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Summary of the 2023 GRACE Follow-On Science Team Meeting

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28 min read

Summary of the 2023 GRACE Follow-On Science Team Meeting

Felix Landerer, NASA/Jet Propulsion Laboratory, felix.w.landerer@jpl.nasa.gov

Introduction

In October 2023, the annual gathering of the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On [G-FO] Science Team took place in Boulder, CO, hosted at University Corporation for Atmospheric Research’s (UCAR) Center Green campus. The event had 70 in-person participant and an additional 52 online participants – see Photo. G-FO is a U.S.–German collaboration between NASA and the Helmholtz Centre Potsdam GeoForschungsZentrum (GFZ) [German Research Centre for Geosciences].

GRACE team photo
Photo: Pictured here are the in-person attendees of the 2023 GRACE-FO Science Team. Another 52 people participated online.
Image credit: Felix Landerer/JPL

The meeting agenda featured 15-minute presentations over three days, describing new findings from G-FO observations and the combined GRACE and GRACE-FO [G/G-FO] climate data record that now spans over 21 years (2002–2023). 

The meeting began with the customary G-FO project status session, covering programmatic mission and flight segment technical updates, future mission plans, and descriptions of the latest data released from the GRACE Science Data System (SDS) centers. Subsequent sessions featured more than 53 contributed presentations covering analyses, algorithms, and science results by Science Team members and attendees, totaling 57 oral and 5 poster presentations. Many of the presentations are posted on the GRACE website. While this summary will cover all the content on the agenda of the meeting – it does do so in an exact linear fashion. It begins with a G-FO mission status update, followed by key highlights from the contributed analysis and science presentations.

Status of GRACE Follow-On

Since their launch on May 22, 2018, the twin G-FO satellites have been tracking Earth’s water movements and global surface mass changes that arise from climatic, anthropogenic, and tectonic changes. G-FO also enables new insights into variations of ice sheet and glacier mass, land water storage, as well as changes in sea level and ocean currents. These measurements have important applications and implications for everyday life. The impact of these data is underscored by the publication of over 6000 scientific papers – an average of 5 new publications per week – that have established G/G-FO as a leading Earth Science mission.

In May 2023, G-FO successfully completed its Prime Mission phase that lasted five years after launch. G-FO was among the missions that went through the 2023 NASA Earth Science Senior Review. The NASA project team submitted its response in spring of 2023 to extend mission operations through 2026. The proposal received overall Excellent score, highlighting the unique utility the data provide for Earth Science research and societal applications. However, the G-FO project’s NASA budget will be reduced (compared to the previous baseline) by 15% in fiscal year (FY) 2024 and 24% in FY 2025 and 2026 due to the overall budget constraints that NASA is facing. The G-FO team remains confident in its ability to continue delivering high-value and high-impact science data products – prioritizing science operations management and data latency over data reprocessing campaigns. Both NASA and GFZ had already formally committed to extending their collaboration on G-FO mission operations and data processing through the end of 2026 via a Memorandum of Understanding.

As of December 2023, the G-FO project team has processed and released 62 monthly gravity fields – the most recent being for October 2023 (at the time of this writing). The primary mission objective for G-FO is to provide continuity for the monthly GRACE mass-change observations (2002–2017) via its Microwave Interferometer (MWI) intersatellite range-change observations. G-FO also demonstrated a novel technology demonstration Laser-Ranging Interferometer (LRI) for more accurate satellite-to-satellite ranging observations for future GRACE-like missions. The LRI has been successfully operated in parallel with the MWI for most of the mission, delivering excellent quality data. LRI-based monthly gravity and mass change fields covering the period from mid-2018 to mid-2023 have been made available by the SDS teams for further analysis and study by the science community. 

Programmatic, Mission, and Operations Updates

The meeting began with Frank Flechtner [GFZ–German G-FO Project Manager] and Felix Landerer [NASA/Jet Propulsion Laboratory (JPL)—U.S. G-FO Project Scientist] giving welcoming remarks, followed by detailed assessments of the G-FO mission and operations status from the core SDS centers and flight operations teams.

GRACE Follow-On Project Status

Felix Landerer gave an overview of the G-FO satellites and the science data system performance. He reported that G-FO continues to meet its goal of extending the GRACE mass-change and gravity data record at equivalent precision and spatiotemporal sampling. 

Since the previous STM in October 2022, the overall G-FO science instrument performance has been stable, and the SDS team continued to deliver a gapless monthly data record to users ahead of schedule (on average, within 43 days instead of the 60-day requirement). Improving the data calibrations of the accelerometer measurements – which are noise contaminated on one of the two G-FO spacecraft – remains a core focus of the project SDS team. To this end, an improved calibration approach that reduced data errors by 10–20% has been developed and will be operationalized by the team in the coming months. 

Landerer reported that, as forecasted, the current Solar Cycle 25 has gained in strength through 2023 and will continue to do so through 2024 before subsiding again. The resulting higher non-gravitational forces acting on the satellites need to be properly accounted for in the accelerometer data processing. 

He also noted that small thruster leaks in the satellites cold gas propulsion system have been closely monitored since 2021. To ensure stable data collection and sufficient lifetime margin to achieve continuity with the proposed successor mission GRACE-Continuity, or GRACE-C (which is the new name for the Earth System Observatory Mass Change mission scheduled for launch no earlier than 2028), the G-FO project team, in conjunction with guidance from the satellite manufacturer Airbus and the German Space Operations Center, decided to adjust the operational data collection mode of G-FO to a wide pointing mode – which means that the two spacecraft are allowed to deviate from their relative line-of-sight pointing by up to 2°, whereas the previous pointing angles were 100 times smaller. This operational change necessitates fewer thruster firings, which in turn reduces leaks and improves accelerometer calibrations – and thus leads to better overall science data quality. Due to the wide pointing, the LRI intersatellite ranging data collection has been suspended in this operational mode. However, the LRI instruments are still activated and fully functional. Landerer emphasized that reducing the leak ensures that the GRACE-FO mission will have sufficient fuel to remain operational up until GRACE-C launches.

Despite these operational challenges, Landerer said that the science data delivered by G-FO continues to provide excellent utility and insights into a rapidly changing Earth system. He briefly highlighted a few scientific and decision-support contributions and achievements of G-FO over the last year. These included: 

  • Monitoring California Groundwater. G-FO recorded the largest seasonal total water storage gains over California after the multiple atmospheric rivers made landfall during the 2022/2023 winter. Yet, peak water storage in May was below values observed 15–20 years ago – due to long-term, sustained groundwater declines. Going forward, the data will be invaluable to assess groundwater recharge rates and processes.
  • Tracking Polar Ice Mass Loss. G/G-FO measured net ice mass gains over Antarctica that began around 2021 due to snow accumulation mainly in East Antarctica, which offset the unabated mass loss of the West Antarctic ice sheet.

Subsequent science presentations presented in-depth analyses of these and other findings in the dedicated science sessions, some of which are summarized below. 

Landerer also highlighted the expanding portfolio of open science contributions that the project team is supporting: Jupyter notebooks are part of an expanding GRACE Open Science toolbox with the goal to expand this toolbox with input from the Science Team and user community in the coming years. In addition, easy-to-use browser data portals at JPL and GFZ have been key to expand the science and applications user community that increasingly use the Level-3 and higher data products in decision support contexts (e.g., for drought monitoring and water resources management).

A series of status reports on programmatic G-FO mission operations, science operations, and SDS processing followed the opening presentations. Krzysztof Snopek [GFZ] reported on the ground and mission operations at the German Space Operations Center (GSOC), which is responsible for G-FO spacecraft operations. All essential flight operations, software updates, and planned calibrations were successfully scheduled and carried out by GSOC. Himanshu Save [University of Texas, Center for Space Research (CSR)] provided the science operations assessment. He described the evolving Solar Cycle 25 and its influence on the G-FO spacecraft, the mission’s fuel budget, and adjusted operational procedures and modes (such as the already-mentioned ‘wide’ pointing mode). Christopher McCullough [JPL] reviewed the status of G/G-FO Level 1 processing at JPL, detailing additional improvements made in the accelerometer calibrations. The team is using the noisy accelerometer data on one satellite and retrieving improved science information from it.

A representative from each of the G-FO mission SDS centers – which includes JPL, GFZ, CSR, and GSFC – summarized the status of the latest gravity-field and mass change data products [RL06.X L2], including an overview of background dealiasing models and the GFZ GravIS portal, the updated JPL mascon data product, new data-processing strategies, e.g., via range acceleration [CSR], and the status of ancillary Satellite-Laser-Ranging (SLR) data processing and dedicated G/G-FO products [GSFC].

Following the project team’s status presentations, there was a 30-minute session to answer questions from the science community and discuss in more detail the mission performance, near-term operations and data processing plans, as well as to gather suggestions and feedback from the community. 

Science Presentations

The remainder of the sessions in the meeting were open-submission science sessions, each of which centered around different thematic topics, including: G/G-FO analysis techniques and next generation gravity mission (NGGM) concept studies, and science analysis of mass-transport data in the fields of glaciology, oceanography, hydrology, and solid-Earth physics. As has been the case in previous years, the presenters underscored the value of interdisciplinary and multi-instrument analyses that utilize the unique complementary value of G/G-FO mass-change observations in combination with other remote sensing data (e.g., satellite altimetry or precipitation observations) and in situ data (e.g., surface deformation or ocean temperature profiles). Such hydrogeodetic combinations yield improved spatial and temporal resolutions that enable advances in Earth system process understanding, which increasingly advance societal applications of science results in support of NASA’s programmatic focus on Earth Science to Action, which seeks to “advance and integrate Earth science knowledge to empower humanity to create a more resilient world.”

Section A: GRACE and GRACE-FO Geodesy

The project status reports presented under the previous heading were part of the first section of the agenda (Session A1) as were two additional sessions: Analysis Techniques and Intercomparisons (Session A2) and NGGM and Bridging the Gap (Session A3), which focused on plans, concepts, and technologies being developed for future gravity missions. Highlights from each of these two sessions follow in the next two subsections. 

Analysis Techniques and Inter-comparisons

This session featured 15 presentations by the SDS centers and ST members on progress in instrument data calibrations and novel data processing algorithms and methods, including data-fusion with other observations.

Representatives from G/G-FO processing centers presented updated gravity-field time-series data, which capitalize on improved parameterizations, better instrument error characterizations (e.g., from star cameras, accelerometers, or ranging instruments) and background models (e.g., for tides) for improved monthly mass change data and uncertainty quantification. The highly accurate LRI data provides further opportunities to identify and characterize measurement system errors, which can be exploited for G-FO data processing but is also informative in the development of the future GRACE-C mission. However, it was also shown that several metrics used in identifying gravitational errors are sensitive to the estimated satellite trajectory, and consequently a sufficient understanding of the orbital trajectory is necessary to make accurate adjustments to the gravity field based on satellite observations.

The G/G-FO data products make use of ground-based geodetic observations, such as satellite laser-ranging (SLR) to a network of dedicated SLR satellites, which can be used to extend the G/G-FO interannual data record back to ~1994 – albeit at a much-reduced spatial resolution. Additionally, SLR data provide an important validation and performance assessment opportunity for G/G-FO observations. In that regard one presenter showed results indicating the recent G-FO accelerometer updates have indeed resulted in better gravity and mass change fields. Other speakers discussed the value and potential for improvement that could be achieved by combining G-FO and SLR observations more formally to exploit the data strengths of the different observation types in an optimal way. Such approaches could reduce uncertainties in global ocean and land ice mass changes. Furthermore, deployment of stable, long-term ocean bottom pressure (OBP) recorders in the Arctic Ocean in 2022 has enabled progress on G/G-FO OBP data validation. The data from these OBP recorders are entirely independent of G/G-FO observations and are thus very valuable to assess the satellite data record. An initial comparison between 1.5 years of OBP data and various G-FO OBP products suggest excellent agreement.

The data collected from G/G-FO has a native resolution of about 300 km (~186 mi). By jointly analyzing these G/G-FO data with higher-resolution surface elevation changes from a multimission synthesis of radar and laser satellite altimeters, net mass changes can be effectively downscaled (within a Bayesian framework) to less than 20 km (~12 mi) resolution, which is sufficiently high resolution to resolve individual ice streams in Antarctica that cannot be separated using G/G-FO data alone.

NGGM and Bridging the Gap 

The presenters in this session provided status-update on the GRACE-C mission, a joint project between NASA and the Deutsches Zentrum für Luft- und Raumfahrt (DLR) [German Aerospace Center], as well as on future instrument developments and mission concepts. 

The 2017 NASA Earth Science Decadal Survey Report highlighted mass-transport monitoring through gravity change as one of five designated observables (i.e., top priorities for study) in Earth observations for the next decade in collaboration with international partners. The GRACE-C project successfully passed the NASA/JPL Mission Concept Review in June 2022, and the NASA Key Decision Point B review in September 2023 and is currently in its Phase B project definition phase. GRACE-C will be a single satellite pair based on a fully redundant LRI (as demonstrated on GRACE-FO) in a polar orbit at 500 km (~311 mi) altitude. To avoid a data gap after GFO, a launch date of no later than 2028 is targeted for GRACE-C.

Similarly, GFZ has been conducting model simulation studies to determine the value of adding a second satellite pair, dubbed Next-Generation Gravity Mission (NGGM) in Europe.  The experiments reveal that advanced parameterization techniques for improved de-aliasing of short-term mass variations can significantly reduce data errors and open the possibility for higher spatial and temporal resolution data products and science applications.

The technology demonstration LRI on G-FO has surpassed its performance requirements. With a LRI expected to be the primary instrument for the GRACE-C mission as well as other future GRACE-like missions, development of a new technique is required to provide long-term laser frequency knowledge to provide a scale correction factor to the geodesy measurement. The LRI-team presented updated results of a so-called scale factor measurement technique that allows the accurate determination of the laser frequency on-orbit that can meet the stringent GRACE-C mission requirements. This was achieved with a dual frequency modulation scheme, and a prototype electronics unit has been developed and tested, demonstrating performance better than the expected mission requirements. 

There were also reports on progress in technology development of low-frequency optomechanical accelerometers for geodetic applications. These highly-sensitive, compact, portable – and cost-effective – optomechanical inertial sensors build upon recent advances in optomechanics to measure accelerations with small form factors. The development of a sensor with lower cost, size, weight, and power – yet with GRACE-like performance – is a major achievement as these could be integrated into cost-effective mission designs, spacecraft miniaturization, simplified architectures, as well as for the deployment of constellations of satellite pairs flying at lower altitudes.

Section B: Geophysics and Climate Science

There were five sessions included in this section of the agenda, which are summarized in the subsections below as follows: Hydrology (Session B4), Cryosphere (Session B2), Solid Earth Sciences (Session B1), Oceanography (Session B3), and Multidisciplinary Science (Session B5). 

Hydrology 

This session, with 12 presentations, highlighted advances in hydrology research and applications using G/G-FO data enabled by the unique value of long, uninterrupted mass change climate data record. 

The topic of terrestrial water storage variations in California came up in several presentations, focusing on the see-saw swings between very wet and very dry years and the early impacts on groundwater recharge after the record-breaking snow accumulation during the 2022/2023 winter. The process of groundwater recharge – an important objective in the 2017 Earth Science Decadal Survey – is not well understood because of the challenges in observing infiltration of new water supply into the ground and the effects of rate of input, amount of input, and various aquifer characteristics. By combining observations of precipitation, snow water equivalent, surface water storage, ground surface deformation, and groundwater storage from G/G-FO, recharge behavior can be characterized in a natural experiment where source inputs are effectively not limited, but recharge capacity is limited. Results of studies shown during the meeting reveal that only a fraction of total available potential recharge can enter the aquifer, and that G/G-FO observations allow us to measure the effective aggregated recharge capacity and how it varies with several predictors. Another paper reported that subsurface water increases in California’s Sierra Nevada by 0.6 m (~2 ft) from October 2022 to June 2023, which represents 43% of the cumulative precipitation. 

Several presenters reported on efforts to advance concepts to downscale G/G-FO data to bring the information closer to decision-making scales and expand water-related applications, as well as to fill gaps and expand the data record with multisensor observations. One presenter described a new spectral approach that employs wavelet multiresolution analysis to combine seasonal terrestrial water storage change data from G/G-FO with those from global navigation satellite system (GNSS) ground station networks to downscale the observations to smaller hydrological basins and to better separate processes over complex topographical terrain. This method can also be used by fusing G/G-FO and hydrological model data [e.g., from NASA’s Global Land Data Assimilation System (GLDAS) models at continental scales]. Importantly, the method yields trends and long-term signals that match G/G-FO observations – a strength of the observing system. Another approach used a statistical Bayesian framework to incorporate G/G-FO observations and Soil Moisture Change data from different available sources [e.g., NASA’s Soil Moisture Active Passive (SMAP) mission] to obtain nonparametric likelihood functions that allow for downscaling. A statistical technique called cyclostationary empirical orthogonal function (CSEOF) analysis – which is used to interpret space-time variability in a large dataset – allowed researchers to fill short data gaps (~1 year) in G/G-FO record (e.g., between 2017 and 2018 – the gap between GRACE and GRACE–FO) without having any additional data. With the support of physically-related data (e.g., precipitation and temperature), CSEOFs can be used to reconstruct water changes into the past or fill larger data gaps. Such datasets improve understanding of trends and natural variability and anticipate future trends in response to climatic changes. 

Another presenter described a science study that found an apparent abrupt decline in temperate (non-ice) Terrestrial Water Storage (TWS) in 2015 to a new, lower regime that appears to be unique in the past 33 years. The triggering event for this new lower TWS regime appears to be the massive drought in Brazil in 2015. Subsequent droughts around the world (e.g., Europe, the western U.S., Canada, central Africa, and southern Brazil) have helped to keep TWS values depressed. Warm global sea surface temperatures, prevalent since 2015, have decreased rain accumulation over the continents, reducing TWS.

In the European Alps region, a G/G-FO data analysis found that glacier and ice changes are the major contributors to the observed signals. Overall, glaciers here have lost ice mass at rates between 1.4 to 2.2 Gt/year since 2002. Advances in spatial downscaling and data combinations are expected to allow for improved estimates and applications, including geological hazard monitoring.

In Northern Italy, accelerated groundwater loss has been detected using G/G-FO, well measurements, and vertical land motion observations. Since 2015, the groundwater loss has accelerated. Assuming a best-case scenario (conditions similar to 2007–2014), it could take 13–28 years for ground water storage to recover from recent long-term period of decline, thus setting the stage for prolonged drought conditions.

Since a pioneering study in 2014, it is well-established that G/G-FO observations of TWS are an effective means to estimate flood potential and flood risks due to water-saturated soil. Novel G/G-FO data processing schemes that exploit sub-monthly variations of total water storage enabled researchers to delineate basin-specific storage-discharge dynamics more accurately. They found that at submonthly timescales in many global basins, water storage (i.e., saturated soil) has more impact on whether a flood will occur than the amount of precipitation that falls. 

Along the Nile River, G/G-FO data were used to monitor water changes in crucial artificial reservoirs. These data indicate that water losses through underground-seepage over the geologically highly fractured region via a complex network of shear systems, faults, and fractures, are significant and could impact the delicate water balance in the region. A separate study focusing on nearby Southern Arabia found that intense tropical cyclones (wind speeds > 64 kph or ~40 mph) have doubled in the past decade compared to the preceding two, which resulted in significant recharge of the aquifers in the study area. The findings demonstrate the ability of G/G-FO to capture recharge signals and monitor aquifer systems in poorly gauged basins and highlight the significant role of tropical cyclones in recharging aquifers in arid Arabia.

Cryosphere

The five contributions in this session reported on new ice mass balance results of the Earth’s land-ice, as well as on novel data-combinations approaches that can improve the spatial resolution over G/G-FO-only data.

The Antarctica Ice Sheet contributes to the largest sea level rise potential and remains as the largest uncertainty source in the prediction of future sea levels. Data from G-FO and the Ice, Clouds and land Elevation Satellite–2 (ICESat-2) mission have been used to track ice sheet mass and height changes in Greenland and Antarctica, respectively. By combining the strengths of G-FO (gravity or mass change) and ICESat-2, (laser altimetry) data, a more accurate and less uncertain estimate of ice sheet mass changes can be achieved. This combination has led to a proposal for an enhanced iterative algorithm for deriving Antarctic mass balance, incorporating key technologies such as altimetry, gravity measurements, Global Positioning System (GPS) satellite data, and surface mass balance models. The study utilizes an effective density map derived from ICESat-2 and tests the algorithm’s sensitivity and uncertainty with synthetic data, considering realistic physical processes and variability. This approach aims to address discrepancies in estimating ice mass loss in East Antarctica and provides important guidance for optimizing future ground measurements (i.e., GPS station positions). Another presentation focused on understanding the differences in mass change recovered by the G/G-FO and IceSat-2 missions – both in terms of spatial distributions and total magnitudes – to ultimately determine a best combined estimate of ice sheet mass change leveraging the strengths of each mission. 

Temporal gravity field estimates from G/G-FO data reveal that the Antarctic ice sheet contributed approximately 6.1 mm (~0.2 in) to global sea level rise from 2002–2022, with a net loss of ~2150 GT of mass. While mass change accelerated during the GRACE era, it has decelerated during the GRACE-FO era – due to increased mass gain in East Antarctica. The deceleration is attributed to surface mass balance processes: annual precipitation and increased incidences of extreme weather events in East Antarctica, challenging predictions based on correlations with climate indices like Southern Annular Mode and El Niño Southern Oscillation.

A related study confirmed a pause in Antarctica’s mass loss, a non-accelerating mass loss in Greenland, and a steady loss from glaciers and ice caps away from the poles. The use of the LRI observations enabled novel submonthly analysis in key regions (including the Amundsen Sea Embayment of West Antarctica and the Pine Island/Thwaites basins) to gain more understanding of fast ice dynamics and their spatial extent.

While G/G-FO data span two decades, estimates of Earth’s oblateness from other satellite observations that date back to 1976 and provide a much longer data record – albeit at much coarser spatial resolution. This half-century long timeseries provides important constraints on ice mass change prior to the launch of GRACE in 2002. The data suggest that ice mass loss had already begun to accelerate by the 1990s. Recent progress in Earth system models, in conjunction with the long satellite data record, are being used to isolate trends in glacial isostatic adjustment (GIA) – which is the vertical movement of the Earth’s surface after the weight of glaciers is removed from them – and to improved estimates of ice mass loss prior to GRACE.

Solid Earth Sciences

Two presenters in this session described their efforts to evaluate signals in the G/G-FO data record associated with earthquakes. The G/G-FO data provide a unique opportunity to observe the Earth’s response to great earthquakes across diverse tectonic settings at time scales from days to decades. Using 13 earthquakes of magnitude (Mw)>8.0 over the last 20 years, it was found that elastic bulk modulus and viscosity govern large-scale coseismic and postseismic gravimetric changes, respectively. By constraining the solid Earth’s viscosity structure, improved physics-based models of long-term postseismic changes can be developed that incorporate observations from G/G-FO. The portion of the long-term gravity change signal that can be attributed to these earthquakes can then be removed from the G/G-FO data to better quantify processes related to ocean mass and hydrology changes. When physics-based models are not available, alternative statistic-based approaches can be used to remove the co- and post-seismic signature of large earthquakes (e.g., 2004 Andaman-Sumatra and 2011 Tohoku, Japan quakes) from the G/G-FO data. 

As the G/G-FO data record extends into its third decade, the long time series of Earth gravity changes requires careful consideration of the solid-Earth response to contemporary surface mass changes. To isolate the gravity signature of any surface mass signal, it is becoming evident that simple elastic loading corrections are no longer sufficient. Recent advances in mantle rheology – describing and understanding the nature of Earth’s mantle – derived in mineral laboratory experiments, tidal modeling, and seismic imaging provide unequivocal evidence of anelastic contributions to solid-Earth deformation on time-scales ranging from hours to decades. New developments in the solid-Earth capabilities of JPL’s Ice-sheet and Sea-level System Model (ISSM) in the form of viscoelastic solvers for Love numbers and sea-level change was used to implement and explore the so-called Extended Burgers Material (EBM) and so resulting viscoelastic deformations between the seismic and GIA time scales. Preliminary testing with EBM rheology shows potential for a ~15–20% increase in mass change trends for some regions.

A subdecadal variation of large-scale (i.e., spanning over continental scales) gravity signals with a period of approximately six years has attracted intense interest in the geodesy and geodynamic communities. Earth’s fluid core motions, magnetic field, Earth rotation, and crustal deformations have been invoked as causes for this signal. An analysis of G/G-FO data showed that a significant part of the approximately six-year signals is in fact due to climate-related oscillation of ocean-atmosphere coupling in the Pacific and Atlantic and variations in the land water storage over Africa.

Oceanography

In the oceanography session, five presenters reported on the combination of G/G-FO, satellite altimeters (e.g., from the joint NASA–European Sentinel-6 Michael Freilich mission), and in situ ocean floats (e.g., Argo) to investigate variations in sea level and ocean circulations – e.g., see Figure 1. Other presenters discussed improvements in data processing by reducing errors in atmospheric tides that could lead to spurious trends or double-counting a subset of ocean tides and by incorporating new dedicated ocean data grids that remove geodetic signals not related to ocean dynamics (e.g., global ocean mass; large earthquake signals).

GRACE figure 1
Figure 1. The top row of maps show estimates of individual components of the observed sea level trend in the northwestern Pacific from 2003 to 2016 including contributions from: land ice melt [top row, left], non-ice land water storage [top row, middle], and stereodynamic effects [top row right], which are estimated by directly combining in situ-based steric sea level (i.e., based on Argo ocean profiling floats) with the GRACE-derived ocean mass changes. The bottom row shows the sum of all of the components of sea level trend on the top two rows [bottom row, left], compared the same measurement using satellite-altimetry [bottom row, right]. These data clearly show the strong earthquake-related signature of ocean mass change east of Japan.
Image credit: Felix Landerer/updated from a similar figure published in Nature’s Communications Earth & Environment.

Another presenter described how ocean mass redistribution and regional sea-level rise in the North-West Pacific marginal seas (i.e., around Japan and north of the Philippines) is impacted by seafloor deformation from earthquakes, which alter the ocean bathymetry. G/G-FO data are key to isolating these deformation effects, which in turn allows better sea level projections that can be used for planning purposes.

While long-term sea level trends are of major concern, the seasonal cycle is the dominating climate signal in ocean bottom pressure variability. Accurate representation of seasonal cycle is thus key to efforts to improve observations and models of ocean bottom pressure. Examining differences between models and observations elucidates remaining uncertainty in observations and missing physics in the models (e.g., lack of intrinsic variability due to coarse resolution, no accounting of gravitational and loading effects). This allows researchers to advance the quality of ocean mass change observations and unravel underlying dynamics.

Lastly, ocean bottom pressure observations from G/G-FO have been used to monitor transport variability of deep currents associated overturning circulation in the Northern Hemisphere (the Labrador Current) and Southern Hemisphere (Weddell Sea Bottom Water). This deepwater transport provides an important pathway for the sequestration of excess atmospheric heat and carbon from locations of water mass formation. Continuous observations of deep ocean currents provide valuable insight into Earth’s climate system. However, harsh conditions and complex recirculation transport pathways make in-situ observations of these deep flowing currents challenging.

Interdisciplinary Science

Six presenters contributed to this session. The first study revisited geodetic assumptions about measuring so-called Earth Center-of-Mass (CM) motions that can be traced to planetary-scale seasonal and long-term variations of water cycling between the land the oceans. Differences in SLR and G/G-FO estimates of CM estimates can be helpful to refining global circulation models. In a related study, G/G-FO and SLR data have been used to pin down the causes and origin of polar motion, particularly the mass component related to gravity changes. A novel hybrid SLR/GRACE time-variable gravity approach closely aligned well with the hydrological excitation in independently polar motion.

Errors in GIA corrections impact altimeter estimates of sea level and ocean mass estimates and the so-called sea level budget. Choices in modeling GIA, particularly based on paleoshoreline sites, affect Earth’s viscosity structure and GIA response, influencing global mean sea level (GMSL) budget closure. Even minor Earth model changes can have notable effects on the alignment of GMSL (altimetry), ocean mass (GRACE), and steric sea level change (Argo). Thus, future research needs to focus on accounting for the complex three-dimensional structure of the solid Earth to improve GIA corrections and more accurately isolate contemporary mass change in the G/G-FO data record.

Despite GIA uncertainties, G/G-FO, in combination with sea level measurements from altimetry, provide a unique capability to measure changes in ocean heat content. The ocean takes up nearly 90% of Earth’s current energy imbalance, signifying their important role in overall planetary heating. Two presenters reported consistent findings of ocean heat uptake rates of 0.9 W/m2 based on the indirect geodetic satellite measurements of sea level and ocean mass – a value that is entirely independent of other techniques and thus provides crucial validation – see Figure 2. In addition, the results indicated the overall heating rate over the last decade has increased, which means heat accumulation is accelerating.

GRACE figure 2
Figure 2. This graph shows different estimates of ocean heat uptake (OHU), measured with in-situ ocean floats (orange curve), from top-of-the-atmosphere radiance satellite measurements of Earth energy imbalance (EEi) (black curve), and from geodetic satellites, i.e., G/G-FO and altimeters (blue curve). The satellite measurements agree well and show an increasing energy imbalance over the last 20 years.
Image credit: Felix Landerer/originally in Geophysical Research Letters.

Summary

The hybrid 2023 G-FO STM brought together over 120 international participants and showcased a broad range of science results and applications that are supported and uniquely enabled by the satellite gravimetry-based mass change observations. The G-FO data now span nearly six years and continue to provide crucial insights into how Earth’s hydrosphere, including sea level, ocean currents, and water distribution over land, is changing. The G/G-FO data are extending important climate data records (e.g., the Greenland and Antarctic ice mass time-series, ocean mass sea level data, and TWS over land) into their third decade. The upcoming GRACE-C mission will build on and expand this mature data record, which is increasingly enabling important applications in support of water-related decision making and planning.

The G-FO project team remains focused on providing the mass-change data record at a level of performance consistent with that of GRACE. As the current Solar Cycle 25 increases towards its anticipated maximum in 2024, the team continues to improve the mission’s accelerometer data products in support of that goal. Corresponding data improvements in the monthly gravity and mass change products will be released early 2024.

The next G-FO STM will be held from October 8–10, 2024 in Potsdam, Germany, organized by GFZ. Check the GRACE website for specific details as the date gets closer.

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    • NASA
      Summary of the Joint NASA LCLUC–SARI Synthesis Meeting
      By NASA
      Explore This Section Earth Home Earth Observer Home Editor’s Corner Feature Articles Meeting Summaries News Science in the News Calendars In Memoriam More Archives 35 min read
      Summary of the Joint NASA LCLUC–SARI Synthesis Meeting
      Introduction
      The NASA Land-Cover and Land-Use Change (LCLUC) is an interdisciplinary scientific program within NASA’s Earth Science program that aims to develop the capability for periodic global inventories of land use and land cover from space. The program’s goal is to develop the mapping, monitoring and modeling capabilities necessary to simulate the processes taking place and evaluate the consequences of observed and predicted changes. The South/Southeast Asia Research Initiative (SARI) has a similar goal for South/Southeast Asia, as it seeks to develop innovative regional research, education, and capacity building programs involving state-of-the-art remote sensing, natural sciences, engineering, and social sciences to enrich land use/cover change (LUCC) science in South/Southeast Asia. Thus it makes sense for these two entities to periodically meet jointly to discuss their endeavors.
      The latest of these joint meetings took place January 1–February 2, 2024, in Hanoi, Vietnam. A total of 85 participants attended the three-day, in-person meeting—see Photo.  A total of 85 participants attended the three-day, in-person meeting. The attendees represented multiple international institutions, including NASA (Headquarters and Centers), the University of Maryland, College Park (UMD), other American academic institutions, the Vietnam National Space Center (VNSC, the event host), the Vietnam National University’s University of Engineering and Technology, and Ho Chi Minh University of Technology, the Japanese National Institute of Environmental Studies (NIES), Center for Environmental Sciences, and the University of Tokyo. In addition, several international programs participated, including GEO Global Agricultural Monitoring (GEOGLAM), the System for Analysis, Research and Training (START), Global Observation of Forest and Land-use Dynamics (GOFC–GOLD), and NASA Harvest.
      Photo. A group picture of the meeting participants on the first day of the 2024 LCLUC SARI meeting in Hanoi, Vietnam. Photo credit: Hotel staff (Hanoi Club Hotel, Hanoi, Vietnam) Meeting Overview
      The purpose of the 2024 NASA LCLUC–SARI Synthesis meeting was to discuss LUCC issues – with a particular focus on their impact on Southeast Asian countries. Presenters highlighted ongoing projects aimed to advance our understanding of the spatial extent, intensity, social consequences, and impacts on the environment in South/Southeast Asian countries. While presenters reported on specific science results, they also were intentional to review and synthesize work from other related projects going on in Southeast Asia. 
      Meeting Goal
      The meeting’s overarching goal was to create a comprehensive and holistic understanding of various LUCC issues by examining them from multiple angles, including: collating information; employing interdisciplinary approaches; integrating research; identifying key insights; and enhancing regional collaborations. The meeting sought to bring the investigators together to bridge gaps, promote collaborations, and advance knowledge regarding LUCC issues in the region. The meeting format also provided ample time between sessions for networking to promote coordination and collaboration among scientists and teams. 
      Meeting and Summary Format
      The meeting consisted of seven sessions that focused on various LUCC issues. The summary report that follows is organized by day and then by session. All presentations in Session I and II are summarized (i.e., with all speakers, affiliations, and appropriate titles identified). The keynote presentation(s) from Sessions III–VI are summarized similarly. The technical presentations in each of these sessions are presented as narrative summaries. Session VII consisted of topical discussions to close out the meeting and summaries of these discussions are included herein. Sessions III–VI also included panel discussions, but to keep the article length more manageable, summaries of these discussions have been omitted. Readers interested in learning more about the panel discussions or viewing any of these presentations in full can access the information on the Joint LCLUC–SARI Synthesis meeting website.
      DAY ONE
      The first day of the meeting included welcoming remarks from the U.S. Ambassador to Vietnam (Session I), program executives of LCLUC and SARI,  as well as from national space agencies in South and Southeast Asia (Session II), and other LCLUC-thematic/overview presentations (Session III).
      Session 1: Welcoming Remarks
      Garik Gutman [NASA Headquarters—LCLUC Program Manager], Vu Tuan [VNSC’s Vietnam Academy of Science and Technology (VAST)—Vice Director General], Chris Justice [University of Maryland, College Park (UMD)—LCLUC Program Scientist], Matsunaga Tsuneo [National Institute of Environmental Studies (NIES), Japan], and Krishna Vadrevu [NASA’s Marshall Space Flight Center—SARI Lead] delivered opening remarks that highlighted collaborations across air pollution, agriculture, forestry, urban development, and other LUCC research areas. While each of the speakers covered different topics, they emphasized common themes, including advancing new science algorithms, co-developing products, and fostering applications through capacity building and training.
      After the opening remarks, special guest Marc Knapper [U.S. Ambassador to Vietnam] gave a presentation in which he emphasized the value of collaborative research between U.S. and Vietnamese scientists to address environmental challenges – especially climate change and LUCC issues. He expressed appreciation to the meeting organizers for promoting these collaborations and highlighted the joint initiatives between NASA and the U.S. Agency for International Development (USAID) to monitor environmental health and climate change, develop policies to reduce emissions, and support adaptation in agriculture. The U.S.–Vietnam Comprehensive Strategic Partnership emphasizes the commitment to address climate challenges and advance bilateral research. He concluded by encouraging active participation from all attendees and stressed the need for ongoing international collaboration to develop effective LUCC policies.
      Session-II: Programmatic and Space Agency Presentations
      NOTE: Other than Ambassador Knapper, the presenters in Session I gave welcoming remarks and programmatic and/or space agency presentations in Session II,.
      Garik Gutman began the second session by presenting an overview of the LCLUC program, which aims to enhance understanding of LUCC dynamics and environmental implications by integrating diverse data sources (i.e., satellite remote sensing) with socioeconomic and ecological datasets for a comprehensive view of land-use change drivers and consequences. Over the past 25 years, LCLUC has funded over 325 projects involving more than 800 researchers, resulting in over 1500 publications. The program’s focus balances project distribution that spans detection and monitoring, and impacts and consequences, including drivers, modeling, and synthesis. Gutman highlighted examples of population growth and urban expansion in Southeast Asia, resulting in environmental and socio-economic impacts. Urbanization accelerates deforestation, shifts farming practices to higher-value crops, and contributes to the loss of wetlands. This transformation alters the carbon cycle, degrades air quality, and increases flooding risks due to reduced rainwater absorption. Multi-source remote sensing data and social dimensions are essential in addressing LUCC issues, and the program aims to foster international collaborations and capacity building in land-change science through partnerships and training initiatives. (To learn more about the recent activities of the LCLUC Science Team, see Summary of the 2024 Land Cover Land Use Change Science Team Meeting.)
      Krishna Vadrevu explained how SARI connects regional and national projects with researchers from the U.S. and local institutions to advance LUCC mapping, monitoring, and impact assessments through shared methodologies and data. The initiative has spurred extensive activities, including meetings, training sessions, publications, collaborations, and fieldwork. To date, the LCLUC program has funded 35 SARI projects and helped build collaborations with space agencies, universities, and decision-makers worldwide. SARI Principal Investigators have documented notable land-cover and land-use transformations, observing shifts in land conversion practices across Asia. For example, the transition from traditional slash-and-burn practices for subsistence agriculture to industrial oil palm and rubber plantations in Southeast Asia. Rapid urbanization has also reshaped several South and Southeast Asian regions, expanding both horizontally in rural areas and vertically in urban centers. The current SARI solicitation funds three projects across Asia, integrating the latest remote sensing data and methods to map, monitor, and assess LUCC drivers and impacts to support policy-making.
      Vu Tuan provided a comprehensive overview of Vietnam’s advances in satellite technology and Earth observation capabilities, particularly through the LOTUSat-1 satellite (name derived from the “Lotus” flower), which is equipped with an advanced X-band Synthetic Aperture Radar (SAR) sensor capable of providing high-resolution imagery [ranging from 1–16 m (3–52 ft)]. This satellite is integral to Vietnam’s efforts to enhance disaster management and climate change mitigation, as well as to support a range of applications in topography, agriculture, forestry, and water management, as well as in oceanography and environmental monitoring. The VNSC’s efforts are part of a broader strategy to build national expertise and self-reliance in satellite technology, such as developing a range of small satellites (e.g., NanoDragon, PicoDragon, and MicroDragon) that progress in size and capability. Alongside satellite development, the VNSC has established key infrastructure, facilities, and capacity building in Hanoi, Nha Trang, and Ho Chi Minh City to support satellite assembly, integration, testing, and operation. Tuan showcased the application of remotely sensed LUCC data to map and monitor urban expansion in Ha Long city from 2000–2023 and the policies needed to manage these changes sustainably – see Figure 1.
      Figure 1. Urban expansion area in Ha Long City, Vietnam from 2000–2023 from multidate Landsat satellite imagery. Figure credit: Vu Tuan [VNSC] Tsuneo Matsunaga provided a detailed overview of Japan’s Greenhouse Gases Observing Satellite (GOSAT) series of satellites, data from which provide valuable insights into global greenhouse gas (GHG) trends and support international climate agreements, including the Paris Agreement.
      Matsunaga reviewed the first two satellites in the series: GOSAT and GOSAT-2, then previewed the next satellite in the series: GOSAT-GW, which is scheduled to launch in 2025. GOSAT-GW will fly the Total Anthropogenic and Natural Emissions Mapping Observatory–3 (TANSO-3) – an improved version of TANSO-2, which flies on GOSAT-2. TANSO-3 includes a Fourier Transform Spectrometer (FTS-3) that has improved spatial resolution [10.5 km (6.5 mi)] over TANSO-FTS-2 and precision that matches or exceeds that of its predecessor. TANSO-FTS-3 will allow estimates with precision better than 1 ppm for carbon dioxide (CO2) and 10 ppb for methane (CH4), as well as enabling nitrogen dioxide (NO2) measurements. GOSAT–GW will also fly the Advanced Microwave Scanning Radiometer (AMSR3) that will monitor water cycle components (e.g., precipitation, soil moisture) and ocean surface winds. AMSR3 builds on the heritage of three previous AMSR instruments that have flown on NASA and Japan Aerospace Exploration Agency (JAXA) missions.
      Matsunaga also highlighted the importance of ground-based validation networks, such as the Total Carbon Column Observing Network, COllaborative Carbon Column Observing Network, and the Pandora Global Network, to ensure satellite data accuracy.
      Son Nghiem [NASA/Jet Propulsion Laboratory (JPL)] addressed dynamic LUCC in Cambodia, Laos, Thailand, Vietnam, and Malaysia. The synthesis study examined the factors that evolve along the rural–urban continuum (RUC). Nghiem showcased this effort using Synthetic Aperture Radar (SAR) data from the Copernicus Sentinel-1 mission to map a typical RUC in Bac Lieu, Vietnam – see Figure 2.
      Figure 2. Land cover map of Bae Lieu, Vietnam, and surrounding rural areas. The image shows persistent building structures (red), agricultural areas (light green), aquacultural (light blue), tree cover (dark green), and water bodies (dark blue). Land-use classes used on this map are derived from Sentinel-1 Synthetic Aperture Radar (SAR) for the rural urban continuum around Bac Lieu. Figure credit: Son Nghiem [JPL] Nghiem described the study, which examined the role of rapid urbanization, agricultural conversion, climate change, and environment–human feedback processes in causing non-stationary and unpredictable impacts. This work illustrates how traditional trend analysis is insufficient for future planning. The study also examined whether slower or more gradual changes could inform policy development. To test these hypotheses, his research will integrate high-resolution radar and hyperspectral data with socioeconomic analyses. The study highlights the need for policies that are flexible and responsive to the unique challenges of different areas, particularly in “hot-spot” regions experiencing rapid changes.
      Peilei Fan [Tufts University] presented a study that synthesizes the complex patterns of LUCC, identifying both the spatial and temporal dynamics that characterize transitions in urban systems. The study explores key drivers, including economic development, population growth, urbanization, agricultural expansion, and policy shifts. She emphasized the importance of understanding these drivers for sustainable land management and urban planning. For example, the Yangon region of Myanmar has undergone rapid urbanization – see Figure 3. Her work reveals the need for integrated approaches that consider both urban and rural perspectives to manage land resources effectively and mitigate negative environmental and social impacts. Through a combination of case studies, statistical analysis, and policy review, Fan and her team aim to provide a nuanced understanding of the interactions between human activities and environmental changes occurring in the rapidly transforming landscapes of Southeast Asia.
      Figure 3. Landsat data can be used to track land cover change over time. For example, Thematic Mapper data have been used to track urban expansion around Yangon, Myanmar. The data show that the built-up area expanded from 161 km2 (62 mi2) in 1990 to 739 km2 (285 mi2) in 2020. Figure credit: Peleli Fan [Tufts University] Session III: Land Cover/Land Use Change Studies
      Tanapat Tanaratkaittikul [Geo-Informatics and Space Technology Development Agency (GISTDA), Thailand] highlighted GISTDA activities, which play a crucial role in advancing Thailand’s technological capabilities and addressing both national and global challenges, including Thailand Earth Observation System (THEOS) and its successors: THEOS-2 and THEOS-2A. THEOS-1, which launched in 2008, provides 2-m (6-ft) panchromatic and 15-m (45-ft) multispectral resolution with a 26-day revisit cycle, which can be reduced to 3 days with off-nadir pointing. Launched in 2023, THEOS-2 includes two satellites – THEOS-2A [a very high-resolution satellite with 0.5-m (1.5-ft) panchromatic and 2-m (6-ft) multispectral imagery] and THEOS-2B [a high-resolution satellite with 4-m (12-ft) multispectral resolution] – with a five-day revisit cycle. GISTDA also develops geospatial applications for drought assessment, flood prediction, and carbon credit calculations to support government decision-making and climate initiatives. GISTDA partners with international collaborators on regional projects, such as the Lancang-Mekong Cooperation Special Fund Project.
      Eric Vermote [NASA’s Goddard Space Flight Center] presented a keynote that focused on atmospheric correction of land remote sensing data and related algorithm updates. He highlighted the necessity of correcting surface imaging for atmospheric effects, such as molecular scattering, aerosol scattering, and gaseous absorption, which can significantly distort the satellite spectral signals and lead to potential errors in applications, such as land cover mapping, vegetation monitoring, and climate change studies.
      Vermote explained that the surface reflectance algorithm uses precise vector radiative transfer modeling to improve accuracy by incorporating atmospheric parameter inversion. It also adjusts for various atmospheric conditions and aerosol types – enhancing corrections across regions and seasons. He explained that SkyCam – a network of ground-based cameras – provides real-time assessments of cloud cover that can be used to validate cloud masks, while the Cloud and Aerosol Measurement System (CAMSIS) offers additional ground validation by measuring atmospheric conditions. He said that together, SkyCam and CAMSIS improve satellite-derived cloud masks, supporting more accurate climate models and environmental monitoring. Vermote’s work highlights the ongoing advancement of atmospheric correction methods in remote sensing.
      Other presentations in this session included one in which the speaker described how Yangon, the capital city in Myanmar, is undergoing rapid urbanization and industrial growth. From 1990–2020, the urban area expanded by over 225% – largely at the expense of agricultural and green lands. Twenty-nine industrial zones cover about 10.92% of the city, which have attracted significant foreign direct investment, particularly in labor-intensive sectors. This growth has led to challenges with land confiscations, inadequate infrastructure, and environmental issues (e.g., air pollution). Additionally, rural migration for employment has resulted in informal settlements, emphasizing the need for comprehensive urban planning that balances economic development with social equity and sustainability.
      Another presentation highlighted varying LUCC trends across Vietnam. In the Northern and Central Coastal Uplands, for example, swidden systems are shifting toward permanent tree crops, such as rubber and coffee. Meanwhile, the Red River Delta is seeing urban densification and consolidation of farmland – transitioning from rice to mixed farming with increased fruit and flower production. Similarly, the Central Coastal Lowlands and Southeastern regions are experiencing urban growth and a shift from coastal agriculture – in this case, to shrimp farming – leading to mangrove loss. The Central Highlands is moving from swidden to tree crops, particularly fruit trees, while the Mekong River Delta is increasing rice cropping and aquaculture. These changes contribute to urbanization, altered farming practices, and biodiversity loss. Advanced algorithms (e.g., the Time-Feature Convolutional Neural Network model) are being used to effectively map these varied LUCC changes in Vietnam.
      Another presenter explained how 10-m (33-ft) resolution spatially gridded population datasets are essential to address LUCC in environmental and socio-demographic research. There was also a demonstration of PopGrid, which is a collaborative initiative that provides access to various global-gridded population databases, which are valuable for regional LUCC studies and can support informed decision-making and policy development.
      DAY TWO
      The second day’s presentations centered around urban LUCC (Session IV) as well as interconnections between agriculture and water resources. (Session V).
      Session IV: Urban Land Cover/Land Use Change
      Gay Perez [Philippines Remote Sensing Agency (PhilSA)] presented a keynote focused on PhilSA’s mission to advance Philippines as a space-capable country by developing indigenous satellite and launch technologies. He explained that PhilSA provides satellite data in various categories, including sovereign, commercial, open-access, and disaster-activated. He noted that the ground infrastructure – which includes three stations and a new facility in Quezon – supports efficient data processing. For example, Perez stated that in 2023, PhilSA produced over 10,000 maps for disaster relief, agricultural assessments, and conservation planning.
      Perez reviewed PhilSA’s Diwata-2 mission, which launched in 2018 and operates in a Sun-synchronous orbit around 620 km (385 mi) above Earth. With a 10-day revisit capability, it features a high-precision telescope [4.7 m (15ft) resolution], a multispectral imager with four bands, an enhanced resolution camera, and a wide-field camera. Since launch, Diwata-2 has captured over 100,000 global images, covering 95% of the Philippines. Looking to the near future, Perez reported that PhilSA’s launch of the Multispectral Unit for Land Assessment (MULA) satellite is planned for 2025. He explained that MULA will capture images with a 5-m (~16-ft) resolution and 10–20-day revisit time, featuring 10 spectral bands for vegetation, water, and urban analysis.
      Perez also described the Drought and Crop Assessment and Forecasting project, which addresses drought risks and mapping ground motion in areas, e.g., Baguio City and Pangasinan. Through partnerships in the Pan-Asia Partnership for Geospatial Air Pollution Information (PAPGAPI) and the Pandora Asia Network, PhilSA monitors air quality across key locations, tracking urban pollution and cross-border particulate transport. PhilSA continues to strengthen Southeast Asian partnerships to drive sustainable development in the region.
      Jiquan Chen [Michigan State University] presented the second keynote address, which focused on the Urban Rural Continuum (URC). Chen emphasized the importance of synthesizing studies that explore factors such as population dynamics, living standards, and economic development in the URC. Key considerations include differentiating between two- and three-dimensional infrastructures and understanding constraints from historical contexts. Chen highlighted critical variables from his analysis including net primary productivity, household income, and essential infrastructure elements, such as transportation and healthcare systems. He advocated for integrated models that combine mechanistic and empirical approaches to grasp the dynamics of URC changes, stressing their implications for urban planning, environmental sustainability, and social equity. He concluded with a call for collaboration to enhance these models and tackle challenges arising from the changing urban–rural landscape.
      Tep Makathy [Cambodian Institute For Urban Studies] discussed urbanization in Phnom Penh, Cambodia. He explained that significant LUCC and infrastructure developments have been fueled by direct foreign investment; however, this development has resulted in environmental degradation, urban flooding, and infrastructure strain. Tackling pollution, congestion, preservation of green spaces, and preserving the historical heritage of the city will require sustainable urban planning efforts.
      Nguyen Thi Thuy Hang [Vietnam Japan University, Vietnam National University, Hanoi] explained how flooding poses a significant annual threat to infrastructure and livelihoods in Can Tho, Vietnam. Therefore, it is essential to incorporate climate change considerations into land-use planning by enhancing the accuracy of vegetation layer classifications. Doing so will improve the representation of land-cover dynamics in models that decision-makers use when planning urban development. In addition, Hang reported that a more comprehensive survey of dyke systems will improve flood protection and identify areas needing reinforcement or redesign. These studies could also explore salinity intrusion in coastal agricultural areas that could impact crop yields and endanger food security.
      In this session, two presenters highlighted how SAR data, which uses high backscatter to enhance the radar signal, is being used to assist with mapping urban areas in their respective countries. The phase stability and orientation of building structures across SAR images aid in consistent monitoring and backscatter, producing distinct image textures specific to urban settings. Researchers can use this heterogeneity and texture to map urban footprints, enabling automated discrimination between urban and non-urban areas. The first presenters showed how Interferometric Synthetic Aperture Radar techniques, such as Small Baseline Subset (SBAS) and Persistent Scatterer (PS) have been highly effective for mapping and monitoring land subsidence in coastal and urban areas in Vietnam. This approach has been applied to areas along the Saigon River as well as in Ho Chi Minh, Vietnam. The second presenter described an approach (using SAR data with multitemporal coherence and the K-means classification method) that has been used effectively to study urban growth in the Denpasar Greater Area of Indonesia between 2016 and 2022. The technique identified the conversion of 4376 km2 (1690 mi2) of rural to built-up areas, averaging 72.9 hectares (0.3 mi2) per year. Urban sprawl was predominantly observed in the North Kuta District, where the shift from agricultural to built-up land use has been accompanied by severe traffic congestion and other environmental issues.
      Another presenter showed how data from the QuikSCAT instrument, which flew on the Quick Scatterometer satellite, and from the Sentinel-1 C-band SAR can be combined to measure and analyze urban built-up volume, specifically focusing on the vertical growth of buildings across various cities. By integrating these datasets, researchers can assess urban expansion, monitor the development of high-rise buildings, and evaluate the impact of urbanization on infrastructure and land use. This information is essential for urban planning, helping city planners and policymakers make informed decisions to accommodate growing populations and enhance sustainable urban development.
      Session V – LUCC, Agriculture, and Water Resources
      Chris Justice presented the keynote for this session, in which he addressed the GEOGLAM initiative and the NASA Harvest program. GEOGLAM, initiated by the G20 Agriculture Ministers in 2011, focuses on agriculture and food security to increase market transparency and improve food security. These efforts leverage satellite-based Earth observations to produce and disseminate timely, relevant, and actionable information about agricultural conditions at national, regional, and global scales to support agricultural markets and provide early warnings for proactive responses to emerging food emergencies. NASA Harvest uses satellite Earth observations to benefit global food security, sustainability, and agriculture for disaster response, climate risk assessments, and policy support. Justice also emphasized the use of open science and open data principles, promoting the integration of Earth observation data into national and international agricultural monitoring systems. He also discussed the development and application of essential agricultural variables, in situ data requirements, and the need for comprehensive and accurate satellite data products.
      During this session, another presentation focused on how VNSC is engaged in several agricultural projects, including mapping rice crops, estimating yields, and assessing environmental impacts. VNSC has created high-accuracy rice maps for different seasons that the Vietnamese government uses to monitor and manage agricultural production. Current initiatives involve using satellite data to estimate CH4 emissions from rice paddies, biomass mapping, and monitoring rice straw burning. For example, in the Mekong Delta, numerous environmental factors, including climate change-induced stress (e.g., sea-level rise), flooding, drought, land subsidence, and saltwater intrusion, along with human activities like dam construction, sand mining, and groundwater extraction, threaten the sustainability of rice farming and farmer livelihoods. To address these challenges, sustainable agricultural practices are essential to improving rice quality, diversify farming systems, adopt low-carbon techniques, and enhance water management.
      Presentations highlighted the importance of both optical and SAR data for LUCC studies, particularly in mapping agricultural areas. A study using Landsat time-series data demonstrated its value in monitoring agricultural LUCC in Houa Phan Province, Laos, and Son La Province, Vietnam. Land cover types were classified through spectral pattern analysis, identifying distinct classes based on Landsat reflectance values. The findings revealed significant natural forest loss alongside increases in cropland and forest plantations due to agricultural expansion. High-resolution imagery validated these results, indicating the scalability of this approach for broader regional and global land-cover monitoring. Another study showcased the effectiveness of SAR data from the Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) on the Japanese Advanced Land Observing Satellite-2 (ALOS-2) for mapping and monitoring agricultural land use in Suphanburi, Thailand. This data proved particularly useful for capturing seasonal variations and diverse agricultural practices. Supervised machine learning methods, such as Random Forest classifiers, combined with innovative spatial averaging techniques, achieved high accuracy in distinguishing various agricultural conditions.
      In the session, presenters also discussed the use of Sentinel-1 SAR data for mapping submerged and non-submerged paddy soils was highlighted, demonstrating its effectiveness in understanding water management issues see – Figure 4. Additionally, large-scale remote sensing data and cloud computing were shown to provide unprecedented opportunities for tracking agricultural land-use changes in greater detail. Case studies from India and China illustrated key challenges, such as groundwater depletion in irrigated agriculture across the Indo-Ganges region and the impacts on food, water, and air quality in both countries.
      Figure 4. Series of Sentinel-1 radar data images showing submerged paddy soil (blue) and non-submerged paddy soil (red) in the Mekong Delta, Vietnam. Figure credit: Hiranori Arai [International Rice Research Institute] The session also focused on Water–Energy–Food (WEF) issues related to the Mekong River Basin’s extensive network of hydroelectric dams, which present both benefits and challenges. While these dams support sectors such as irrigated agriculture and hydropower, they also disrupt vital ecosystem services, including fish habitats and biodiversity. Collaborative studies integrating satellite and ground data, hydrological models, and socio-economic frameworks highlight the need to balance these benefits with ecological and social costs. Achieving sustainable management requires cross-sectoral and cross-border cooperation, as well as the incorporation of traditional knowledge to address WEF trade-offs and governance challenges in the region.
      DAY THREE
      The third day included a session that explored the impacts of fire, GHG emissions, and pollution (Session VI) as well as a summary discussion on synthesis (Session VII).
      Session VI: Fires, Greenhouse Gas Emissions, and Pollution
      Chris Elvidge [Colorado School of Mines] presented a keynote on the capabilities and applications of the Visible Infrared Imaging Radiometer Suite (VIIRS) Nightfire [VNF] system, an advanced satellite-based tool developed by the Earth Observation Group. VIIRS Nightfire uses four near- and short-wave infrared channels, initially designed for daytime imaging, to detect and monitor infrared emissions at night. The system identifies various combustion sources, including both flaming and non-flaming activities (e.g., biomass burning, gas flaring, and industrial processes). It calculates the temperature, source area, and radiant heat of detected infrared emitters using physical laws to enable precise monitoring of combustion events and provide insight into exothermic and endothermic processes.
      Elvidge explained that VNF has been vital for near-real-time data in Southeast Asia. The system has been used to issue daily alerts for Vietnam, Thailand, and Indonesia. Recent updates in Version 4 (V4) include atmospheric corrections and testing for secondary emitters with algorithmic improvements – with a 50% success rate in identifying additional heat sources. The Earth Observation Group maintains a multiyear catalog of over 20,000 industrial infrared emitters available through the Global Infrared Emitter Explorer (GIREE) web-map service. With VIIRS sensors expected to operate until about 2040 on the Joint Polar Satellite System (JPSS) platforms, this system ensures long-term, robust monitoring and analysis of global combustion events, proving essential for tracking the environmental impacts of industrial activities and natural combustion processes on the atmosphere and ecosystems.
      Toshimasa Ohara [Center for Environmental Science, Japan—Research Director] continued with the second keynote and provided an in-depth analysis of long-term trends in anthropogenic emissions across Asia. The regional mission inventory in Asia encompasses a range of pollutants and offers detailed emissions data from 1950–2020 at high spatial and temporal resolutions. The study employs both bottom-up and top-down approaches for estimating emissions, integrating satellite observations to validate data and address uncertainties. Notably, emissions from China, India, and Japan have shown signs of stabilization or reduction, attributed to stricter emission control policies and technological advancements. Ohara also highlighted Japan’s effective air pollution measures and the importance of extensive observational data in corroborating emission trends. His presentation emphasized the need for improved methodologies in emission inventory development and validation across Asia, aiming to enhance policymaking and environmental management in rapidly industrializing regions.
      Several presenters during this session focused on innovative approaches to understand and mitigate GHG emissions and air pollution. One presenter showed how NO2 data from the TROPOspheric Monitoring Instrument (TROPOMI) on the European Sentinel-5 Precursor have been validated against ground-based observations from Pandora stations in Japan, highlighting the influence of atmospheric conditions on measurement accuracy. Another presenter described an innovative system that GISTDA used to combine satellite remote sensing data with Artificial Intelligence (AI). This system was used to monitor and analyze the concentration of fine particulate matter (PM) in the atmosphere in Thailand. (In this context fine is defined as particles with diameters ≤ 2.5 µm, or PM2.5.) These applications, which are accessible through online, cloud-based platforms and mobile applications for iOS and Android devices, allow users, including citizens, government officers, and policymakers, to access PM2.5 data in real-time through web and mobile interfaces.
      A project under the United Nations Economic and Social Commission for Asia and the Pacific in Thailand is focused on improving air quality monitoring across the Asia–Pacific region by integrating satellite and ground-based data. At the core of this effort, the Pandora Asia Network, which includes 30 ground-based instruments measuring pollutants such as NO₂ and sulfur dioxide (SO₂), is complemented by high-resolution observations from the Geostationary Environment Monitoring Spectrometer (GEMS) aboard South Korea’s GEO-KOMPSAT-2B (GK-2B) satellite. The initiative also provides training sessions to strengthen regional expertise in remote sensing technologies for air quality management and develops decision support systems for evidence-based policymaking, particularly for monitoring pollution sources and transboundary effects like volcanic eruptions. Future plans include expanding the Pandora network and enhancing data integration to support local environmental management practices.
      PM2.5 levels in Vietnam are influenced by both local emissions and long-range pollutant transport, particularly in urban areas.The Vietnam University of Engineering and Technology, in conjunction with VNSC, continues to map and monitor PM2.5 using satellites and machine learning while addressing data quality issues that stem from missing satellite data and limited ground monitoring stations – see Figure 5.
      In addition to mapping and monitoring pollutants, another presentater explained that significant research is underway to address their health impacts. In Hanoi, exposure to pollutants ( e.g., PM2.5, PM10, and NO2) has led to increased rates of respiratory diseases (e.g., pneumonia, bronchitis, and asthma) among children,  as well as elevated instances of cardiovascular diseases among adults. A substantial mortality burden is attributable to fine particulate matter – particularly in densely populated areas like Hanoi. Compliance with stricter air quality guidelines could potentially prevent thousands of premature deaths. For example, preventive measures enacted during the COVID-19 pandemic resulted in reduced pollution levels that were associated with a decrease in avoidable mortality rates. In response to these challenges, Vietnam has implemented air quality management policies, including national technical regulations and action plans aimed at controlling emissions and enhancing monitoring; however, current national standards still fall short of the more stringent guidelines recommended by the World Health Organization. Improved air quality standards and effective policy interventions are needed to mitigate the health risks associated with air pollution in Vietnam.
      Figure 5. Map of particulate matter (PM 2.5) variations observed across Vietnam, using multisatellite aerosol optical depth (AOD) data from the Moderate Resolution Imaging Spectrogradiometer (MODIS) on NASA’s Aqua and Terra platforms, and from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the NASA–NOAA Suomi NPP platform, combined with ground-based AOD and meteorological data. Figure credit: Thanh Nguyen [Vietnam National University of Engineering and Technology, Vietnam] Another presenter explained how food production in Southeast Asia contributes about 40% of the region’s total GHG emissions – with rice and beef production identified as the largest contributors for plant-based and animal-based emissions, respectively. Another presentation focused on a study that examined GHG emissions from agricultural activities, which suggests that animal-based food production – particularly beef – generates substantially higher GHG emissions per kg of food produced compared to plant-based foods, such as wheat and rice. Beef has an emission intensity of about 69 kg of CO2 equivalent-per-kg, compared to 2 to 3 kg of CO2 equivalent-per-kg for plant-based foods. The study points to mitigation strategies (e.g., changing dietary patterns, improving agricultural practices) and adopting sustainable land management. Participants agreed that a comprehensive policy framework is needed to address the environmental impacts of food production and reduce GHG emissions in the agricultural sector.
      In another presentation, the speaker highlighted the fact that Southeast Asian countries need an advanced monitoring, reporting, and verification system to track GHG emissions – particularly within high-carbon reservoirs like rice paddies. To achieve this, cutting-edge technologies (e.g., satellite remote sensing, low-cost unmanned aerial vehicles, and Internet of Things devices) can be beneficial in creating sophisticated digital twin technology for sustainable rice production and GHG mitigation.
      Another presentation featured a discussion about pollution resulting from forest and peatland fires in Indonesia, which is significantly impacting air quality. Indonesia’s tropical peatlands – among the world’s largest and most diverse – face significant threats from frequent fires. Repeated burning has transformed forests into shrubs and secondary vegetation regions, with fires particularly affecting forest edges and contributing to a further retreat of intact forest areas. High-resolution data is essential to map and monitor changes in forest cover, including pollution impacts.
      Another speaker described a web-based Geographic Information Systems (GIS) application that has been developed to support carbon offsetting efforts in Laos – to address significant environmental challenges, e.g., deforestation and climate change. Advanced technologies (e.g., remote sensing, GIS, and Global Navigation Satellite Systems) are used to monitor land-use changes, carbon sequestration, and ecosystem health. By integrating various spatial datasets, the web GIS app enhances data collection precision, streamlines monitoring processes, and provides real-time information to stakeholders for informed decision-making. This initiative fosters collaboration among local communities, government agencies, and international partners, while emphasizing the importance of government support and international partnerships. Ultimately, the web GIS application represents a significant advancement in Laos’s commitment to environmental sustainability, economic growth, and the creation of a greener future.
      Session VII. Discussion Session on Synthesis
      The meeting concluded with a comprehensive discussion on synthesizing themes related to LUCC. The session focused on three themes: LUCC, agriculture, and air pollution. The session focused on trends and projections as well as the resulting impacts in the coming years. It also highlighted research related to these topics to inform more sustainable land use policies. A panel of experts from different Southeast Asian countries addressed these topics. A summary of the key points shared by the panelists for each theme during the discussion is provided below.
      LUCC Discussions
      This discussion focused on the challenges of balancing economic development with environmental sustainability in Southeast Asian countries, e.g., mining in Myanmar, agriculture in Vietnam, and rising land prices in Thailand. More LUCC research is needed to inform decision-making and improve land-use planning during transitions from agriculture to industrialization while ensuring food security. The panelists also discussed urban sprawl and infrastructure development along main roads in several Southeast Asian countries, highlighting the social and environmental challenges arising from uncoordinated growth. It was noted that urban infrastructure lags behind population increases, resulting in traffic congestion, pollution, and social inequality. Cambodia, for example, has increased foreign investments, which presents similar dilemmas of economic growth accompanied by significant environmental degradation. Indonesia is another example of a Southeast Asian nation facing rapid urbanization and inadequate spatial planning, leading to flooding, groundwater depletion, and pollution. These issues further highlight the need for integrated satellite monitoring to inform land-use policies. Finally, recognizing the importance of public infrastructure in growth management, it was reported that the Thai government is already using technology to manage urban development alongside green spaces.
      Panelists agreed that LUCC research is critical for guiding policymakers toward sustainable land-use practices – emphasizing the necessity for improved communication between researchers and policymakers. While the integration of technologies (e.g., GIS and remote sensing) is beginning to influence policy decisions, room for improvement remains. In summary, the discussions stressed the importance of better planning, technology integration, and policy-informed research to reconcile economic growth with sustainability. Participants also highlighted the need to engage policymakers, non-government organizations, and the private sector in using scientific evidence for sustainable development. Capacity building in Laos, Cambodia, and Myanmar, where GIS and remote sensing technologies are still developing, is crucial. Community involvement is essential for translating research findings into actionable policies to address real-world challenges and social equity.
      Agriculture Discussions
      These discussions explored the intricate relationships between agricultural practices, economic growth, and environmental sustainability in Southeast Asia. As an example, despite national policies to manage the land transition in Vietnam, rapid conversions from forest to agricultural land and further to residential and industrial continue. While it is recognized that strict land management plans may hinder future adaptability, further regulation is needed. These rapid shifts in land use have increased land for economic development – especially in industrial and residential sectors – and contribute to environmental degradation, e.g., pollution and soil erosion. In Thailand, land is distributed among agriculture (50%), forest (30%), and urban (20%) areas. Despite a long history of agricultural practices, Vietnam faces new challenges from climate change and extreme weather.
      Thailand, meanwhile, is exploring carbon credits to incentivize sustainable farming practices – although this requires significant investment and time. The nation is well-equipped with a robust water supply system, and ongoing efforts to enhance crop yields on Vietnam’s Mekong Delta, salinity levels, and flooding intensity have increased as a result of the rise in incidents of extreme weather, prompting advancements in rice farming mechanization to be implemented that are modeled after practices that have been successfully used in the Philippines.
      Despite these advances, issues (e.g., over-application of rice seeds) remain. The dominant land cover type in Malaysia is tropical rainforest, although agriculture – particularly oil palm plantations – also plays a significant role in land use. While stable, it shares environmental concerns with Indonesia. The country is integrating solar energy initiatives, placing solar panels on former agricultural lands and recreational areas, which raises coastal environmental concerns. In Taiwan, substantial land use changes have stemmed from solar panel installations to support green energy goals but have led to increased temperatures and altered wind patterns.
      All panelists agreed that remote sensing technologies are vital to inform agricultural policy across the region. They emphasized the need to transition from academic research to actionable insights that directly inform policy. Panelists also discussed the challenge of securing funding for actionable research – underlining the importance of recognizing the transition required for research to inform operational use. Some countries (e.g., Thailand) have established operational crop monitoring systems, while others (e.g., Vietnam) primarily depend on research projects. Despite progress in Malaysia’s monitoring of oil palm plantations, a comprehensive operational monitoring system is still lacking in many areas. The participants concluded that increased efforts are needed to promote the wider adoption of remote sensing technologies for agricultural and environmental monitoring, with emphasis on developing operational systems that can be integrated into policy and decision-making processes.
      Air Pollution Discussions
      The discussion on air pollution focused on various sources in Southeast Asia, which included both local and transboundary factors. Panelists highlighted that motor vehicles, industrial activities, and power plants are major contributors to pollutants, such as PM2.5, NO2, ozone (O3), and carbon monoxide (CO). Forest fires in Indonesia – particularly from South Sumatra and Riau provinces – are significantly impacting neighboring countries, e.g., Malaysia. A study found that most PM2.5 pollution in Kuala Lumpur originates from Indonesia. During the COVID-19 pandemic, pollution levels dropped sharply due to reduced economic activity; however, data from 2018–2023 shows that PM2.5 levels have returned to pre-pandemic conditions.
      The Indonesian government is actively working to reduce deforestation and emissions, aiming for a 29% reduction by 2030. Indonesia is also participating in carbon markets and receiving international payments for emission reductions. Indonesia’s emissions also stem from energy production, industrial activities, and land-use changes, including peat fires. The Indonesian government reports anthropogenic sources – particularly from the energy sector and industrial activities, forest and peat fires, waste, and agriculture – continue to escalate. While Indonesia is addressing these issues, growing population and energy demands continue to drive pollution levels higher.
      Vietnam and Laos are facing similar challenges related to air pollution – particularly from agricultural residue burning. Both governments are working on expanding air quality monitoring, regulating waste burning, and developing policies to mitigate pollution. Vietnam has been developing provincial air quality management plans and expanding its monitoring network. Laos has seen increased awareness of pollution, accompanied by government measures aimed at restricting burning and improving waste management practices.
      The panelists agreed that collaborative efforts for regional cooperation are essential to address air pollution. This will require collaboration in research and data sharing to inform policy decisions. There is a growing interest in leveraging satellite technology and modeling approaches to enhance air quality forecasting and management. To ensure that research translates into effective policy, communication of scientific findings to policymakers is essential – particularly by clearly communicating complex research concepts in accessible formats. All panelists agreed on the importance of improving governance, transparency, and scientific communication to better translate research into policy actions, highlighting collaborations with international organizations – including NASA – to address air quality issues. While significant challenges related to air pollution persist in Southeast Asia, noteworthy efforts are underway to improve awareness, research, and collaborative governance aimed at enhancing air quality and reducing emissions.
      Conclusion
      The LCLUC–SARI Synthesis meeting fostered collaboration among researchers and provided valuable updates on recent developments in LUCC research, exchange of ideas, integration of new data products, and discussions on emerging science directions. This structured dialogue (particularly the discussions in each session) helped the attendees identify priorities and needs within the LUCC community. All panelists and meeting participants commended the SARI leadership for their proactive role in facilitating collaborations and discussions that promote capacity-building activities across the region. SARI activities have significantly contributed to enhancing the collective ability of countries in South and Southeast Asia to address pressing environmental challenges. The meeting participants emphasized the importance of maintaining and expanding these collaborative efforts, which are crucial for fostering partnerships among governments, research institutions, and local communities. They urged SARI to continue organizing workshops, training sessions, and knowledge-sharing platforms that can equip stakeholders with the necessary skills and resources to tackle environmental issues such as air pollution, deforestation, climate change, and sustainable land management.
      Krishna Vadrevu
      NASA’s Marshall Space Flight Center
      krishna.p.vadrevu@nasa.gov
      Vu Tuan
      Vietnam National Science Center, Vietnam
      vatuan@vnsc.org.vn
      Than Nguyen
      Vietnam National University Engineering and Technology, Vietnam
      thanhntn@vnu.edu.vn
      Son Nghiem
      Jet Propulsion Laboratory
      son.v.nghiem@jpl.nasa.gov
      Tsuneo Matsunaga
      National Institute of Environmental Studies, Japan
      matsunag@nies.go.jp
      Garik Gutman
      NASA Headquarters
      ggutman@nasa.gov
      Christopher Justice
      University of Maryland College Park
      cjustice@umd.edu
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      To the NASA Science Community – 
      As the nation’s leader in Earth and space science, NASA Science operates within the broader context of the federal government and its priorities. As part of the Executive Branch, we are always responsive to the direction set by the Administration, including executive orders and policy guidance that relate to our programs and activities. 
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      We appreciate your patience and dedication, and we will share more details as they become available. Thank you for your continued partnership in advancing NASA Science for the benefit of the nation. 
      -Nicky Fox
      Associate Administrator, NASA Science Mission Directorate 
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