Jump to content
Join the Alien Search, login or register FREE on Aliens and Space Forum
Members Can Post Anonymously On This Site

A Decade of Global Water Cycle Monitoring: NASA Soil Moisture Active Passive Mission

NASA

By NASA
in NASA

 Share

Recommended Posts

  • Publishers
NASA Mentor

NASA

Posted
  • Publishers
Posted
Feature Article header

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.

SMAP figure 1
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.

SMAP figure 2
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.

SMAP 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.  

SMAP figure 4
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.

SMAP 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.

SMAP figure 6
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.

Black Separator Line

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.

Black Separator Line

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

Share

Details

Last Updated
Aug 18, 2025

Related Terms

View the full article

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
 Share
Go to topic listing

  • Similar Topics

    • NASA
      NASA Sets Coverage for SpaceX 33rd Station Resupply Launch, Arrival
      By NASA
      The SpaceX Falcon 9 rocket carrying the Dragon spacecraft lifts off from Launch Complex 39A at NASA’s Kennedy Space Center in Florida on Monday, April 21, 2025, on the company’s 32nd commercial resupply services mission for the agency to the International Space Station. Liftoff was at 4:15 a.m. EDT. SpaceX NASA and SpaceX are targeting 2:45 a.m. EDT, Sunday, Aug. 24, for the next launch to deliver science investigations, supplies, and equipment to the International Space Station. This is the 33rd SpaceX commercial resupply services mission to the orbital laboratory for NASA.
      Filled with more than 5,000 pounds of supplies, a SpaceX Dragon spacecraft on a Falcon 9 rocket will lift off from Space Launch Complex 40 at Cape Canaveral Space Force Station in Florida. Dragon will dock autonomously about 7:30 a.m. on Monday, Aug. 25, to the forward port of the space station’s Harmony module.
      Watch agency launch and arrival coverage on NASA+, Netflix, Amazon Prime, and more. Learn how to watch NASA content through a variety of platforms, including social media.
      In addition to food, supplies, and equipment for the crew, Dragon will deliver several experiments, including bone-forming stem cells for studying bone loss prevention and materials to 3D print medical implants that could advance treatments for nerve damage on Earth. Dragon also will deliver bioprinted liver tissue to study blood vessel development in microgravity and supplies to 3D print metal cubes in space. Research conducted aboard the space station advances future space exploration – including Artemis missions to the Moon and astronaut missions Mars – and provides multiple benefits to humanity.
      In addition, Dragon will perform a reboost demonstration of station to maintain its current altitude. The hardware, located in the trunk of Dragon, contains an independent propellant system separate from the spacecraft to fuel two Draco engines using existing hardware and propellant system design. The boost kit will demonstrate the capability to help sustain the orbiting lab’s altitude starting in September with a series of burns planned periodically throughout the fall of 2025. During NASA’s SpaceX 31st commercial resupply services mission, the Dragon spacecraft performed its first demonstration of these capabilities on Nov. 8, 2024.
      The Dragon spacecraft is scheduled to remain at the space station until December when it will depart and return to Earth with research and cargo, splashing down in the Pacific Ocean off the coast of California.
      NASA’s mission coverage is as follows (all times Eastern and subject to change based on real-time operations):
      Tuesday, Aug. 19:
      1 p.m. – International Space Station National Laboratory Science Webinar with the following participants:
      Heidi Parris, associate program scientist, NASA’s International Space Station Program Research Office Michael Roberts, chief scientific officer, International Space Station National Laboratory James Yoo, assistant director, Wake Forest Institute of Regenerative Medicine Tony James, chief architect for science and space, Red Hat Abba Zubair, medical director and scientist, Mayo Clinic Arun Sharma, director, Center for Space Medicine Research, Cedars-Sinai Medical Center Media who wish to participate must register for Zoom access no later than one hour before the start of the webinar.
      The conference will stream live on the International Space Station National Lab’s website.
      Friday, Aug. 22:
      11:30 a.m. – Prelaunch media teleconference with the following participants:
      Bill Spetch, operations integration manager, NASA’s International Space Station Program Heidi Parris, associate program scientist, NASA’s International Space Station Program Research Office Sarah Walker, director, Dragon Mission Management, SpaceX Media who wish to participate by phone must request dial-in information by 10 a.m. Aug. 22, by emailing NASA Kennedy Space Center’s newsroom at: ksc-newsroom@mail.nasa.gov.
      Audio of the media teleconference will stream live on the agency’s YouTube channel.
      Sunday, Aug. 24
      2:25 a.m. – Launch coverage begins on NASA+, Netflix, and Amazon Prime.
      2:45 a.m. – Launch
      Monday, Aug. 25:
      6 a.m. – Arrival coverage begins on NASA+, Netflix, and Amazon Prime.
      7:30 a.m. – Docking
      NASA website launch coverage
      Launch day coverage of the mission will be available on the NASA website. Coverage will include live streaming and blog updates beginning no earlier than 2:25 a.m. Sunday, Aug. 24, as the countdown milestones occur. On-demand streaming video on NASA+ and photos of the launch will be available shortly after liftoff. For questions about countdown coverage, contact the NASA Kennedy newsroom at 321-867-2468. Follow countdown coverage on our International Space Station blog for updates.
      Attend Launch Virtually
      Members of the public can register to attend this launch virtually. NASA’s virtual guest program for this mission also includes curated launch resources, notifications about related opportunities or changes, and a stamp for the NASA virtual guest passport following launch.
      Watch, Engage on Social Media Let people know you’re watching the mission on X, Facebook, and Instagram by following and tagging these accounts:
      X: @NASA, @NASAKennedy, @NASASocial, @Space_Station, @ISS_CASIS
      Facebook: NASA, NASAKennedy, ISS, ISS National Lab
      Instagram: @NASA, @NASAKennedy, @ISS, @ISSNationalLab
      Coverage en Espanol
      Did you know NASA has a Spanish section called NASA en Espanol? Check out NASA en Espanol on X, Instagram, Facebook, and YouTube for additional mission coverage.
      Para obtener información sobre cobertura en español en el Centro Espacial Kennedy o si desea solicitar entrevistas en español, comuníquese con Antonia Jaramillo o Messod Bendayan a: antonia.jaramillobotero@nasa.gov o messod.c.bendayan@nasa.gov.
      Learn more about the mission at:
      https://www.nasa.gov/mission/nasas-spacex-crs-33/
      -end-
      Joshua Finch
      Headquarters, Washington
      202-358-1100
      joshua.a.finch@nasa.gov
      Steven Siceloff
      Kennedy Space Center, Fla.
      321-876-2468
      steven.p.siceloff@nasa.gov
      Sandra Jones / Joseph Zakrzewski
      Johnson Space Center, Houston
      281-483-5111
      sandra.p.jones@nasa.gov / joseph.a.zakrzewskI@nasa.gov
      Share
      Details
      Last Updated Aug 18, 2025 LocationNASA Headquarters Related Terms
      SpaceX Commercial Resupply Commercial Resupply International Space Station (ISS) Johnson Space Center Kennedy Space Center NASA Headquarters View the full article
    • NASA
      Bone Loss Research Launches Aboard NASA’s SpaceX-33 Resupply Mission
      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.
      View the full article
    • NASA
      NASA, Army National Guard Partner on Flight Training for Moon Landing
      By NASA
      5 Min Read NASA, Army National Guard Partner on Flight Training for Moon Landing
      By Corinne Beckinger
      When Artemis astronauts land on the Moon’s South Pole in a commercial human landing system, they will encounter a landscape pockmarked with deep craters, sloped connecting ridges, and harsh lighting conditions. The Moon’s lack of contrast, combined with its rolling terrain, will also pose a challenge, making it difficult for astronauts to overcome visual illusions on the lunar surface.
      NASA astronaut Bob Hines (left) and Colorado Army National Guard HAATS instructor Ethan Jacobs practice landing procedures in the Rocky Mountains of Colorado in April 2025. Depending on the season, the snowy or dusty conditions can cause visual obstruction. Lunar dust can cause similar visual impairment during future crewed missions. In the mountains of northern Colorado, NASA and the U.S. Army National Guard are using military helicopters to develop a foundational lunar landersimulated flight training course to help astronauts practice flight and landing procedures for the Moon. 
      For decades, military helicopter pilots have trained at the HAATS (High-Altitude Army National Guard Aviation Training Site) in Gypsum, Colorado. In 2021, NASA and the Colorado Army National Guard began working together to develop a course specifically for the next generation of lunar explorers.
      That NASA-specific course is scheduled to be finalized in August 2025, marking an important milestone for Artemis crewed landings training efforts.
      “NASA is using a three-pronged approach with motion-based simulation, in-flight lunar landing analog training, and in-flight lunar simulation to build out its foundational training for Artemis Moon landings,” said NASA astronaut Doug Wheelock, who helped coordinate the training program. “Helicopters at or above 10,000 feet are not really efficient in the thin air, forcing us into operating with very thin power margins similar to the Apollo astronauts having to manage energy and momentum to land safely. The operations along with the terrain at the HAATS course in Colorado’s Rocky Mountains provide a valuable, real-world opportunity for Artemis astronauts to practice flying and landing in conditions similar to maneuvering a lander in the lunar environment.”
      NASA astronaut Raja Chari participates in the HAATS course in April 2025. Since 2021, 22 NASA astronauts and one ESA (European Space Agency) astronaut have participated and evaluated the course based on functionality and Artemis mission needs. NASA/Laura Kiker NASA astronaut Raja Chari participates in the HAATS course in April 2025. Since 2021, 22 NASA astronauts and one ESA (European Space Agency) astronaut have participated and evaluated the course based on functionality and Artemis mission needs. NASA/Corinne Beckinger NASA’s human landing systems that will safely transport astronauts to and from the Moon’s surface will be provided by SpaceX and Blue Origin.
      NASA’s Artemis III mission will build on earlier test flights and add new capabilities, including SpaceX’s Starship Human Landing System and advanced spacesuits, to send the first astronauts to explore the lunar South Pole and prepare humanity to go to Mars.
      While each industry provider is responsible for training Artemis astronauts on its specific lander, NASA is establishing foundational training to help prepare astronauts for crewed flights.
      Flight training opportunities like this are vital to mission success and crew safety.”
      Doug Wheelock
      NASA Astronaut
      “Over the last few years, NASA and the Army National Guard have worked closely to evaluate training procedures and landing zone areas, incorporating accounts from Apollo astronauts,” Wheelock said. “During training flights at HAATS, astronauts can experience the visual illusions, cross-cockpit communication, and degraded visibility they may experience navigating to their landing zone near the lunar south pole. Flight training opportunities like this are vital to mission success and crew safety.”
      Paired with trained instructors from the Army National Guard, astronauts fly to mountaintops and valleys in a range of aircraft, including LUH-72 Lakotas, CH-47 Chinooks, and UH-60 Black Hawks.
      While one astronaut pilots the aircraft, an astronaut in the back charts the landing area, marking key landmarks, identifying potential hazards, and helping to track the flight path. Throughout the week-long course, the landing zones and situations become more challenging, allowing astronauts to experience team dynamics and practice communication skills they will need to land on the Moon.
      “Our full-time Colorado Army National Guard pilots have thousands of flight hours navigating the Rocky Mountains at altitudes ranging from 6,500 to 14,200 feet, and we are reaching new heights by providing realistic and relevant training with NASA for Artemis,” said first sergeant Joshua Smith of the HAATS program. “Our Colorado Army National Guard pilots may not fly around the Moon, but we wear our motto, de monitbus ad astra — from the mountains to the stars — with pride.”
      Fast Facts
      On the Moon’s South Pole, the Sun is never more than 1.5 degrees above or below the horizon. With the Sun at such a low angle and with only a thin exosphere, shadows are stark, and astronauts may find it difficult to determine distances and heights.

      The Moon’s atmosphere is extremely thin, with few particles, and is called an exosphere. The Moon’s exosphere is thin enough to glow in sunlight, which has been observed by spacecraft and some of the Apollo astronauts. The Moon’s surface is challenging to land on. There are inactive volcanoes, bounders, large basins, craters, and cracks in the Moon’s crust, caused by the Earth’s gravity tugging on the Moon. Moon dust can also obscure the view from the windows of a commercial human landing system, and affect sensors that relay important information, such as altitude and velocity, to astronauts. Through the Artemis campaign, NASA will send astronauts to explore the Moon for scientific discovery, economic benefits, and to build the foundation for the first crewed missions to Mars – for the benefit of all. 
      For more information about Artemis visit:
      https://www.nasa.gov/artemis
      Share
      Details
      Last Updated Aug 18, 2025 EditorBeth RidgewayContactCorinne M. Beckingercorinne.m.beckinger@nasa.govLocationMarshall Space Flight Center Related Terms
      Human Lander Challenge General Human Landing System Program Marshall Space Flight Center Explore More
      3 min read Human Rating and NASA-STD-3001
      Article 3 days ago 3 min read NASA Seeks Proposals for 2026 Human Exploration Rover Challenge 
      Article 3 days ago 4 min read NASA IXPE’s ‘Heartbeat Black Hole’ Measurements Challenge Current Theories
      Article 6 days ago Keep Exploring Discover More Topics From NASA
      Artemis
      Human Landing System
      Earth’s Moon
      The Moon makes Earth more livable, sets the rhythm of ocean tides, and keeps a record of our solar system’s…
      Artemis III
      View the full article
    • NASA
      NASA Invites Media to Northrop Grumman CRS-23 Station Resupply Launch
      By NASA
      Northrop Grumman’s Cygnus spacecraft, atop a SpaceX Falcon 9 rocket, soars from Space Launch Complex 40 at Cape Canaveral Space Force Station in Florida on Aug. 4, 2024, for Northrop Grumman’s 21st Commercial Resupply Services mission for NASA.Credit: SpaceX Media accreditation is open for the next launch to deliver NASA science investigations, supplies, and equipment to the International Space Station. A Northrop Grumman Cygnus spacecraft will launch to the orbital laboratory on a SpaceX Falcon 9 rocket for NASA.
      The mission is known as NASA’s Northrop Grumman Commercial Resupply Services 23, or Northrop Grumman CRS-23. Liftoff is targeted for mid-September from Space Launch Complex 40 at Cape Canaveral Space Force Station in Florida.
      Following launch, astronauts aboard the space station will use the Canadarm2 to grapple Cygnus, and the spacecraft will be installed robotically to the Unity module’s Earth-facing port for cargo unloading. The spacecraft will remain at the space station for more than two months.
      Credentialing to cover prelaunch and launch activities is open to U.S. media. The application deadline for U.S. citizens is 11:59 p.m. EDT, Wednesday, Aug. 27. All accreditation requests must be submitted online at:
      https://media.ksc.nasa.gov
      Credentialed media will receive a confirmation email upon approval. NASA’s media accreditation policy is available online. For questions about accreditation, or to request special logistical support, email: ksc-media-accreditat@mail.nasa.gov. For other questions, please contact NASA’s Kennedy Space Center newsroom at: 321-867-2468.
      Para obtener información sobre cobertura en español en el Centro Espacial Kennedy o si desea solicitor entrevistas en español, comuníquese con Antonia Jaramillo o Messod Bendayan a: antonia.jaramillobotero@nasa.gov o messod.c.bendayan@nasa.gov.
      This is the 23rd spacecraft built to deliver goods to the International Space Station. In March, NASA and Northrop Grumman moved up the company’s Commercial Resupply Services-23 mission to September following damage to the Cygnus Pressurized Cargo Module during shipping for the company’s Commercial Resupply Services-22 flight.
      Each resupply mission to the station delivers scientific investigations in the areas of biology and biotechnology, Earth and space science, physical sciences, and technology development and demonstrations. Cargo resupply from U.S. companies ensures a national capability to deliver scientific research to the space station, increasing NASA’s ability to conduct new investigations aboard humanity’s laboratory in space.
      In addition to food, supplies, and equipment for the crew, Cygnus will deliver research, including materials to produce semiconductor crystals in space and equipment to develop improvements for cryogenic fuel tanks. Cygnus also will deliver a specialized UV light system to prevent biofilm growth and supplies to produce pharmaceutical crystals that could treat cancer and other diseases.
      The International Space Station is a convergence of science, technology, and human innovation that enables research not possible on Earth. For almost 25 years, humans have continuously lived and worked aboard the International Space Station, advancing scientific knowledge and demonstrating new technologies that enable us to prepare for human exploration of the Moon and Mars.
      Learn more about NASA’s commercial resupply missions at:
      https://www.nasa.gov/station
      -end-
      Josh Finch
      Headquarters, Washington
      202-358-1100
      joshua.a.finch@nasa.gov
      Steven Siceloff
      Kennedy Space Center, Fla.
      321-876-2468
      steven.p.siceloff@nasa.gov
      Sandra Jones / Joseph Zakrzewski
      Johnson Space Center, Houston
      281-483-5111
      sandra.p.jones@nasa.gov / joseph.a.zakrzewski@nasa.gov
      Share
      Details
      Last Updated Aug 18, 2025 EditorJessica TaveauLocationNASA Headquarters Related Terms
      Commercial Resupply International Space Station (ISS) ISS Research Northrop Grumman Commercial Resupply View the full article
    • NASA
      NASA Challenge Winners Cook Up New Industry Developments
      By NASA
      4 min read
      Preparations for Next Moonwalk Simulations Underway (and Underwater)
      NuCLEUS, developed by Interstellar Lab, is an autonomous system that grows microgreens, vegetables, and more for astronauts to eat in space.Interstellar Lab NASA invests in technologies that have the potential to revolutionize space exploration, including the way astronauts live in space. Through the Deep Space Food Challenge, NASA, in partnership with CSA (Canadian Space Agency), sought novel food production systems that could provide long-duration human space exploration missions with safe, nutritious, and tasty food. Three winners selected last summer are now taking their technology to new heights – figuratively and literally – through commercial partnerships. 
      Interstellar Lab of Merritt Island, Florida, won the challenge’s $750,000 grand prize for its food production system NuCLEUS (Nutritional Closed-Loop Eco-Unit System), by demonstrating an autonomous operation growing microgreens, vegetables, and mushrooms, as well as sustaining insects for use in an astronaut’s diet. To address the requirements of the NASA challenge, NuCLEUS includes an irrigation system that sustains crop growth with minimal human intervention. This end-to-end system supplies fresh ingredients to support astronauts’ health and happiness, with an eye toward what the future of dining on deep space missions to Mars and the Moon may look like. 
      Since the close of the challenge, Interstellar Lab has partnered with aerospace company Vast to integrate a spinoff of NuCLEUS, called Eden 1.0, on Haven-1, a planned commercial space station. Eden 1.0 is a plant growth unit designed to conduct research on plants in a microgravity environment using functions directly stemming from NuCLEUS.  
      “The NASA Deep Space Food Challenge was a pivotal catalyst for Interstellar Lab, driving us to refine our NuCLEUS system and directly shaping the development of Eden 1.0, setting the stage for breakthroughs in plant growth research to sustain life both in space and on Earth,” said Barbara Belvisi, founder and CEO of Interstellar Lab. 
      Fuanyi Fobellah, one of the “Simunauts” from The Ohio State University who tested food production technologies as part of the Deep Space Food Challenge, removes a cooked omelet from the SATED appliance.NASA/Savannah Bullard Team SATED (Safe Appliance, Tidy, Efficient & Delicious) of Boulder, Colorado, earned a $250,000 second prize for its namesake appliance, which creates an artificial gravitational force that presses food ingredients against its heated inner surface for cooking. The technology was developed by Jim Sears, who entered the contest as a one-person team and has since founded the small business SATED Space LLC.  
      At the challenge finale event, the technology was introduced to the team of world-renowned chef and restaurant owner, José Andrés. The SATED technology is undergoing testing with the José Andrés Group, which could add to existing space food recipes that include lemon cake, pizza, and quiche. The SATED team also is exploring partnerships to expand the list of ingredients compatible with the appliance, such as synthetic cooking oils safe for space. 
      Delicious food was a top priority in the Deep Space Food Challenge. Sears noted the importance of food that is more than mere sustenance. “When extremely high performance is required, and the situations are demanding, tough, and lonely, the thing that pulls it all together and makes people operate at their best is eating fresh cooked food in community.” 
      Team Nolux won a $250,000 second-place prize for its Nolux food system that uses artificial photosynthesis to grow ingredients that could be used by astronauts in space.OSU/CFAES/Kenneth Chamberlain Team Nolux, formed from faculty members, graduate, and undergraduate students from the University of California, Riverside, also won a $250,000 second prize for its artificial photosynthesis system. The Nolux system – whose name means “no light” – grows plant and fungal-based foods in a dark chamber using acetate to chemically stimulate photosynthesis without light, a capability that could prove valuable in space with limited access to sunlight.  
      Some members of the Nolux team are now commercializing select aspects of the technology developed during the challenge. These efforts are being pursued through a newly incorporated company focused on refining the technology and exploring market applications. 
      A competition inspired by NASA’s Deep Space Food Challenge will open this fall.  
      Stay tuned for more information: https://www.nasa.gov/prizes-challenges-and-crowdsourcing/centennial-challenges/  
      View the full article

  • Check out these Videos

×
×
  • Create New...