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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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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 12 min read
Summary of the 54th U.S.–Japan ASTER Science Team Meeting
Introduction
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Science Team (ST) organized a three-day workshop that took place June 9–11, 2025, at the Japan Space System’s (JSS) offices in Tokyo, Japan. About 25 people from Japan and the United States participated during the in-person meeting – see Photo 1.
U.S. participants included representatives of NASA/Jet Propulsion Laboratory (JPL); two universities – University of Arizona (UA) and University of Pittsburgh (UPitt); and Grace Consulting. Japanese participants represented JSS, the Geologic Survey of Japan (GSJ), National Institute of Advanced Industrial Science and Technology (AIST), National Institute for Environmental Studies (NIES), and the Remote Sensing Technology Center of Japan (RESTEC). Participants from Ibaraki University (IU), Nagoya University (NU), University of Tokyo (UT), and University of Tsukuba (Uts) also joined.
Photo 1. Several attendees sit for a photo at the 54th ASTER Science Team meeting at the Japan Space System’s offices in Tokyo, Japan. Photo credit: Osamau Kashimura The main objectives of the 54th ASTER STM were to:
discuss impacts of the proposed NASA budget reductions for Fiscal Year (FY) 2026; respond to plans for future impacts on ASTER from possible power reductions on the Terra platform; receive updates on data acquisition status, data calibration and validation (cal/val) activities, data distribution plans, and applications using ASTER observations; and discuss the end-of-mission plans for Terra and ASTER and archive documentation requirements. The remainder of this article summarizes the highlights from the meeting, which includes an overview of the opening plenary session and summaries of the four working group sessions. A brief review of the closing plenary, which included summary reports from the chairpersons of all working groups, rounds out the report, followed by some overall concluding thoughts.
Opening Plenary Session
Yasushi Yamaguchi [NU—Japan ASTER ST Lead] and Michael “Mike” Abrams [JPL—U.S. ASTER ST Lead] welcomed participants and reviewed the agenda for the opening plenary and the schedule for the working group sessions.
Abrams presented highlights of science results based on ASTER data. He also discussed some issues that Woody Turner [NASA Headquarters—ASTER Program Scientist] had raised, including NASA’s response to the President’s proposed fiscal year (FY) 26 budget and the status of FY25 funding. Abrams reported that Terra passivation is currently scheduled for February 2027 and described Terra’s power status. [UPDATE: If the President’s proposed FY26 budget goes into effect without modification by Congress, the three Flagship missions will enter accelerated Phase F (closeout); Terra passivation would start in November 2025 and be complete by March 2026.]
Abrams reviewed the status of the Terra spacecraft, showing slides provided by Jason Hendrickson [GSFC]. The Flight Operations Team staffing remains constant. Science data capture for ASTER remains above 99%. The impact of the shunt failure on November 28, 2024 required the safe halting of the instrument. Visible-near-infrared (VNIR) observations resumed in mid-January, and thermal infrared (TIR) observations resumed in mid-May. Collision avoidance events continue to be part of normal operations.
Hitomi Inada [JSS] provided a status report on the ASTER instrument. Many of the monitored components (i.e., VNIR pointing motor) are beyond their original useful life in orbit, but the aging hardware shows no signs of wearing out or a decrease in performance. She showed data that indicated that the temperature and current telemetry trends remain stable.
Abrams presented ASTER product distribution statistics provided by Cole Krehbiel [Land Processes Distributed Active Archiver Center (LP DAAC]). The ASTER Digital Elevation Model continues to be the most ordered product among all users of ASTER data. As defined by the ST at the last meeting, most ASTER data products [e.g., Version 4 (V4) products] are being created and placed in a searchable/orderable archive that can be accessed through NASA’s Earthdata tool. Abrams reported that the LP DAAC started producing these files in January 2025 and will be finished before August 2026.
Koki Iwao [GSJ] presented AIST’s product distribution statistics. Over 4.7 million scenes have been acquired and processed to Level 1A (L1A) since June 10, 2025. AIST continues to distribute ASTER’s pseudo-natural color scenes in keyhole mark-up language (KML – a file format used to display geographic data) and scene-based Digital Elevation Models. The largest number of users of Japanese products are from the United States.
Tetsushi Tachikawa [JSS] summarized the status of ASTER observations since the beginning of the mission. He reported that all of the global observation programs are functioning normally, acquiring data as planned. Updates to the observation programs will be considered by this week’s working groups. Tachikawa also added that the change of the orbit repeat – after Terra’s October 2022 exit from the Morning Constellation – has been accommodated in the ASTER scheduler.
Abrams presented a report on behalf of Simon Hook [JPL], who was unable to attend the meeting. Hook’s information provides a status update for the multispectral TIR instrument on NASA’s ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) mission. Abrams also spoke about NASA’s future Surface Biology and Geology (SBG) mission, which is part of the planned Earth System Observatory.
Applications Working Group
The applications session provided a sampling of how ASTER data are used. A few examples are highlighted below. The second half of the session was devoted to a discussion of end-of-mission documentation requirements. This included a review of the NASA guiding document and sharing of existing documents.
Michael Ramsey [UPitt] presented work on forecasting volcanic activity with the ASTER long-term archive. His team developed a statistical detection code to extract accurate temperature anomalies for five test volcanoes over 25 years. They used these results to train a deep learning approach for anomaly detection in future TIR data. The method showed 73% success for Piton del la Fournaise volcano, Réunion island, and near 100% success for Sheveluch volcano, Kamchatka Krai, Russia.
Miyuki Muto [IU] reported on waste volume changes in 15 open landfills in developing countries using more than 20 years of ASTER time-series digital surface models – see Figure 1. The method was found to be consistent with reports using synthetic aperture radar (SAR) data, which dates to 2016. Thus, ASTER can provide a longer time series for future optical or radar studies.
Figure 1. Time variation in the relative volume of waste for landfills, obtained from ASTER time-series digital surface model data for the four Indian sites – Ghazipur, Bhalswa, Okhla, and Deonar. Figure credit: Figure taken from Muto and Tonooka (2025), Sensors Mike Abrams presented the 25-year history of ASTER data applied to geologic mapping and mineral exploration. He explained how the first published papers appeared a few years after launch and validated the unique mineralogical information contained in the ASTER data. Over the following 20 years, several reports from mineral exploration companies announced the discovery of gold, chromite, and lithium deposits, which were found largely based on analysis of ASTER data.
Calibration/Validation Working Group
The Calibration/Validation (cal/val) working group is responsible for monitoring the radiometric and geometric performance of ASTER’s VNIR and TIR instruments. Three different cal/val techniques are used including: analysis of onboard calibration lamps, comparison with onboard blackbodies, and measurements of pseudo-invariant ground targets during field campaigns. The L2 software algorithms are being updated for the final, archival processing which is anticipated to be completed in May 2026.
Bjorn Eng [JPL] reported that the newest version of the L2 algorithm for ASTER VNIR and TIR cal/val was delivered to the LPDAAC for ingest and testing. Eng explained how the new software includes Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) data, which allows users to create atmospheric profiles for temperature, pressure, water vapor, and ozone. MERRA-2 is an improvement – both spatially and temporally – over the National Centers for Environmental Prediction’s Global Data Assimilation System that is used in the original MERRA. The new L2 production algorithms were validated, and the LP DAAC began incorporating the algorithms into the static archive in January 2025.
Mike Abrams presented on behalf of Cole Krehbiel [LP DAAC] and reported on the assessment of geometric performance of the L1 processing software, which was updated to the new Landsat ground control point library. He also presented an improved global digital elevation model. The ASTER final processing campaign uses the improved control point library.
Satoru Yamamoto [GSJ] presented updates to the calibration trends of the onboard VNIR lamps. Two onboard calibrations were performed on September 20, 2024 and November 8, 2024. Several analyses of the calibration lamps showed no significant change in the data trends – see Figure 2. The signal-to-noise ratios are still greater than the requirement of 140.
Figure 2. Onboard lamp calibration data for Bands 1, 2, and 3. The lamp data show no significant change in the three bands after updating the calibration. Figure credit: Satoru Yamamoto Soushi Kato [RESTEC] presented results from his September 2024 field campaign in Nevada and Utah. The campaign was marked by clear weather during ASTER’s day and night overpasses. Kato compared his in situ TIR measurements with the standard ASTER temperature products from the LP DAAC. The agreement for the five AESTER TIR bands was within ± 1.5 K.
Hideyuki Tonooka [IU] presented the results of his TIR field calibration campaigns at the same time and location as those conducted by Kato (described in previous presentation summary). Additionally, he reported that several calibration campaigns conducted at Lake Kasumigaura, Japan were cancelled due to cloudy weather, which led to the suspension of ASTER data acquisition. Tonooka compared his in situ TIR measurements with the standard ASTER temperature products from the LP DAAC. The agreement for the five ASTER TIR bands was within ± 1.3 K, except for band 10 at the Utah site where the discrepancy was -2.3 K.
Temperature–Emissivity Working Group
This group focuses on ASTER’s kinetic temperature and emissivity products, as well as application of these products and review of the nighttime TIR global mapping program status.
Mike Abrams presented his analyses of the ASTER Level-2 Surface Kinetic Temperature Product (AST_08) for a nighttime scene acquired over Lake Tahoe, CA. He compared the on-demand MERRA-2 product from NASA’s Global Modeling and Assimilation Office with the archive-produced product. The comparison showed that the two products were identical, pixel-by-pixel. Abrams conducted a second analysis to compare the archived MERRA_2 AST_08 product with the on-demand Moderate Resolution Imaging Spectroradiometer (MODIS) AST-08 product to assess the difference in temperature due to improved MERRA-2 atmospheric parameters. The MERRA-2 product had lower temperature values for higher elevations and higher values for lower elevations with more column water vapor – see Figure 3. This result is physically correct and validates the improvement using MERRA-2 atmospheric data.
Figure 3. Colorized difference by temperature, in Kelvin, between the product using MERRA-2 and MODIS atmospheric values: blue -1.0 to -0.6; green -0.5 to -0.1; red 0.0; and yellow 0.1 to 0.5. Figure credit: Michael Abrams Hideyuki Tonooka discussed the status of installation of the JPL radiometer at Lake Kasumigaura. The plan is to mount the radiometer on an existing observation in the middle of the lake. The radiometer will be operated jointly by JPL and IU. The installation is planned to start in the Summer 2025.
Tetsuchi Tachikawa reviewed the status of the current Thermal Global Mapping acquisition program to acquire cloud-free TIR nighttime images over most of the Earth’s land surface. He explained that the program is refreshed every year, with most recent refresh beginning May 2025.
Operations and Mission Planning Working Group
The Operations and Mission Planning Working Group oversees and reviews the acquisition programs executed by the ASTER scheduler. Because ASTER data acquisitions have to be scheduled every day to accommodate ASTER’s average 8% duty cycle, ST members developed an automatic program to select 600–700 daily scenes from the possible 3000 plus images uploaded in the request archive.
Tachikawa reviewed the status of acquisition scheduling. Urgent observations receive the highest priority and can be scheduled close to acquisition time. Approximately 70 scenes are programmed per month – with over 95% acquisition success. By contrast, global mapping data acquisitions receive the lowest priority and are used to fill in the scenes for the daily quota. He explained that the goal of the ASTER is to have the instrument acquire at least one cloud-free image for every place on Earth. Due to persistent cloud cover, success is typically ~85% after several years, at which time the program is restarted. Tachikawa next gave short updates on three other acquisition programs that focus on islands, volcanoes, glaciers, and cloudy areas, respectively. The global volcano image acquisition program will continue with no change to the observation parameters. Acquisition of images of islands and over cloudy areas will also continue in current form. The global glacier acquisition program will be modified to change the VNIR gain settings to optimize images over snow and ice.
Tachikawa also discussed the effect of the ASTER shutdown in November 2024 and cessation of all ASTER data acquisitions. VNIR-only acquisitions were resumed in January 2025, and TIR acquisitions resumed in May 2025, with full operations and acquisitions of data from both VNIR and TIR instruments.
Closing Plenary Session
Each chairperson summarized the presentations, discussions, and recommendations that occurred during their respective working group session. The overall consensus maintained that the ASTER instrument is operating normally again – with no indications of any component failures. The ST is preparing to absorb the impact of the 50% budget reduction on the Flight Operation Team at GSFC. At this time, the main impact has been a small increase in lost data (1–2%) as a result of the absence of operators to attempt immediate recovery. The ST also approved plans for ASTER’s contribution to the Terra power mitigation plan, and the recommendation has been forwarded to the Terra Project Scientist and the Flight Operations Team.
Conclusion
The 54th ASTER ST Meeting successfully covered all critical issues introduced during the Opening Plenary Session. The ST worked on formulating priorities for reduction of ASTER instrument operations in response to possible future Terra power reductions. During working group sessions, participants received updates on a variety of topics (e.g., instrument scheduling, instrument performance, archiving plans, and new applications). Although this may be the last Joint U.S./Japan ASTER ST Meeting, the 55th joint meeting was tentatively scheduled for May 2026.
Acknowledgments
The lead author’s work on this article was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.
Michael Abrams
NASA/Jet Propulsion Laboratory/California Institute of Technology
mjabrams@jpl.nasa.gov
Yasushi Yamaguchi
Nagoya University/Japan Science and Technology Agency
yasushi@nagoya-u.jp
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Last Updated Aug 18, 2025 Related Terms
Earth Science View the full article
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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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By NASA
The crew of NASA’s SpaceX Crew-11 mission pose for a photo during a training session.Credit: SpaceX NASA astronauts Michael Finke and Zena Cardman will connect with students in Minnesota as they answer prerecorded science, technology, engineering, and mathematics (STEM) questions aboard the International Space Station.
The Earth-to-space call will begin at 11 a.m. EDT on Wednesday, Aug. 20, and will stream live on the agency’s Learn With NASA YouTube channel.
Media interested in covering the event must RSVP by 5 p.m., Tuesday, Aug. 19, to Elizabeth Ross at: 952-838-1340 or elizabeth.ross@pacer.org.
The PACER center will host this event in Bloomington for students in their Tech for Teens program. The organization aims to improve educational opportunities and enhance the quality of life for children and young adults with disabilities and their families. The goal of this event is to help educate and inspire teens with disabilities to consider opportunities in STEM fields.
For nearly 25 years, astronauts have continuously lived and worked aboard the space station, testing technologies, performing science, and developing skills needed to explore farther from Earth. Astronauts communicate with NASA’s Mission Control Center in Houston 24 hours a day through SCaN’s (Space Communications and Navigation) Near Space Network.
Research and technology investigations taking place aboard the space station benefit people on Earth and lay the groundwork for other agency missions. As part of NASA’s Artemis campaign, the agency will send astronauts to the Moon to prepare for future human exploration of Mars; inspiring Golden Age explorers and ensuring the United States continues to lead in space exploration and discovery.
See more information on NASA in-flight downlinks at:
https://www.nasa.gov/stemonstation
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Gerelle Dodson
Headquarters, Washington
202-358-1600
gerelle.q.dodson@nasa.gov
Sandra Jones
Johnson Space Center, Houston
281-483-511
sandra.p.jones@nasa.gov
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Last Updated Aug 15, 2025 LocationNASA Headquarters Related Terms
International Space Station (ISS) Artemis ISS Research STEM Engagement at NASA View the full article
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By NASA
A member of the space crop production team prepares materials for Veggie seed pillows inside the Space Systems Processing Facility at NASA’s Kennedy Space Center. NASA/Cory S Huston When the Crew-11 astronauts launched to the International Space Station on August 1, 2025, they carried with them another chapter in space farming: the latest VEG-03 experiments, complete with seed pillows ready for planting.
Growing plants provides nutrition for astronauts, as well as psychological benefits that help maintain crew morale during missions.
During VEG-03 MNO, astronauts will be able to choose what they want to grow from a seed library including Wasabi mustard greens, Red Russian Kale, and Dragoon lettuce.
From Seed to Space Salad
The experiment takes place inside Veggie, a chamber about the size of carry-on luggage. The system uses red, blue, and green LED lights to provide the right spectrum for plant growth. Clear flexible bellows — accordion-like walls that expand to accommodate maturing plants — create a semi-controlled environment around the growing area.
Astronauts plant thin strips containing their selected seeds into fabric “seed pillows” filled with a special clay-based growing medium and controlled-release fertilizer. The clay, similar to what’s used on baseball fields, helps distribute water and air around the roots in the microgravity environment.
Crew members will monitor the plants, add water as needed, and document growth through regular photographs. At harvest time, astronauts will eat some of the fresh produce while freezing other samples for return to Earth, where scientists will analyze their nutritional content and safety.
How this benefits space exploration
Fresh food will become critical as astronauts venture farther from Earth on missions to the Moon and Mars. NASA aims to validate different kinds of crops to add variety to astronaut diets during long-duration space exploration missions, while giving crew members more control over what they grow and eat.
How this benefits humanity
The techniques developed for growing crops in space’s challenging conditions may also improve agricultural practices on Earth. Indoor crop cultivation approaches similar to what astronauts do in Veggie might also be adapted for horticultural therapy programs, giving elderly or disabled individuals new ways to experience gardening when traditional methods aren’t accessible.
Related Resources
VEG-03 MNO on the Space Station Research Explorer
Veggie Vegetable Product System
Veggie Plant Growth System Activated on International Space Station
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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