A decade of radar insight into polar ice: what Copernicus Sentinel-1 brings
Ten years of continuous measurements by Copernicus Sentinel-1 satellites have delivered what glaciologists had been missing for years: a stable, comparable and sufficiently detailed “film”, rather than just a series of disconnected photographs, of how ice from Greenland and Antarctica moves toward the sea. It is precisely this ice flow – the speed at which glaciers and ice sheets “drain” from land into the ocean – that is crucial for understanding future sea-level rise and for validating climate models. In a scientific study published in
Remote Sensing of Environment, the authors showed that Sentinel-1 data enabled the first continuous, high-resolution record of ice velocities across entire ice sheets from 2014 to 2024. Such a series helps separate short-term seasonal fluctuations from long-term trends, and more precisely estimate how much ice is “delivered” to the sea through glacier dynamics.
The work relies on advanced processing of radar measurements and was published as part of a broader collection of scientific papers dedicated to the 10th anniversary of the Sentinel-1 mission. The very fact that it is a thematic collection underscores a message researchers have been repeating for years: without long, uniform data records, it is difficult to build reliable climate evidence. When measurements are interrupted or different sensors must be merged, the risk increases that a change in method will be misinterpreted as a change in nature. That is why a decade of Sentinel-1 measurements is increasingly treated as “core infrastructure” for climate analyses, as important as ocean observing networks or meteorological reanalyses. In polar regions, where field measurements are not always possible, satellites often remain the only systematic way to monitor large-scale areas.
Sentinel-1 satellites use C-band synthetic aperture radar (SAR), which means they “see” through clouds, smoke and the polar night. This is a particular advantage in areas where optical imaging is often limited by persistent cloud cover and a lack of light. SAR imagery enables frequent repeat observations, and from pairs of images it is possible to calculate how far the ice moved between two satellite passes. In practice, this opens the possibility of precisely tracking accelerations and slowdowns of flows, as well as changes associated with cracking, calving of icebergs or damage to floating ice shelves. In its overviews of Sentinel-1 applications, ESA highlights that the instrument has become a standard beyond science, from flood monitoring to maritime surveillance, but in the cryosphere its advantage is especially pronounced.
The first continuous record of ice velocities at the scale of entire continents
The key novelty in the published work is not only the length of the time series, but also the spatial precision and the systematic production. Operational annual ice-velocity maps, produced within the Copernicus Climate Change Service (C3S), are based on repeated Sentinel-1 acquisitions at intervals of six and 12 days. The products are delivered on a grid of about 250 meters for Greenland and 200 meters for Antarctica, with velocity components by direction, uncertainty estimates and the number of valid pixels in the calculation. The dataset description emphasizes that it is a European “state-of-the-art” product for ice velocities, intended for long-term climatological records. Such resolution makes it possible to detect both major ice streams and local hotspots of acceleration that would remain invisible on coarser maps.
The temporal coverage of the operational products is also important. For Greenland, an annual series is available in the Climate Data Store from 2014 onward, while for Antarctica the same operational dataset emphasizes availability from 2021 onward, with coverage limitations in peripheral areas where repeat acquisitions exist. The study, however, shows the broader potential of the archive and methodology: through advanced processing and use of the large radar archive, it is possible to build comparable maps for longer periods and analyze changes across the decade. This matters because ice-sheet dynamics often break precisely in the marginal zones, where interactions with the ocean and topography are strongest. In these zones changes can be rapid but also spatially very heterogeneous, so “dense” sampling from air or space is crucial for understanding the processes.
For science, it is crucial that this is a systematically produced product: the same sensor type, similar acquisition geometry and standardized processing procedures make it possible to assess trends not “by eye”, but to confirm them statistically. The study states that advanced processing chains were developed that combine two radar techniques – feature tracking (offset tracking) and interferometry (InSAR) – to obtain reliable velocities on both slower and faster parts of the ice sheets. The paper’s authors (Jan Wuite, Thomas Nagler, Markus Hetzenecker and Helmut Rott) emphasize that this approach reduces “gaps” in coverage and increases comparability over time, which is a prerequisite for long-term climate records. This is precisely where the difference between individual research campaigns and stable, operational data production becomes visible.
Antarctica: the coast as the zone of the fastest changes
Maps of Antarctica, derived as an average for 2014–2024, show that in coastal zones and along the main ice streams, speeds often range between about 1 and 15 meters per day, while the continent’s interior is significantly calmer. Regions of the Antarctic Peninsula, Alexander Island, and large areas of the West Antarctic and East Antarctic ice sheets are particularly highlighted, where ice is “channeled” toward the sea. Because of the orbital acquisition strategy, a large part of the coast was recorded at regular intervals of six or 12 days, which is a major change in polar research compared with earlier, more sparsely available series. Such frequency helps distinguish stable flows from those that show an accelerating trend. In the context of sea-level rise, coastal zones are critical because that is where most of the ice mass “discharge” into the ocean occurs.
Pine Island and neighboring glaciers: acceleration at the boundary of land and sea
One of the most monitored examples in West Antarctica is Pine Island Glacier, whose flow stands out clearly on velocity maps. The study reports that at its grounding line – the place where ice detaches from the bed and transitions into a floating ice shelf – a continuous increase in flow speed was recorded over the observed period, from about 10.6 to around 12.7 meters per day. The authors emphasize that nearby glaciers show similar acceleration signals, pointing to a broader regional process. Such changes are not just “numbers on a map”, but an indicator of the dynamics of a system sensitive to changes in the ocean and at the ice-sheet margin. The grounding line is particularly important because there the system transitions from a regime of friction against the bed to a regime of flotation, and that transition often determines the stability of the entire glacier flow. That is why Pine Island has for years been observed as one of the key indicators of the stability of the West Antarctic ice sheet.
The mechanism most commonly linked in the literature to accelerations on that side of Antarctica is thinning of floating ice shelves under the influence of warmer ocean water, accompanied by a retreat of the grounding line inland. When an ice shelf thins, the “buttressing” effect that otherwise slows the ice coming from land weakens. If at the same time the grounding line shifts onto deeper terrain, the system can become more sensitive to further changes, including chain reactions. In such circumstances, satellite-derived ice velocity becomes an early-warning tool: a change in dynamics can precede visible changes in the shape of the front or an increased frequency of major calving events. That is precisely why researchers emphasize the need to track ice velocities not sporadically, but as a continuous series, in combination with oceanographic and meteorological data wherever feasible.
Greenland: fast outlet glaciers and ice “highways”
In Greenland, the highest speeds do not occur in the center of the ice sheet, but at its margin, where outlet glaciers transport ice toward fjords and the open sea. The study presents average-speed views that in some places reach about 15 meters per day, with pronounced spatial differences depending on topography, temperature, precipitation and contact with the ocean. Zones along the west coast stand out in particular, where glaciers flow into relatively warm seawater and where changes can happen quickly, including shifts in the position of the front, calving frequency and seasonal accelerations. From the perspective of climate assessments, Greenland is important because it combines surface melting and dynamic acceleration of outlet glaciers. When these two processes combine, the total contribution to sea level can rise faster than would be expected from temperature trends alone. That is why long-term velocity series become crucial for understanding how Greenland behaves during a period of accelerated Arctic warming.
Jakobshavn (Sermeq Kujalleq): a speed measured in tens of meters per day
Sermeq Kujalleq, also known as Jakobshavn Glacier, has long been labeled in the scientific literature as one of the fastest outlet glaciers in the world. Sentinel-1 maps show that in some periods its speeds reached around 50 meters per day, meaning that a massive ice body moves at a pace comparable to human walking. Such episodes are not necessarily constant, but they are an important signal because changes at Jakobshavn often affect broader estimates of Greenland’s mass loss. Faster flow means a greater flux of ice into the sea, but also greater sensitivity to changes in water temperature in fjords and in ice properties. In practice, Jakobshavn is an example of how “dynamics” can accelerate ice loss even when observing only a part of the ice sheet. That is why such cases are also used as a test of model stability: if a model cannot capture such changes, it can hardly reliably project future scenarios.
NEGIS: an ice stream that begins deep in the interior
On the northeastern side of Greenland, the North-East Greenland Ice Stream (NEGIS) is also clearly visible, one of the most important ice streams that begins far inland, near the so-called ice divide. On maps, the divide appears as a belt of almost stagnant ice, while toward the coast the flow gradually accelerates and concentrates into channels. Such a view is important for models because it shows where the system is “fed” and how changes at the margin can, over years, affect deeper parts of the ice sheet. In practice, this means that changes in fjords and along the coast are not isolated, but can “spill over” to a larger area if the force balance in flows changes. A long measurement record allows such transfers of influence to be observed over time, and not only in individual episodes. This improves understanding of how large systems behave when boundary conditions change.
What the new data record enables
When the decade-long record of ice velocities is brought down to the level of practical application, it becomes a tool that serves both science and public services. In earlier periods, researchers often had to merge data from different radars, with different acquisition geometries and different noise levels, which made trend comparisons difficult. Sentinel-1, according to the study’s authors, reversed the situation by enabling regular observations in polar regions at regular intervals, so changes can be tracked with a continuity that was previously unrealistic. Beyond long-term trends, such a “dense” time series helps separate seasonal oscillations from multi-year changes and more precisely describe where the system is accelerating. Ultimately, the value of such a record is not only in a single map, but in the fact that each new year can “build on” the previous ones without fear that the change is the result of a different method.
- Baseline of ice motion: Continuous mosaics make it possible to establish a reference state of ice motion for Greenland and Antarctica under modern conditions. This is a starting point for future comparisons, especially in periods when rapid changes are expected in marginal areas.
- Early detection of acceleration: Acceleration on outlet glaciers can be the first sign of a change in ice-shelf stability, ocean temperature in fjords, or basal friction. More frequent observations reduce the likelihood that such a signal is “lost” in averages or in gaps without data.
- Monitoring events and damage: Ice velocities help interpret iceberg calving, crevasses and ice-shelf degradation, because a change in dynamics often happens before a visible surface change. In combination with other satellite measurements, it is possible to more precisely assess where the system is approaching an instability threshold.
- Better input for sea-level models: Sea-level-rise models depend on how much ice mass is transferred into the ocean, not only on surface melting. Reliable ice-velocity maps provide a more direct view of ice “drainage” and thus improve estimates of future scenarios.
Why ice velocity is the key number in the story of sea-level rise
The rise of global sea level depends not only on how much ice melts at the surface, but also on how much ice is dynamically “delivered” into the ocean through accelerated glaciers. The World Meteorological Organization (WMO) highlights in its analyses that global mean sea level depends on two major processes: the thermal expansion of the ocean as water warms and the addition of water from land ice – including the Greenland and Antarctic ice sheets and thousands of smaller mountain glaciers. In other words, even without a dramatic “collapse” of ice sheets, the combination of ocean warming and increased inflow of freshwater from land ice will push sea level upward. In that context, ice velocity is not a minor metric, but a variable that describes how quickly the system turns land ice mass into an ocean contribution. When flows accelerate, the sea gains water faster, and coastal zones become more vulnerable over shorter time horizons.
Here lies the value of satellite velocity maps: they allow estimates of ice contribution to sea level to be tied to measurable dynamics, not only to temperature trends. If a persistent acceleration appears on key outlet glaciers, it is a signal that boundary conditions are changing – for example, ocean temperature in fjords, the stability of floating ice shelves, or basal friction. Scientists therefore treat ice velocity as one of the “sensitive” variables: it can change before total mass loss becomes obvious in integrated balances. In practice, this means changes that could increase future sea-level contribution can be detected earlier. At the same time, such data help test how realistic models are, because a model that cannot reproduce observed accelerations can hardly reliably project the future. That is why climate discussions increasingly call for ice changes to be measured as systematically as temperature changes.
From scientific paper to operational maps: how the data are used
The decade-long Sentinel-1 measurement record does not remain locked in academic databases. Annual ice-velocity products for Greenland and Antarctica are available through the C3S Climate Data Store and are updated year by year, with standardized metadata and clear guidance on temporal coverage. The product description emphasizes that annual mosaics for Greenland are calculated over the glaciological year from 1 October to 30 September, and for Antarctica from 1 April to 31 March, enabling comparison with other glaciological records and seasonal analyses. Data are delivered in standard scientific formats and include uncertainty estimates, which is important for responsible use in models and analytics. In practice, this means researchers – as well as institutions working on climate assessments – gain a single “language” for comparing different regions and periods. In this way, velocity maps become a bridge between satellite observation and climate-adaptation policy.
Such operational production also changes the rhythm of research. Instead of waiting years for a new map, regular cycles make it possible to verify changes over relatively short intervals and compare them with oceanographic measurements, meteorological reanalyses or observations of iceberg calving. This also facilitates communication between science and public policy: in discussions about sea-level rise, coastal risks and infrastructure adaptation, it is increasingly important to have data that are regularly updated and can be independently verified. At the same time, such products help in education and public communication of science, because they provide visually clear depictions of dynamics in systems that are otherwise “invisible”. When a map shows how flows concentrate and accelerate, it becomes easier to understand why certain glaciers are described as key for future scenarios. Ultimately, the operational nature of such maps means ice is not observed only retrospectively, but also as a system that can be tracked in real time.
Sentinel-1 after the constellation interruption: the return of full “radar service”
Continuity of long records often depends on space logistics that are rarely visible to the public. Copernicus Sentinel-1 was originally designed as a dual-satellite constellation, but Sentinel-1B suffered a failure in 2021 in the platform subsystem that powered the radar, and its mission officially ended on 3 August 2022. Under such circumstances, the need to restore capacity is not only a technical question but also a scientific one: when the repeat rhythm is lost, it becomes harder to build comparable series and reliably distinguish short-term variability from long-term trends. In polar regions, the difference between six and 12 days is not just a number: it determines how finely rapid changes on marginal glaciers can be tracked. That is why restoring the constellation became one of the priorities of Europe’s Earth-observation system. Long records, like those shown in the study, are most valuable when maintained without interruptions.
In December 2024, Sentinel-1C was successfully launched into orbit, and on 4 November 2025 Sentinel-1D reached orbit on the European Ariane 6 launcher. ESA states that Sentinel-1C and Sentinel-1D will operate in tandem, on opposite sides of the Earth, to optimize global coverage and data delivery, and that Sentinel-1D will gradually replace Sentinel-1A, which by then had already operated for more than 11 years, significantly longer than its planned lifetime. The same release notes that the satellites carry a C-band SAR instrument, but also an AIS receiver for ship tracking, showing how the mission is designed for a broader range of public and security applications. For the cryosphere, the most important point is that this restores the possibility of more frequent and more stable acquisitions over Greenland and Antarctica, which is a prerequisite for regular production of ice-velocity maps. A more stable acquisition rhythm also means more reliable comparisons over time, and thus better estimates of changes in ice-sheet dynamics. Ultimately, satellite infrastructure becomes as important as the scientific models that rely on it.
2025 as a year of additional pressure: why denser Arctic observation is being demanded
The debate on polar changes does not take place in a vacuum. In its update on the state of the global climate, WMO highlighted that 2025 continued the streak of exceptionally warm years and, according to preliminary estimates, ranks among the warmest in the history of measurements. In the same context it notes that sea level is influenced by both ocean heat and thermal expansion, as well as land-ice loss, and that short-term oscillations in the ocean–atmosphere system can temporarily dampen or amplify trends. Such a combination of long-term warming and natural oscillations makes interpreting signals more complex, but that is precisely why high-quality, continuous data are necessary. When changes happen quickly and signals overlap, it is easy to misjudge whether it is a temporary episode or a regime shift. In polar regions, where changes are among the fastest on the planet, that question becomes particularly important.
For satellite missions this translates into a simple demand: observe more often and more reliably the areas where changes are accelerating. Ice velocity on outlet glaciers is one of the parameters that can change over months, not only over decades. If such changes are not recorded frequently enough, analysts risk lagging in interpreting causes or missing periods when the system flips from relative stability into a new state. That is why there is increasing insistence on “operational science” in the cryosphere: data must arrive regularly, in a standardized form and with uncertainty estimates. Sentinel-1 is precisely such a pillar in the European system, because it combines acquisition frequency with independence from weather and illumination. When a decade-long archive is added, a rare opportunity emerges to compare today’s changes with the relatively recent past in the same way. That level of continuity has, in practice, become indispensable for understanding polar change.
Next step: ROSE-L and the expansion of Europe’s radar capabilities
In European Earth-observation planning, eyes are already looking beyond the first generation of Sentinel-1 satellites. Among the missions being developed as part of Copernicus expansions, ROSE-L stands out, an L-band radar mission that should complement existing C-band radars and provide additional information on land, vegetation, soil and the cryosphere. In announcements, ESA emphasizes that ROSE-L is intended to deliver systematic, continuous observations and increase the resilience of Europe’s radar-monitoring system, which is important both for environmental policies and for risk management. In the context of polar regions, combining different radar wavelengths potentially increases the ability to distinguish processes at the surface, within snow and ice layers, and in interaction with the bed. Although detailed applications will depend on operational plans and data availability, the scientific logic is clear: more independent data sources reduce the risk of observation interruptions. And when observing a system that is changing rapidly, interruptions are often the most costly.
For scientists working on ice, the combination of different radar wavelengths and longer time series means greater resilience of the observing system. If one mission encounters technical difficulties, another can bridge the gap, and differences in radar sensitivity can help better distinguish surface processes from those linked to the bed or the ocean. Ultimately, the idea is simple but far-reaching: the more precisely we measure how ice moves today, the better we will understand how quickly coastal zones may change tomorrow – and how much that shift will spill over into global sea level. The study on a decade of Sentinel-1 ice velocities shows that this approach is already practically possible at continental scale, and that long-term satellite observations are no longer a scientific “luxury” but a necessary tool for understanding climate risks. In years when global temperature and ocean anomalies accumulate, the value of such series grows because they allow changes in polar regions to be measured rather than guessed. And for sea level, measurement is the first step toward more realistic adaptation planning.
Sources:- Remote Sensing of Environment – scientific article on ten years of mapping polar ice velocities with Sentinel-1 data (link)
- Copernicus Climate Change Service (C3S) / Climate Data Store – description of the operational dataset “Ice sheet velocity for Antarctica and Greenland” (link)
- ESA – press release on the launch and orbit insertion of Copernicus Sentinel-1D (4 November 2025) (link)
- Copernicus – news on the successful launch of Copernicus Sentinel-1C (December 2024) (link)
- Copernicus Sentinels – notice on the end of the Sentinel-1B mission after failure and recovery attempts (link)
- WMO – article on the causes and uncertainties of future sea-level rise (link)
- WMO – update: 2025 among the warmest years and the context of ocean heat, ice and sea level (link)
- Remote Sensing of Environment – list of collections and special issues (including the collection dedicated to a decade of Sentinel-1) (link)
- ESA – overview of Sentinel-1 applications and the role of radar in observing ice and crisis situations (link)
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