spectral resolution ATmospheric LIDar (ATLID), a doppler capable Cloud Profiling Radar (CPR), a Multi-Spectral Imager (MSI), and a Broad-Band Radiometer (BBR). The measurements from EarthCARE complement those of PACE and enable cross validation, enriching scientific knowledge of complex Earth system processes. The synergistic nature of these missions also means that validation activities for one are well suited to both. For example, the Plankton, Aerosol, Cloud, ocean Ecosystem Postlaunch Airborne eXperiment (PACE-PAX) field campaign (discussed later in this article) incorporated validation activities for EarthCARE, and EarthCARE funded campaigns have made observations during PACE overpasses.

Rob Koopman [ESA] outlined progress on EarthCARE, including preparation for validation activities as part of ESA and JAXA’s joint efforts. He reported that the mission’s ATLID lidar data products are in excellent alignment with airborne High Spectral Resolution Lidar (HSRL) datasets (flown during PACE-PAX). Koopman showed preliminary results from underflights with NASA aircraft that demonstrate high accuracy for cloud and aerosol retrieval, albeit with some calibration challenges that will require further refinement. He also said that several EarthCARE–PACE mutual validation campaigns are planned to ensure inter-mission consistency across critical science products.

PACE–PAX Sessions

The first component of the PAC3 meeting focused on PACE–PAX, a field campaign conducted in California and adjacent coastal regions during Sept. 2024 – see Figure 1. Kirk Knobelspiesse [GSFC, OEL—PACE Polarimeter Lead, PACE-PAX Mission Scientist], Ivona Cetinić [NASA’s Goddard Space Flight Center (GSFC)/Morgan State University, Ocean Ecology Laboratory (OEL)—PACE Validation Science Team lead, PACE-PAX Deputy Mission Scientist], and Brian Cairns [NASA Goddard Institute for Space Studies (GISS)—PACE Deputy Project Scientist, PACE-PAX Deputy Mission Scientist] led the campaign, which, in addition to personnel from most NASA Centers, had participation from academia (e.g., University of Maryland, Baltimore County), other government agencies (e.g., Naval Postgraduate School and National Oceanic and Atmospheric Administration), and international space agencies (e.g., Space Research Organization, Netherlands).

Campaign Overview

The PACE–PAX mission supported the PACE Science Data Product Validation Plan. This included validation of new PACE and EarthCARE products, data collection during instrument overpasses, verification of radiometric and polarimetric measurements, and targeted investigation of region-specific phenomena (e.g., multilayer aerosols and phytoplankton blooms).

Operational Highlights

PACE–PAX used a diverse array of platforms to collect atmospheric and oceanic data, including aircraft [e.g., NASA Earth Resources-2 (ER-2) and the Naval Postgraduate School’s Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter], research vessels (NOAA’s R/V Shearwater and the 30-foot sailboat R/V Blissfully), and ground-based instruments such as Sun photometers and lidars. Key achievements include 13 ER-2 and 17 Twin Otter science flights, 15 RV Shearwater and 9 R/V Blissfully day cruises. These flights and ocean surveys supported 16 days of observations during a PACE overpass, six days of observations during an EarthCARE overpass, ground vicarious calibration at Ivanpah Playa, CA, numerous overflights of AERONET ground sites. Beyond validation, several unique events were observed that may be of interest for scientific purposes. Intense wildfires (e.g., the Bridge, Airport, and Line fires in 2024) were observed in Southern California in mid-September, while a red tide outbreak was observed later in the month along the Northern California coast – see Figure 2. Additionally, elements of the PVST coordinated their own validation efforts with the PACE–PAX campaign.

Preliminary Findings

Highlights of the PACE-PAX sessions demonstrated:

• validation of EarthCARE and PACE aerosol and cloud products using the HSRL2 on NASA ER-2,
• validation of PACE cloud products using polarimeters operating on the NASA ER-2 and in situ sensors on the CIRPAS Twin Otter,
• numerous successful matchups of hyperspectral data from OCI on PACE with field measurements of chlorophyll-a captured during ship campaigns, and
• observations of diverse phenomena (e.g., marine stratocumulus clouds and transported wildfire aerosols over clouds), which supported the testing of new retrieval algorithms.

The early results show the critical role that validation activities, such as PACE–PAX, play in creating a bridge between orbital science and ground truth.

PACE Science and Application Team (SAT3) Session

SAT3, with a focus on both science and applications, offered a compelling second component of the PAC3 meeting. The Earth Observer has previously reported on PACE applications, most recently in the 2023 article, Preparing for Launch and Assessing User Readiness: The 2023 PACE Applications Workshop [Nov–Dec 2023, 35:6, 25–32]. The SAT3 team convened during PAC3 to explore how PACE data could enhance research in diverse scientific fields and support applied uses for societal benefit. Dedicated sessions provided updates on ongoing NASA-funded projects to retrieve new geophysical variables, improve data assimilation, and refine product development pipelines.

SAT3 teams presented early results including studies that use PACE’s OCI to make pigment-specific absorption measurements, study diatom biomass retrieval, and gather chlorophyll concentration estimation. These studies emphasized new tools for tracking individual phytoplankton groups, such as diatoms and cyanobacteria that are vital for ecosystem research and understanding phytoplankton dynamics. Participants also showcased efforts to develop predictive models for the detection of harmful algal blooms (HABs) and improvement of early warning systems to mitigate public health impacts and economic consequences in both coastal regions and the Great Lakes. Several presentations highlighted new aerosol absorption and scattering measurements that are using polarimetry (i.e., SPEXone and HARP2) and how these findings are being incorporated into models of aerosol–cloud radiative forcing. Presenters also described how machine learning tools can integrate PACE measurements into Earth system models, through innovations in data assimilation, with promising results for global climate monitoring.

The SAT3 discussions highlighted PACE’s potential to impact disciplines ranging from oceanography to climate science.

PACE Validation Science Team Sessions

Sessions dedicated to the PACE PVST emphasized the ongoing role of PVST initiatives in confirming the reliability, accuracy, and long-term stability of PACE data products. Topics of focus for the PVST group included algorithm development and validation, cross-mission synergies, field-based campaign integration, and cloud products.

Some of the presenters shared updates on validation pipelines for radiometric and polarimetric products, with an emphasis on comparing against well-characterized datasets from AERONET Sun photometers, HSRL, and the Pan-and-Tilt Hyperspectral Radiometer (PANTHR) developed by Vlaams Instituut voor de Zee (VLIZ), or the Flanders Marine Institute, Belgium – see Photo 3. This radiometer was installed on a 30-m (~98-ft) tower in the Chesapeake Bay in May 2024 and is part of WATERHYPERNET network, which seeks to provide time series of hyperspectral water reflectance data from oceanic, coastal, and inland waters for the validation of satellite data at all wavelengths in the range 400–900 nm.

Reports from PVST members highlighted how data from PACE–PAX campaigns and satellite overpasses are contributing to the validation of error budgets developed prelaunch and refined uncertainty characterization. Other presentations highlighted the development of validation strategies for PACE-derived cloud properties, including cloud optical thickness, top height, and droplet size distributions with significant contributions from EarthCARE observations. Ocean observation validation was represented as well, with presentations from many groups that are focusing on retrieval of not only oceanic optical properties but biological components. This data offers crucial validation for the advanced phytoplankton composition and general ocean productivity products from PACE.

The PVST’s work continues to provide the foundation for confidence in PACE data products. Their accuracy ensures broad usability of those products across global science applications.

Conclusion

The PAC3 meeting, held at NASA’s GISS, highlighted the collective efforts of the PACE mission’s diverse teams to address a broad range of Earth system science challenges. By combining the meetings for PACE–PAX, SAT3, and PVST, participants were able to strengthen collaborations, align ongoing efforts, and lay the groundwork for future research and validation activities.

Roundtable discussions and team updates also revealed the critical role of PACE in addressing long-standing Earth system science questions, such as understanding the influence of aerosols on cloud formation and characterizing the impacts of oceanic changes on global biogeochemical cycles at a global scale. The meeting concluded with participants compiling action items for further exploration. Topics identified for future efforts included strategies for ensuring long-term data calibration, improving data delivery pipelines, and refining algorithm development processes.

This meeting was one of the last significant events hosted at GISS before the facility’s closure at the end of May 2025. The findings and outcomes from PAC3 continue to inform and inspire PACE mission science, further enhancing its importance in advancing our understanding of the Earth system.

Kirk Knobelspiesse
NASA’s Goddard Space Flight Center
kirk.d.knobelspiesse@nasa.gov 

Cecile S. Rousseaux
NASA’s Goddard Space Flight Center
cecile.s.rousseaux@nasa.gov

Ivona Cetinić
NASA’s Goddard Space Flight Center/Morgan State University
ivona.cetinic@nasa.gov

Andrew Sayer
NASA’s Goddard Space Flight Center
andrew.sayer@nasa.gov