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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 21 min read
A Decade of Global Water Cycle Monitoring: NASA Soil Moisture Active Passive Mission
Introduction
The NASA Soil Moisture Active Passive (SMAP) mission, launched in 2015, has over 10 years of global L-band radiometry observations. The low frequency [1.4 GHz frequency or 21 cm (8 in) wavelength] measurements provide information on the state of land surfaces in all weather conditions – regardless of solar illumination. A principal objective of the SMAP mission is to provide estimates of surface soil moisture and its frozen or thawed status. Over the land surface, soil moisture links the water, energy, and carbon cycles. These three cycles are the main drivers of regional climate and regulate the functioning of ecosystems.
The achievement of 10 years in orbit is a fitting time to reflect on what SMAP has accomplished. After briefly discussing the innovative measurement approach and the instrument payload (e.g., a radiometer and a regrettably short-lived L-band radar), a significant section of this article is devoted to describing the mission’s major scientific achievements and how the data from SMAP have been used to serve society (e.g., applied sciences) – including SMAP’s pathfinding role as Early Adopters. This content is followed by a discussion of how SMAP has dealt with issues related to radio frequency interference in the L-Band region, a discussion of the SMAP data products suite, future plans for the SMAP active–passive algorithm, and a possible follow-on L-band global radiometry mission being developed by the European Union’s Copernicus Programme that would allow for data continuity beyond SMAP. This summary for The Earth Observer is excerpted from a longer and more comprehensive paper that, as of this article’s posting, is being prepared for publication in the Proceedings of the Institute of Electrical and Electronics Engineers (IEEE).
SMAP Measurement Approach and Instruments
The SMAP primary and operating instrument is the L-band radiometer, which collects precise surface brightness temperature data. The radiometer includes advanced radio frequency interference (RFI) detection and mitigation hardware and software. The radiometer measures vertical and horizontal polarization observations along with the third and fourth Stokes parameters (T3 and T4) of the microwave radiation upwelling from the Earth. The reflector boom and assembly, which includes a 6 m (20 ft) deployable light mesh reflector, is spun at 14.6 revolutions-per-minute, which creates a 1000 km (621 mi) swath as the SMAP satellite makes its Sun-synchronous orbit of the Earth – see Figure 1. This approach allows coverage of the entire globe in two to three days with an eight-day exact repeat. The radiometer instrument is calibrated monthly by pointing it to the deep sky.
Figure 1. An artist’s rendering of the SMAP Observatory showing both the radiometer and radar. Figure credit: NASA/Jet Propulsion Laboratory/California Institute of Technology The original SMAP instrument design included a companion L-band radar, which operated from April through early July 2015, acquiring observations of co- and cross-polarized radar backscatter at a spatial resolution of about 1 km (0.6 mi) with a temporal revisit of about three days over land. This data collection revealed the dependence of L-band radar signals on soil moisture, vegetation water content, and freeze thaw state. The radar transmitter failed on July 7, 2015. Shortly thereafter, the radar receiver channels were repurposed to record the reflected signals from the Global Navigation Satellite System (GNSS) constellation in August 2015, making SMAP the first full-polarimetric GNSS reflectometer in space for the investigation of land surface and cryosphere.
Scientific Achievements from a Decade of SMAP Data
A decade of SMAP soil moisture observations have led to a plethora of scientific achievements. The data have been used to quantify the linkages of the three main metabolic cycles (e.g., carbon, water, and energy) on land. They have also been used to improve drought assessments and flood prediction as well as the accuracy of numerical weather prediction (NWP) models. They are also used to measure liquid water and thickness of ice sheets, and sea surface salinity. The subsections that follow describe how SMAP data are being put to use in myriad ways that benefit society.
Quantifying Processes that Link the Terrestrial Water, Energy, and Carbon Cycles
The primary SMAP science goal is to develop observational benchmarks of how the water, energy, and carbon cycles link together over land. Soil moisture is the variable state of the land branch of the water cycle. It links the water cycle to the energy cycle through limiting latent heat flux – the change in energy as heat exchanges when water undergoes a phase change, such as evapotranspiration at the land–atmosphere interface. Soil moisture also links the water and carbon cycles, which is evident through plant photosynthesis. SMAP global observations of soil moisture fields, in conjunction with remote sensing of elements of the energy and carbon cycles, can reveal how these three cycles are linked in the real world as a benchmark for weather and Earth system models.
Photosynthesis is down-regulated by both the deficit in water availability and the lack of an adequate amount of photosynthetically active radiation. Global maps reveal how soil moisture and light regulate photosynthesis – see Figure 2. These benchmark observational results can be used to assess how Earth system models link to the three main metabolic cycles of the climate system.
Figure 2. Observed regulation of photosynthesis by water availability [left] and light availability [right]. Blue denotes greater limitation. Photosynthesis rates for both maps determined using solar-induced fluorescence (SIF) measurements (mW/m2 nm sr) from the Tropospheric Ozone Monitoring Instrument (TROPOMI) on the European Union’s Copernicus Sentinel-5P mission. Water availability was determined using soil moisture (SM) measurements from the Soil Moisture Active Passive (SMAP) mission. Light availability was determined using measurements of photosynthetically active radiation (PAR) from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua platforms. The resulting maps show the model slope (mW/m2/nm/sr) of the estimated SIF-SM relationship in the water-limited regime [left] and the model slope (10-3/nm/sr) of estimated SIF-PAR relationship in the light-limited regime [right]. Figure credit: Jonard et al (2022) in Biogeosciences Development of Improved Flood Prediction and Drought Monitoring Capability
SMAP products have also been widely used in applied sciences and natural hazard decision-support systems. SMAP’s observation-based soil moisture estimates offer transformative information for managing water-related natural hazards, such as monitoring agricultural drought – defined as a persistent deficit in soil moisture – and flood volumes – defined as the landscape’s water absorption capacity during precipitation events. The SMAP project produces a parallel, near-real-time data stream that is accessed by a number of federal and state agencies in decision-support systems related to drought monitoring, food security, and landscape inundation and trafficability.
Enhancing Weather and Climate Forecasting Skill
SMAP’s enhancement of numerical weather prediction, model skill, and reduction of climate model projection uncertainties is based on the premise of the contribution of solar energy to weather and climate dynamics. Soil moisture has a strong influence on how available solar energy is partitioned into components (e.g., sensible heat flux versus latent heat flux) over land. The influence propagates through the atmospheric boundary layer and ultimately influences the evolution of weather.
To give an example, land surface processes can affect the evolution of the U.S. Great Plains low-level jets (GPLLJs). These jets drive mesoscale convective weather systems. Previous studies have shown that GPLLJs are sensitive to regional soil moisture gradients. Assimilation of SMAP soil moisture data improves forecasts of weakly synoptically forced or uncoupled GPLLJs compared to forecasts of cyclone-induced coupled GPLLJs. For example, the NASA Unified Weather Research and Forecasting Model, with 75 GPLLJs at 9 km (5.6 mi) resolution both with and without SMAP soil moisture data assimilation [SMAP data assimilation (DA) and no-DA respectively], shows how the windspeed mean absolute difference between SMAP DA and no-DA increase approximately linearly over the course of the simulation with maximum differences at 850 hPa (or mb) for the jet entrance and core – see Figure 3.
Figure 3. The impact of adding soil moisture data [SMAP data assimilation (DA) minus no-DA] to a model simulation from theNASA Unified Weather Research and Forecasting Model (NU-WRF)) of the Great Plains Low Level Jet (GPLLJ). The results show the mean over 75 independent GPLLJ events. The plots correspond to wind speed difference with height (y-axis) and time (hours on x-axis). The panels are for jet entrance [left], jet core [middle] and jet exit [right]. Soil moisture data assimilation enhances the intensity of the simulated GPLLJ. The stippling corresponds to 99% statistical confidence. Figure credit: Ferguson (2020) in Monthly Weather Review Measuring Liquid Water Content and Thickness of Ice Sheets
The mass loss of Greenland and Antarctica ice sheets contributes to sea-level rise – which is one of the most impactful and immediate damaging consequences of climate change. The melt rates over the last few years have raised alarm across the globe and impact countries with coastal communities. The cryosphere community has raised a call-to-action to use every observing system and model available to monitor the patterns and rates of land ice melt.
Surface melt affects the ice cap mass loss in many ways: the direct melt outflow from the ablation zone of the Greenland ice sheet, the structural change of the percolation zone of the Greenland ice sheet, changes in the melt water retention and outflow boundaries, changes in the structure of the Antarctic ice shelves, and destabilization of the buttressing of the glacier outflow through various processes (e.g., hydrofracturing and calving). The long-term climate and mass balance models rely on accurate representation of snow, firn, and ice processes to project the future sea level.
The SMAP L-band radiometer has relatively long wavelength [21 cm (8 in)] observations compared to other Earth-observing instruments. It enables the measurement of liquid water content (LWC) in the ice sheets and shelves as it receives the radiation from the deep layers of the snow/firn/ice column. Relatively high LWC values absorb the emission only partially, making the measurement sensitive to different liquid water amounts (LWA) in the entire column. Figure 4 shows the cumulative LWA for 2015–2023 based on SMAP measurements.
Figure 4. Total annual sum of SMAP daily liquid water amount (LWA) for 2015–2023. The black solid line on each map represents grid edges, and the grey color mask inside the ice sheet indicates melt detections by decreasing brightness temperature. Figure Credit: Andreas Colliander [Finnish Meteorological Institute]. The SMAP L-band radiometer has also been used to derive the thickness of thin sea ice [Soil Moisture and Ocean Salinity (SMOS) mission have been recalibrated to SMAP, using the same fixed incidence angle. The data show strong agreement and demonstrate clear benefits of a combined dataset. The L-band thin ice thickness retrievals provide a useful complement to higher-resolution profiles of thicker ice obtained from satellite altimeters (e.g. ESA’s CryoSat-2 and NASA’s Ice, Clouds and land Elevation Satellite–2 missions).
Extending and Expanding the Aquarius Sea Surface Salinity Record
The joint NASA/Argentinian Aquarius/Satélite de Aplicaciones Científicas (SAC)-D (Aquarius), which operated from 2011–2015, used an L-band radiometer and an L-band scatterometer to make unprecedented monthly maps of global sea surface salinity at 150-km (93-mi) resolution. The SMAP L-band radiometer has not only extended the sea surface salinity record in the post-Aquarius period, it has also increased the spatial resolution and temporal frequency of these measurements because of its larger reflector and wider swath. The increased resolution and revisit allow new and unprecedented perspectives into mixing and freshwater events, coastal plume tracking, and other more local oceanic features.
Providing New Perspectives on Global Ecology and Plant Water Stress
The L-band vegetation optical depth (VOD) – which is related to water content in vegetation – has been retrieved simultaneously with soil moisture using SMAP’s dual-polarized brightness temperatures and is being used to better understand global ecology. Water in above-ground vegetative tissue attenuates and thus depolarizes surface microwave emission, and VOD quantifies this effect. SMAP can provide global observations of VOD in all weather conditions with a two to three day temporal frequency. Changes in VOD indicate either plant rehydration or growth. Ecologists benefit from this new ecosystem observational data, which augments optical and near-infrared vegetation indices [e.g., leaf area index (LAI)] and has a higher temporal frequency that is not affected by clouds and does not saturate as rapidly for dense vegetation.
Examples of how the data have been used include deciphering the conditions when vegetation uptakes soil water only for rehydration (i.e., VOD increase with no LAI change) compared to plant growth (i.e., increase in both VOD and LAI). The applications of VOD are increasing and the ecology community views this product as a valuable additional perspective on soil–plant water relations.
At the moment, this measurement has no ground-based equivalent. Therefore, field experiments with airborne instruments and ground sampling teams are needed to firmly establish the product as a new observational capability for global ecology.
Applied Science Collaboration: SMAP Observations Serving Society
The SMAP project has worked with the NASA Earth Science Division Applied Sciences Program (now known as Earth Science to Action) and the natural hazards monitoring and forecasting communities for pre- and post-launch implementation of SMAP products in their operations. In some operational applications, for which long-term data continuity is a requirement, the SMAP data are still used for assessment of current conditions, as well as research and development.
The Original Early Adopters
Prior to its launch, the SMAP mission established a program to explore and facilitate applied and operational uses of SMAP mission data products in decision-making activities for societal benefit. To help accomplish these objectives, SMAP was the first NASA mission to create a formal Applications Program and an Early Adopter (EA) program, which eventually became a requirement for all future NASA Earth Science directed satellite missions. SMAP’s EA program increases the awareness of mission products, broadens the user community, increases collaboration with potential users, improves knowledge of SMAP data product capabilities, and expedites the distribution and uses of mission products after launch.
SMAP Data in Action
Several project accomplishments have been achieved primarily through an active continuous engagement with EAs and operational agencies working towards national interests. SMAP soil moisture data have been used by the U.S. Department of Agriculture (USDA) for domestic and international crop yield applications. For example the USDA’s National Agricultural Statistics Service (NASS) conducts a weekly survey of crop progress, crop condition, and soil moisture condition for U.S. cropland. NASS surveys and publishes state-level soil moisture conditions in the NASS Crop Progress Report.
The traditional field soil moisture survey is a large-scale, labor-intensive data collection effort that relies heavily on responses from farmers, agricultural extension agents and/or other domain experts for field observations. One weakness of these observations is that they are based on subjective assessments rather than quantitative measures and can lead to spatial inconsistency based on the human responses from the respective counties. Moreover, the NASS Crop Progress Reports do not provide specific geolocation information for the assessed soil moisture conditions – which are extremely useful metadata to provide to data users. NASS implemented the use of SMAP observations in their weekly reports during the growing period (March–November). SMAP maps estimated root-zone soil moisture for the week of November 14–20, 2022, over NASS Pacific (California and Nevada) and Delta (Arkansas, Mississippi and Louisiana) regional domains—see Figure 5.
Figure 5. SMAP-based soil moisture estimates for California, Nevada, Arkansas, Mississippi, and Louisiana, used by the U.S. Department of Agriculture’s (USDA) National Agricultural Statistics Service (NASS) in their weekly report covering November 14–20, 2022. These data are available for selected states at the NASS website linked in the text. Figure Credit: NASS SMAP Radio Frequency Interference Detection and Mitigation
Although SMAP operates within the protected frequency allocation of 1400–1427 MHz, the radiometer has been impacted by radio frequency interference over the mission lifetime. Unauthorized in-band transmitters as well as out-of-band emissions from transmitters operating adjacent to the allocated spectrum have been observed in SMAP measurements since its launch. The previously launched SMOS and Aquarius radiometers provide evidence of global RFI at L-band. Consequently, SMAP was designed to incorporate a novel onboard digital detector on the back end to enable detection and filtering of RFI. The radiometer produces science data in time and frequency, enabling the use of multiple RFI detection methods in the ground processing software.
On-orbit data demonstrate that the RFI detection and filtering performs well and improves the quality of SMAP brightness temperature measurements. The algorithms are most effective at filtering RFI that is sparse in time and frequency, with minimal impact on the noise equivalent delta temperature (NEDT) – a measure of the radiometer sensitivity. Some areas of the globe remain problematic as RFI that is very high level and persistent results in high percentages of data loss due to removal of contaminated data. A global map of RFI detection rate for January 2025 shows a large contrast between Eastern and Western Hemispheres and between Northern and Southern Hemispheres – see Figure 6. Regions of isolated RFI and severe RFI correspond to populated areas. A detection rate of 100% means all pixels are flagged and removed, resulting in data loss. Analysis of spectral information reveal many sources are likely terrestrial radar systems; however, many wideband, high-level sources and low-level, non-radar sources also persist. Over areas of geopolitical conflict, the time-frequency data show interference covering the entire radiometer receiver bandwidth.
Figure 6. Percentage of pixels on a 0.25° grid for January 2025 that have been flagged for removal by the Soil Moisture Active Passive radio frequency interference detection algorithms. Figure Credit: Priscilla N. Mohammed [GSFC] The RFI challenge is further addressed through official spectrum management channels and formal reports that include the geolocated coordinates of sources, interference levels, frequency of occurrence during the observed period, and spectral information – all of which aid field agents as they work to identify potential offenders. Reports are submitted to the NASA Spectrum office and then forwarded to the country of interest through the Satellite Interference Reporting and Resolution System.
SMAP Science Data Products
The current suite of SMAP science data products is available in the Table. The principal data products are grouped in four levels designated as L1–4. The L1 products are instrument L-band brightness temperature in Kelvin and include all four Stokes parameters (i.e., horizonal and vertical polarization as well as third and fourth Stokes). Both 6:00 AM equatorial crossing (descending) and 6:00 PM equatorial crossing (ascending data) are contained in the products. The user has access to quality flags of the conditions under which measurements are available for each project. The L1B products are time-ordered and include fore and aft measurements. L1C products are on the Equal-Area Scalable Earth V2 (EASE2) grid with polar and global projections. L2 data products are geophysical retrievals (i.e., soil moisture, VOD, and binary freeze/thaw classification on a fixed Earth grid). The L2 half-orbit products are available to the public within a day of acquisition. L3 products are daily composites and include all half-orbits for that day.
The SMAP project also produces L4 data that are the result of data assimilation. The L4 products take advantage of other environmental observations, such as precipitation, air temperature and humidity, radiative fluxes at the land surface, and ancillary land use and soil texture information, to produce estimates of surface [nominally 0–5 cm (0–2 in)] and subsurface (e.g., root-zone up to a meter) soil moisture. The data assimilation system is a merger of model and measurements and hence resolves the diurnal cycle of land surface conditions. The data assimilation system also provides estimates of surface fluxes of carbon, energy, and water, such as evaporation, runoff, gross primary productivity (GPP), and respiration. The difference between GPP and respiration is the net ecosystem exchange, which is the net source/sink of the carbon cycle over land.
The SMAP suite of products also include near-real-time (NRT) brightness temperature and soil moisture products for use in operational weather forecast applications. The NRT product targets delivery to users within three hours of measurement acquisition. The NRT uses predicted SMAP antenna pointing (instead of telemetry) and model predicted ancillary data (soil temperature) in order to support operational centers that require more than three hours of data products for updating weather forecast models. To date SMAP has met its required and target (for NRT) latency requirements.
Two other data projects merge synergistically with other (colocated) satellite measurements. The SPL2SMAP_S merges SMAP L-band radio brightness measurements with C-band synthetic aperture radar (SAR) measurements from the ESA Copernicus Sentinel-1 mission. The SAR data have high resolution and allow the generation of 1 and 3 km (0.62 and 1.8 mi) merged surface soil moisture estimates. The high resolution soil moisture information, however, is only available when there is coincident SMAP and Sentinel-1 measurements. The refresh rate of this product is limited and can be as long as 12 days.
The merged SMOS–SMAP passive L-band radiometry data allows the generation of global, near daily surface soil moisture estimates, which are required to resolve fast hydrologic processes, such as gravity drainage and recharge flux. These parameters are only partially resolved with the SMAP, with a two to three day data refresh rate. This product interpolates the multi-angular SMOS data to the SMAP 40º incident angle and uses all SMAP algorithms, including correction of waterbody impact on SMAP brightness temperature, and ancillary data for geophysical inversions to soil moisture and VOD, ensuring consistency. The combined SMAP–SMOS data product may not be available daily across locations, such as Japan, parts of China, and the Middle East, where RFI affects data collection.
Table. Soil Moisture Active Passive suite of science products are available through the National Snow and Ice Data Center, one of NASA’s Distributed Active Archive Centers.
Product Type Product description Resolution (Gridding) Granule Extent SPL1BTB Geolocated, calibrated brightness temperature in time order 36 km Half Orbit SPL1CTB_E Backus-Gilbert interpolated, calibrated brightness temperature in time order (9 km) Half Orbit SPL1CTB Geolocated, calibrated brightness temperature on Equal-Area Scalable Earth V2 (EASE2) grid 36 km Half Orbit SPL1CTB_E Backus-Gilbert interpolated, calibrated brightness temperature on EASE2 grid (9 km) Half Orbit SPL2SMP Radiometer soil moisture and vegetation optical depth 36 km Half Orbit SPL2SMP_E Radiometer soil moisture and vegetation optical depth based on SPL1CTB (9 km) Half Orbit SPL2SMAP_S SMAP radiometer/Copernicus Sentinel-1 soil moisture 3 km Sentinel-1 SPL3SMP Daily global composite radiometer soil moisture and vegetation optical depth based on SPL1CTB 36 km Daily–Global SPL3SMP_E Daily global composite radiometer soil moisture and vegetation optical depth based on SPL1CTB_E (9 km) Daily–Global SPL3FTP Daily composite freeze/thaw state based on SPL1CTB 36 km Daily–Global SPL3FTP_E Daily composite freeze/thaw state based on SPL1CTB_E (9 km) Daily–Global SPL4SMAU Surface and Root Zone soil moisture 9 km 3 hours – Global SPL4CMDL Carbon Net Ecosystem Exchange 9 km Daily–Global SPL1BTB_NRT Near Real Time Geolocated, calibrated brightness temperature in time order 36 km Half Orbit SPL2SMP_NRT Near Real Time Radiometer soil moisture 36 km Half Orbit L2/L3 SMOS SM SMOS soil moisture and VOD based on SMAP algorithms (9 km) Half Orbit/Daily Global Future Directions for the SMAP Active–Passive Algorithm
Although the SMAP radar failed not long after launch, the data that were collected have been used to advance the development of the SMAP Active–Passive (AP) algorithm, which will be applied to the combined SMAP radiometer data and radar data from the NASA–Indian Space Research Organisation (ISRO) Synthetic Aperture Radar [NISAR] mission, a recently-launched L-Band Synthetic Aperture mission to produce global soil moisture at a spatial resolution of 1 km (0.62 mi) or better. The high resolution product can advance applications of SMAP data (e.g., agricultural productivity, wildfire, and landslide monitoring).
Data Continuity Beyond SMAP
A forthcoming mission meets some – but not all – of the SMAP measurement requirements and desired enhancements. The European Union’s Copernicus Program Copernicus Imaging Microwave Radiometer (CIMR) mission is a proposed multichannel microwave radiometry observatory that includes L-band and four other microwave channels sharing a large mesh reflector. The mesh reflector is similar to the one that is used on SMAP, but larger. The successful SMAP demonstration of rotating large deployable mesh antennas for Earth observations has been useful to the CIMR design.
In terms of RFI detection capability, CIMR will also use an approach that is similar to SMAP. With regard to instrument thermal noise (NEDT) and data latency, CIMR meets or comes close to the next-mission desired characteristics and equals or exceeds SMAP in most of the attributes. The native L-band resolution of CIMR is ~60 km (37 mi); however, the measurements are coincident and higher-resolution measurements in this configuration allow reconstruction of L-band radiometry at higher resolution than CIMR’s L-band. It may be possible to combine the L- and C-bands and achieve a reconstructed ~15 km (9 mi) L-band product based on the coincident and overlapping measurements. A refresh rate of one day is possible with the wide-swath characteristic of CIMR.
CIMR is currently in development; the first version, CIMR-1A, is expected to launch within this decade and the second version, CIMR-1B, in the mid 2030s. Since the Copernicus program supports operational activities (e.g., numerical weather prediction), the program includes plans for follow-on CIMR observatories so that the data record will be maintained without gaps in the future.
Conclusions
The SMAP mission was launched in 2015 and has produced over 10 years of science data. Because of its unique instrument and operating characteristics, the global low-frequency microwave radiometry with the SMAP observatory has resulted in surface soil moisture, vegetation optical depth, and freeze/thaw state estimates that outperform past and current products. The data have been widely used in the Earth system science community and also applied to natural hazards applications.
The Earth system science and application communities are actively using the decade-long, high-quality global L-band radiometry. The intensity and range of SMAP science data usage is evident in the number of peer-reviewed journal publications that contain SMAP or Soil Moisture Active Passive in their title or abstract and use SMAP data in the study (i.e., search: www.webofscience.com data-base). The authors acknowledge that many publications escape this particular query approach. Currently the bibliography includes over 1700 entries and over 20,000 citations spanning several elements of Earth system science, including hydrologic science and regional and global water cycle, oceanic and atmospheric sciences, cryosphere science, global ecology as well as microwave remote sensing technologies.
To Learn More About SMAP
A more comprehensive bibliography of studies published based on SMAP data products, a set of one-page SMAP science and applications highlights in standardized format, and SMAP project documents including assessment reports are all available online via the links provided.
Acknowledgements
The authors wish to acknowledge the contributions of the SMAP Science Team, the SMAP Algorithm Development Team, and the SMAP Project Office engineers and staff. All of these teams contribute to the ongoing SMAP science product generation and uses reported in this article.
Dara Entekhabi
Massachusetts Institute of Technology
darae@mit.edu
Simon Yueh
Jet Propulsion Laboratory/California Institute of Technology
simon.h.yueh@jpl.nasa.gov
Rajat Bindlish
NASA Goddard Space Flight Center
rajat.bindlish@nasa.gov
Mark Garcia
Jet Propulsion Laboratory/California Institute of Technology
mark.d.garcia@jpl.nasa.gov
Jared Entin
NASA Headquarters
jared.k.entin@nasa.gov
Craig Ferguson
NASA Headquarters
craig.r.ferguson@nasa.gov
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Last Updated Aug 18, 2025 Related Terms
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By NASA
The 33rd SpaceX commercial resupply services mission for NASA, scheduled to liftoff from the agency’s Kennedy Space Center in Florida in late August, is heading to the International Space Station with an important investigation for the future of bone health.
The experiment will test how microgravity affects bone-forming and bone-degrading cells and explore potential ways to prevent bone loss. This research could help protect astronauts on future long-duration missions to the Moon and Mars, while also advancing treatments for millions of people on Earth who suffer from osteoporosis.
Mesenchymal stem cells (MSCs) are derived from human bone marrow and stained with rapid red dye NASA Space’s Hidden Health Mystery
During long-duration missions, astronauts may experience a gradual reduction in bone density—typically around 1% to 2% per month—even with consistent exercise routines. While scientists understand how bones work on Earth, they aren’t sure exactly why bones weaken so quickly in microgravity.
Previous research aboard the space station revealed that microgravity changes how stem cells behave and what substances they release. Scientists now want to dig deeper into these cellular changes to better understand what causes bone loss in space and explore potential ways to prevent it.
Blocking a Potential Bone Thief
The Microgravity Associated Bone Loss-B (MABL-B) investigation focuses on special stem cells called mesenchymal stem cells, or MSCs. As these cells mature, they build new bone tissue in the body.
Scientists suspect that a protein called IL-6 might be the culprit behind bone problems in space. Data from the earlier MABL-A mission suggests that microgravity promotes the type of IL-6 signaling that enhances bone degradation. The MABL-B experiment will investigate this by testing ways to block this IL-6 signaling pathway.
The experiment will grow mesenchymal stem cells alongside other bone cells in special containers designed for space research. Cells will be cultured for 19 days aboard the space station, with crew members periodically collecting samples for analysis back on Earth.
How this benefits space exploration
The research could lead to targeted treatments that protect astronauts from bone loss during long-duration missions to the Moon, Mars, and beyond. As crews venture farther from Earth, bone health becomes increasingly critical since medical evacuation or emergency return to Earth won’t be possible during Mars missions.
How this benefits humanity
The findings could provide new insights into age-related bone loss that affects millions of people on Earth. Understanding how the IL-6 protein affects bone health may lead to new treatments for osteoporosis and other bone conditions that come with aging.
Related Resources
Microgravity Associated Bone Loss-B (MABL-B) Microgravity Associated Bone Loss-A (MABL-A) Microgravity Expanded Stem Cells About BPS
NASA’s Biological and Physical Sciences Division pioneers scientific discovery and enables exploration by using space environments to conduct investigations not possible on Earth. Studying biological and physical phenomenon under extreme conditions allows researchers to advance the fundamental scientific knowledge required to go farther and stay longer in space, while also benefitting life on Earth.
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Roscosmos cosmonaut Kirill Peskov, left, NASA astronauts Nichole Ayers and Anne McClain, and JAXA (Japan Aerospace Exploration Agency) astronaut Takuya Onishi are seen inside the SpaceX Dragon spacecraft on the company’s recovery ship shortly after splashdown in the Pacific Ocean off the coast of San Diego, California, on Aug. 9, 2025.Credit: NASA/Keegan Barber After spending almost five months in space, NASA’s SpaceX Crew-10 astronauts will discuss their science mission aboard the International Space Station during a news conference at 4:15 p.m. EDT, Wednesday, Aug. 20, from the agency’s Johnson Space Center in Houston.
NASA astronauts Anne McClain and Nichole Ayers, and JAXA (Japan Aerospace Exploration Agency) astronaut Takuya Onishi will answer questions about their mission. The crew returned to Earth on Aug. 9.
Live coverage of the news conference will stream on the agency’s YouTube channel. Learn how to watch NASA content through a variety of additional platforms, including social media.
This event is open to media to attend in person or virtually. For in-person, media must contact the NASA Johnson newsroom no later than 12 p.m., Tuesday, Aug. 19, at: jsccommu@mail.nasa.gov or 281-483-5111. Media participating by phone must dial into the news conference no later than 10 minutes prior to the start of the event to ask questions. Questions also may be submitted on social media using #AskNASA. A copy of NASA’s media accreditation policy is available on the agency’s website.
The crew spent 146 days aboard the orbiting laboratory, traveling nearly 62,795,205 million miles and completing 2,368 orbits around Earth. While living and working aboard the station, the crew completed hundreds of science experiments and technology demonstrations. The latest NASA space station news, images, and features are available on Instagram, Facebook, and X.
NASA’s Commercial Crew Program has delivered on its goal of safe, reliable, and cost-effective transportation to and from the International Space Station from the United States through a partnership with American private industry. This partnership is opening access to low Earth orbit and the International Space Station to more people, more science, and more commercial opportunities. For almost 25 years, people have continuously lived and worked aboard the space station, advancing scientific knowledge and demonstrating new technologies that enable us to prepare for human exploration of the Moon as we prepare for Mars.
Learn more about NASA’s Commercial Crew Program at:
https://www.nasa.gov/commercialcrew
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Joshua Finch
Headquarters, Washington
202-358-1100
joshua.a.finch@nasa.gov
Courtney Beasley
Johnson Space Center, Houston
281-483-5111
courtney.m.beasley@nasa.gov
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Last Updated Aug 14, 2025 EditorJessica TaveauLocationNASA Headquarters Related Terms
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By Space Force
The US Space Force, in partnership with the Air Force Rapid Capabilities Office and SpaceX, is making final preparations to launch the eighth mission of the X-37B Orbital Test Vehicle.
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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 19 min read
A Tapestry of Tales: 10th Anniversary Reflections from NASA’s OCO-2 Mission
When woven together, the tapestry of experiences of staff and scientists provide the complete picture of OCO-2.
Breathe in… Breathe out.
This simple rhythm sets the foundation of life on Earth – and it’s a pattern that a NASA satellite has been watching from space for over a decade.
On July 2, 2024, NASA’s Orbiting Carbon Observatory-2 (OCO-2) celebrated 10 years since its launch. Built by NASA/Jet Propulsion Laboratory (NASA/JPL), OCO-2 is now viewed as the gold standard for carbon dioxide (CO2) measurements from space and has quietly become a powerful driver of technological, ecological and even economic progress – including providing unexpected insights into plant health, crop-yield forecasting, drought early warning systems, and forest and rangeland management.
While the mission can point to many scientific achievements – some of which will be highlighted in the pages that follow – these accomplishments have occurred in the context of a larger human story. Scientists from around the world have come together to bring the important data from this satellite to the broader community, making OCO-2 the success that it is today.
This article provides readers an introduction to several transformative characters in this carbon story. The text peers behind the scenes to reveal the circuitous path that scientists and engineers must navigate to take a brilliant scientific concept and turn it into flight hardware that can be launched into space to make beneficial observations. The article depicts milestones that mark the mission’s successes, but also the failures, dead ends, long nights, and discouragements that make up the complexity of any science story.
2003: The First OCO Science Team Meeting
Measuring CO2 from space: Great idea but can it really be done?
When the idea for OCO was first proposed, it wasn’t universally embraced. At the time, more than a few experts scoffed at the idea that CO2 could be measured from space. Unlike nitrogen and oxygen, which are the dominant components of Earth’s atmosphere, CO2 is a trace gas, often no more than a few hundred parts per million. Miniscule, elusive, and nomadic, these measurements, though challenging, are crucial because of the important role CO2 plays in global climate.
In April 2003, a handful of hopeful scientists gathered at the California Institute for Technology (Caltech) for the first OCO Science Team meeting. To mark the occasion, they took a break during the meetings and lined up for a group photo – see Photo 1. Upon returning to work, they took up the arduous task of determining how to measure CO2 from space with a satellite and instrument hardware that simply did not exist.
OCO-2 was developed as part of NASA’s Earth System Science Pathfinder program, which supports small, low-cost missions that can still provide tremendous value for high-impact goals. The satellite carries a high-resolution spectrometer that collects data in three, narrow spectral bands. These spectral bands follow a divide and conquer strategy – two measure the clear “fingerprint” that CO2 leaves when it absorbs sunlight, and one takes the same measurement for oxygen (O2). The satellite is able to estimate CO2 concentrations by comparing the CO2 and O2 measurements.
Photo 1. A photo of participants during the original OCO Science Team meeting in 2003 at the California Institute of Technology. Photo credit: NASA/Jet Propulsion Laboratory OCO-2 2014: A Night at Vandenberg Air Force Base – To Launch or Not to Launch
A Mother and daughter await the midnight launch.
On a warm July evening in 2014, Vivienne Payne [JPL—current OCO-2 Project Scientist] would normally have tucked her four-year-old daughter into bed. But this night was special. They were lined up in a crowd waiting for a bus to take them to Vandenberg Air Force Base (now Space Force Base) in California. The group huddled in the chill night air awaiting the launch of the OCO satellite into the cosmos.
Shortly after midnight, hundreds of guests spread blankets across the gravelly ground to make their wait more comfortable. The air was charged with excitement. The participants waited quietly, murmuring to one another while the soft slosh of the Pacific Ocean offered a steady pendulum counting down to the impending launch. Like most people there that night, Vivienne felt upbeat and excited, but she also understood the gravity of the moment – a lot was riding on this launch.
While Vivienne had not been part of OCO since inception – having joined the project in 2012 – she knew OCO’s story. The first launch in 2009 ended in failure – when a faulty launch vehicle doomed the first OCO to a watery grave just moments after launch. In the aftermath, the OCO community were left in limbo, unsure if the project would survive. All was not lost. The Japan Aerospace Exploration Agency (JAXA) had successfully launched the Greenhouse-gas Observing satellite (GOSAT or IBUKI, Japanese for “breath”) that same year. This launch gave the OCO team an opportunity to test and refine their methods and algorithms using data from GOSAT.
As the gravel poked through the thick flannel blankets, Vivienne shifted uncomfortably waiting for the interminable countdown to reach its conclusion – and then everything stopped. A technical issue was detected, triggering a command to abort the launch.
Vivienne tried to explain to her disappointed daughter that this was simply how things went with space work. Sometimes you put in 1000 work-years of labor, get up in the middle of the night, and sit on uneven ground just to have everything stopped, unceremoniously.
Fortunately, the problem was quickly resolved, and the launch was rescheduled for the very next night. The participants returned to the staging site – rinse and repeat. This time Vivienne’s daughter was decidedly more sluggish. At 3:00 AM PDT, OCO-2 launched flawlessly into space. Unfortunately, a layer of fog obscured the spectators’ view. While it could not be seen, the resounding boom of the rocket taking off could be heard for miles.
For Vivienne, the sonic boom shocked the ears and rumbled through the bodies of the assembled crowd, who erupted in cheers. Having invested a lot of her time in the OCO project during the past two years, she was thrilled to see a successful launch.
As they returned to their hotel, Vivienne’s daughter remained unimpressed. “Mummy, let’s not do that again,” she said as she splayed out on the hotel bed and soon fell fast asleep.
2014: OCO-2 Joins A Larger Earth Observing Story
Leading to surprising new insights about how we see plants – and fires.
When OCO-2 launched in 2014, it joined a tightly coordinated group of Earth-observing satellites known as the Afternoon Constellation (or the “A-Train”) – see Figure 1. Flying in formation, the satellites could combine their observations to unlock more than any one mission could reveal on its own. Around the same time, scientists discovered that OCO-2 could do more than measure CO2 – it could also detect signs of plant health.
Figure 1. As of January 2024, the international Afternoon Constellation (“A-Train”) has two missions remaining: OCO-2 and GCOM-W. While Aqua and Aura continue to collect science data, the satellites have both slowly drifted out of the constellation – and will soon be decommissioned. CALIPSO ended its scientific mission on August 1, 2023. CloudSat radar operations ceased on December 20, 2023. Figure credit: NASA This discovery opened the possibilities for many different people, including Madeleine Festin, a former wildland firefighter in Montana, to work with OCO-2 data through an internship sponsored by the DEVELOP program, under the Earth Action element (formerly known as Applied Sciences) of NASA’s Earth Science Division.
When she was on the ground battling fires, Madeleine faced the harsh reality that fire prediction is notoriously difficult. In the field, she might be surrounded by smoke with just 20 ft (6 m) of visibility and red flames tearing through dry brush. Through her internship, she’s continued to tackle fires – just from a very different vantage point.
OCO-2 can detect the faint glow given off by plants during photosynthesis. This glow, called solar-induced fluorescence (SIF), offers a fast, sensitive indicator of plant health – see Figure 2. While other satellite-based tools, such as soil moisture or vegetation indices often detect stress only after damage has already occurred, SIF values drop the moment photosynthesis slows down – even if the plant still looks green. These data open the door to new applications: monitoring crop performance, identifying flood-damaged areas, and tracking drought before it sparks wildfires. That’s exactly how Madeleine is now using the data.
Madeleine’s team, a collaboration between OCO-2 scientists and the U.S. Forest Service, is working to update fire-risk models – some of which were developed in the 1980s – by incorporating SIF data.
“It’s fulfilling to know that you’re helping people,” Madeleine says. “And it’s nice to see science and firefighting work align.”
What makes the data even more powerful is OCO-2’s synergy with its A-Train counterpart, the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’S Aqua platform. MODIS contributes land-cover information that, when paired with OCO-2’s SIF measurements, creates a detailed, global dataset of plant photosynthesis far beyond what either satellite could produce on its own. This example is a perfect synergistic pairing of measurements the A-Train has made possible. This information gives Madeleine and her team a better foundation for improving fire prediction tools.
“When firefighting, I used to hear about all these fire indices and metrics, and never knew what they meant,” Madeleine says. “Now, I’m learning the science behind it. And it’s interesting to think about how to get that information to firefighters on the ground, without overburdening them. What do they really need to know, and how can we deliver it in a way that helps?”
Figure 2. OCO-2 can measure plant health and photosynthesis from space. Puente Hills in eastern Los Angeles County, CA was once one of the largest landfills in the United States. The landfill has since been closed and its surface replanted to resemble a natural hill rising above the surrounding densely populated neighborhoods. These two images show how solar induced fluorescence (SIF), or “plant glow,” measured from OCO-2 and OCO-3 can be used to study urban greenery. The satellite image of the landfill and surrounding area [left] is followed by the SIF data overlay [right]. It is possible to compare the photosynthetic activity in the reclaimed landfill to nearby green spaces, as well as the plant health in the surrounding neighborhoods. Figure credit: NASA/Jet Propulsion Laboratory OCO-2, OCO-3 2016: Trekking to the Desert to Calibrate OCO-2
A technologist tramps around in the desert for instrument calibration.
Carol Bruegge [OCO-2—Technologist] had been to the Nevada desert so many times that she knew the way by heart. After skirting the Sequoia Forest and stopping for the night just past the Nevada border, she led a caravan of scientists along Highway 6 to mile marker 100, turning right onto a dirt road between two fence posts. Traveling 10 mi (16.5 km) down the road, a cloud of dust raised up from the car tires before the vehicle came to a stop at their destination – a patch of spindly instruments hammered into the barren desert floor. A big plaque marked the spot with the NASA logo and the words, “Satellite Test Site.” Standing under vast blue sky, Carol felt like she’d come home. Over the past few years, Carol had grown accustomed to leading these summer expeditions to Railroad Valley, NV. Often the team from JPL is joined by guests from Japan and other international colleagues representing various satellite missions – see Photo 2.
Photo 2. Group photo at Railroad Valley, NV during a summer field campaign. Carol Bruegge [OCO-2—Technologist, fifth from left] joins JPL members and guests from Japan working on the Greenhouse-gas Observing satellite. The group included [left to right] Hirokazu Yamamoto, Atsushi Yasuda, Hideaki Nakajima, Kei Shiomi, Thomas Pongetti, Bruegge, Dejian Fu, Junko Fukuchi, Makoto Saito, and Rio Kajiura. Photo credit: Tom Pongetti Carol knew that a successful field campaign required that they protect the instruments from the thick corrosive salt on the ground. Then the work could begin. The team hiked through the desert, collecting data that would ensure that OCO-2 could continue to provide high-quality data. As they hiked, the team carried hand-held spectrometers and measured the reflection of sunlight off Earth’s surface – timed precisely to match the moment the satellite passes overhead. By comparing the satellite’s readings with the ground-based measurements, the team can check the accuracy of the satellite readings. Reflection is one ingredient used in calculating the concentration of CO2 in the overlying air.
This remote location in Nevada wasn’t chosen by accident. In this part of the desert, the ground is perfectly flat, free of plants, and surrounded by ground littered with salt. This smooth, bare surface means no bumps and textures could disrupt the signal. For satellite calibration, it doesn’t get better than this.
2018: A Contentious Meeting in Noordwijk, Netherlands Sparks A Revolution
Could OCO-2 data be used to construct a nation-by-nation CO2 budget?
David Crisp [JPL emeritus—original OCO Principal Investigator and former OCO Science Team Leader] was tired. He didn’t know if it was jet lag or a reflection of the 16- to 18-hour workdays that had persisted for weeks. This particular week had started with a 10-hour flight from Los Angeles to the Netherlands. Now, he was standing in front of carbon scientists who had gathered from around the world.
“We need to put together a team that will be brave enough to make a CO2 budget, nation-by-nation,” David said.
His statement was met with thoughtful silence. Neither the data nor the models were ready. The consensus in the room was that the proposed venture may not work. David was magnanimous toward his critics, but he persisted with his idea.
Despite the rocky start, David met with representatives in charge of creating national emission inventories. He could see exasperation on their faces – running ragged, short-staffed, and trying to tally up every single barrel of oil and bushel of coal burned within their country’s boundaries. Even more challenging was tallying other tasks, such as deforestation and agricultural practices. David firmly believed that if OCO-2 could provide independent estimates from space as promised, it would provide the on-the-ground “carbon accountants” a reliable comparison – see Figure 3.
“We might have a satellite that can help,” Dave told them.
Although David has since retired, his perseverance is now bearing fruit. What began as a hypothetical solution is now much closer to reality. OCO-2’s high-precision measurements can now detect CO2 linked not just to countries, but large cities, industrial zones, and even individual power plants – all while researchers continue perfecting efforts to identify contributions from specific city sectors. OCO-2 provides a valuable, independent reference that nations can use to track the progress of their emission inventories. Researchers have created an entire OCO-2-sourced database of CO2 estimates by country, available through the U.S. Greenhouse Gas Center.
Figure 3. A map of the net emissions and removals of carbon dioxide (CO2) for 2015–2020 using estimates informed by OCO-2. Green depressions represent countries that remove more CO2 than emitted. Tan or red ridges represent countries with higher CO2 emissions than removed. Figure credit: NASA Science Data Visualization Studio 2019: Another OCO Takes flight – This Time to The International Space Station
Using “spare parts” to get more details about plant health and the carbon cycle.
After completing OCO-2, enough spare parts remained to construct a sister mission — OCO-3, which launched in 2019 to continue the work of measuring CO2 in the atmosphere from the International Space Station (ISS). The satellite’s unique orbit gives it a new vantage point. While OCO-2 continues to orbit Earth in a near-polar path, OCO-3 travels aboard the ISS in a lower, shifting orbit that allows it to study different areas of Earth’s surface at different times of day. OCO-3 also features a special scanning mode, called the snapshot area mapping (SAM) that lets scientists zoom in on areas of interest (e.g., cities or volcanoes) to study carbon emissions and vegetation in greater detail. Together, OCO-2 and OCO-3 provide complementary perspectives on Earth’s carbon cycle and plant health at space and time resolutions that have not been possible from space before.
2021: LA During a Pandemic Is a Far Cry from Finland
A data scientist foregoes saunas and berry-picking to make the dream of OCO-2 a reality.
Otto Lamminpää [JPL—Data Scientist] opened the picture his sister had texted him. His family looked back with wide smiles, holding buckets overflowing with scarlet berries and framed by the velvety firs of Finland. It had been almost two years since he’d seen them in person. He’d moved to Los Angeles to work at JPL on the OCO-2 and OCO-3 mission just as the COVID-19 pandemic engulfed the planet – see Photo 3.
Photo 3. Otto Lamminpää and Amy Braveman [both from JPL] in Finland. Photo credit: Otto Lamminpää Otto had never gone a week without seeing his family or skipped a berry-hunting party in the forests of his native Finland. With the forced distance, he placed himself in his home forests in his mind. He used this memory to marvel at the capacity of the vast forests to “breathe in” CO2 and convert it into trunks, branches, and roots through photosynthesis. With the COVID-19-imposed travel restrictions, Otto wasn’t sure how long he’d have to wait to go back home.
But whenever that homecoming occurred, Otto knew that a piece of OCO-2 would be waiting for him. North of the Arctic Circle in Sodankylä, a cluster of Earth instruments nestled in a snowy meadow include a field station that is part of the Total Carbon Column Observing Network (TCCON) of Fourier Transform Spectrometers (FTS). These stations act as OCO-2 and OCO-3’s “ground crew.” As the satellites orbit Earth, the FTS simultaneously measures direct solar spectra in the near-infrared spectral region, which allows for retrieval of column-averaged CO2 concentrations, as well as other key atmospheric constituents, over the snowy meadow. Back in the lab, Otto, along with other OCO-2 and OCO-3 scientists, compare the data collected at the field station to the satellite data. This feature was detailed in The Earth Observer article, titled “Integrating Carbon from the Ground Up: TCCON Turns Ten,” was published July–August 2014, Volume 26 issue 4, pp. 13–17).
Figure 4. Global map of the ground stations, also known as the Total Carbon Column Observing Network (TCCON). The red dots mark the active ground observation stations to validate OCO-2 and OCO-3 data. Figure credit: NASA-JPL/OCO-2 The station in Finland is one of about 30 similar TCCON sites scattered across the world, located in a variety of settings, from isolated tropical islands to the Pacific rim of Asia – see Figure 4. The stations in the far north play an especially valuable role since satellites often struggle to accurately measure CO2 over snow-covered ground. Therefore, reliable measurements from the ground stations become crucial to adjust and improve the satellite data.
Validation efforts such as the one described here are crucial to satellite observations. Comparisons between OCO-2 and TCCON show agreement is good, with a less than 1 ppm difference. It’s an impressive level of accuracy for a satellite orbiting more than 435 mi (700 km) away in polar orbit. The “ground truth” data collected at these field sites help to ensure that the satellite is accurately measuring “Earth’s breathing.”
For Otto, not just his family, but OCO-2 and OCO-3 itself was calling him home. As the pandemic began to ease, he returned to Finland to pick berries, jump in the sauna every night, and follow it up with snow angels. The homecoming was also coordinated with a trip past the Arctic Circle to the TCCON field station. The mission was part of him. Wherever he was, OCO-2 and OCO-3 would be there, too.
2023: The Annual Science Team Meeting Continues
Tracking changes in soil moisture during a colorful fall day.
Saswati Das [JPL—Postdoctoral Fellow] had missed the magnificent display of fall colors in deciduous forests of the East Coast of the United States. She’d seen nothing of the sort since moving to Los Angeles in 2022 to work on OCO-2. Before that, she’d been working on her Ph.D. at the Virginia Polytechnic Institute and State University (Virginia Tech), where the surrounding mountain peaks, meadows, and forests burned and sparked with crimson and gold in the autumn – see Photo 4. Now she was in another mountain town, Boulder, CO, to attend the OCO science team meeting. The aspens glittered like golden lanterns as her gang carpooled up the Flatiron Range to the science institute at Table Mesa.
Photo 4. Saswati Das takes a break from her Ph.D studies at nearby Virginia Tech (located in Blacksburg, VA) to enjoy the famous fall colors in the mountains of West Virginia. Photo credit: Saswati Das The research presented that week spanned a variety of topics. OCO-2 was being used to develop early drought forecasts. Because of its ability to detect the SIF “glow” that results from plant photosynthesis, OCO-2 can hint at flash droughts as early as three months before environmental decay unfold. By pairing OCO-2 data from other satellites, such as soil moisture data from NASA’s Soil Moisture Active Passive (SMAP) mission, scientists have opened a new window into drought forecasts and how water supply affects plant growth.
Surprises about our planet have also emerged. The tropical rainforests, long nicknamed the “lungs” of our planet, don’t always inhale and store carbon. At times, this region can exhale CO2, such as during the 2015–2016 El Niño. That period saw large tropical forests temporarily transform into net carbon sources – see Figure 5. The driver for this shift varied by region. The Amazon rainforest was driven by drought. Central Africa was driven by unusually high temperatures. Indonesia was driven by widespread fires.
Figure 5. The 2015–2016 El Niño increased the net carbon dioxide released by Earth’s tropical regions into the atmosphere. Figure credit: NASA-JPL/Caltech Data from OCO-2 and OCO-3 have also been used to study emissions from both cities and large power plants. This approach offers a new way to track changing emissions over time – without needing to continuously measure them on the ground. In addition, scientists are combining the satellite data with wind models and urban maps to trace CO2 to its sources (e.g., factories, ships, and roadways), helping to disentangle emissions from overlapping city sectors. These methods have been used to isolate industrial emissions in places, such as Europe, China, as well as over cities, such as Los Angeles, Paris, and Seoul. It has also revealed pandemic-era drops in traffic-related CO2 and increases in CO2 tied to shipping backlogs at the port. Two representatives from the World Bank shared how they used data from OCO-2 to demonstrate that building subway systems in cities can lower emissions. The goal is to eventually use these tools to evaluate local strategies (e.g., bike lanes and public transit) to reduce local carbon footprints.
When massive wildfires blazed through Australian forests and bushland in 2019, researchers used OCO-2 data to study the unfolding crisis. OCO-2 captured the increase in atmospheric CO2, and scientists used this data to refine estimates of how these events contribute to the global carbon budget.
As her mind wandered from the rich research she’d been immersed in for the past hour, Saswati spied Otto Lamminpää across the aisle in the wood-paneled auditorium. She thought back to the forests she loved on the East Coast, and the forests in Finland where Otto had grown up. OCO-2 was telling a story about the role that forests play in absorbing carbon and how this has changed over time.
2025 and Beyond
The Tapestry Continues to Expand…
In many ways, OCO-2 has had a long and unexpected journey. So has Hannah Murphy, another DEVELOP intern who will be starting a Master’s degree at Hunter College in New York in Fall 2025. She’s studied art and worked as a set designer in Los Angeles. She never pictured herself working with satellite data, but then she saw how visual it could be. The glowing, evocative images of Earth from space spoke to her artistic heart.
Now, Hannah works on SIF data as a 2025 NASA DEVELOP intern with the OCO-2 team, developing tools for wildfire risks. This project in particular hits close to home for Hannah, because she lived through the wildfires that tore through Los Angeles in January 2025. Although she remained safe, she knew several people who lost their homes, and the air was unsafe to breathe for weeks.
Just a few short months later, Hannah began studying the data from OCO-2. She is now part of the new generation of researchers that will take the mission’s remote sensing data and pave the way for implementing the findings to benefit society. Hannah understands, on a personal level, how closely our lives are linked to Earth systems that satellites, such as OCO-2 and OCO-3, study from space.
OCO-2 (and OCO-3) are built to study CO2 and plant health, but its impact goes deeper to the connections that tie our atmosphere, ecosystems, and lives together. That work continues to the new generation of scientists – one breath at a time.
Mejs Hasan
NASA/Jet Propulsion Laboratory
mejs.hasan@jpl.nasa.gov
Alan Ward
NASA’s Goddard Space Flight Center/Global Science & Technology Inc.
alan.b.ward@nasa.gov
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