Between 1979 and 2023, the Antarctic Ice Sheet lost on average 107 Gt of ice per year, contributing a total of 13.4 mm to sea level rise. As global temperatures continue to rise, accelerated melting is expected as well as increased contributions to global sea levels.

Tracking that loss accurately depends on satellites measuring ice sheet height from space and on understanding exactly how robust those measurements are over complex terrains in the cryosphere.

New research from CPOM, published last week in The Cryosphere led by Joe Phillips and Mal McMillan at Lancaster University used REMA, the Reference Elevation Model of Antarctica, a highly detailed map, to assess of the Sentinel-3 radar altimeter’s performance across the Antarctic Ice Sheet.

About Sentinel 3

Sentinel-3 has provided operational SAR altimetry coverage of Antarctica since 2016. Although primarily designed for ocean and land monitoring, it includes a high-resolution radar altimeter capable of measuring ice sheet elevation and sea ice thickness change. Thus, it a valuable operational complement to ESA’s CryoSat-2 Earth Explorer mission, the first such radar altimeter satellite primarily dedicated to studying the Earth’s ice.

Radar altimeters, like Sentinel-3’s however face a challenge in that measurement quality tends to degrade where terrain gets steep and rough, such as at the margins of ice sheets.

The study

The research used REMA to assess how accurately Sentinel-3 captures measurements over the Antarctic Ice Sheet’s complex terrain. Recent advances in data processing have allowed more data to be retrieved with over 94% of acquisitions successfully capturing the point of closest on the ice surface. A key requirement for reliable data is that the instrument records the point of closest approach on the ice surface, something made harder by Sentinel-3’s relatively narrow 60 m measurement window.

In this regard, the study showed how increasing the window size made a substantial difference. For example, with a 240 m window, like that operated by CryoSat-2, there was near-complete (99%) surface capture across the entire ice sheet, including the most complex margins (compared to a mean capture of 90.6% at 60 m). This is an important consideration for future missions, such as the Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL).

About Radar Altimetry

Radar altimetry works by firing pulses of microwave energy at Earth’s surface, timing how long it takes for the echo to return, giving a precise measurement of surface elevation. The echoes are recorded as a power waveform, (the echo returning through time), and the elevation measurement is taken from the first steep rise of the waveform with the assumption being that this peak relates to the Point of Closest Approach (POCA) giving a single elevation measurement per echo. Satellites return an echo of a limited recording window of time (range window), but if this is misplaced, the echo from the surface can be missed. Although previous assessments of Sentinel-3’s radar have focused on validations of the final elevation products, more detailed assessments of the instrument and processor performance are less common.

About the study

The team investigated how much of the ice sheet surface Sentinel-3 captures within its range window, whether the leading edge of the waveform can be attributed to the closest point on the surface, how consistently radar echoes look from one measurement to the next; and the role that key surface topography characteristics such as slope and roughness play on all of these effects.

They analysed over 8 million radar echoes from Sentinel-3A and 3B, comparing the latest processing version (BC-005) against its predecessor (BC-004) and produced accurate, continent-wide maps of ice surface slope and roughness from the Reference Elevation Model of Antarctica (REMA), a 100 m resolution mosaic built from satellite stereo imagery.

The results of the study found that for 57.4% of acquisitions, capturing 100% of the illuminated surface is impossible with the current 60 m window. It also found that, on average, Sentinel-3’s placement of the range window captured 89.2% of the maximum topographic signal that could be recorded within its range window.

By exploring the hypothetical impact of increasing the window size, the study found that this made a substantial difference. For example, implementing a 240 m window, like with CryoSat-2, there was near-complete surface capture across the entire ice sheet, including the most complex margins (compared to a mean capture of 90.6% at 60 m).

The study also produced the first slope-independent roughness map of the entire Antarctic continent (to their knowledge). The code for this can be found at https://github.com/Joe-Phillips/SAR-Altimetry-Flyover-Visualiser and a clip of the animation can be seen at the top of this article.

The future of radar altimetry for monitoring Antarctica

This bodes well for future retrievals from the CRISTAL mission, with its 256 m window. CRISTAL is ESA’s next-generation polar ice altimeter, planned for launch in 2027, and the successor of the CryoSat-2 mission.

By identifying and quantifying one of the main challenges of previous generations of altimetry – performance over complex Antarctic terrain – this study provides a strong evidence base for the next generation of instruments.

It’s vital we have the most accurate understanding of current and future ice loss, so we can plan for future changes in global sea levels.

The only way this is possible is by assessing, calibrating and improving the data we retrieve from satellite missions like Sentinel-3 and CryoSat-2 and informing future satellite missions like CRISTAL.

All image credits: Phillips, J. and McMillan, M.: Assessment of Sentinel-3 altimeter performance over Antarctica using high resolution digital elevation models, The Cryosphere, 2026.

A study published in Geophysical Research Letters on 09 March 2026 projects that by 2067, ice loss from Thwaites Glacier in West Antarctica could be 180-200 billion tons of ice per year, almost the current annual losses from the entire Antarctic ice sheet.

The study, led by Dr Dan Goldberg (University of Edinburgh) with co-authors Professor Noel Gourmelen (University of Edinburgh) and Professor Mathieu Morlighem (Dartmouth), tested two independent ice sheet models (STREAMICE and ISSM), training them using two types of satellite observation: velocity change from interferometry, and surface elevation data from altimetry missions.

The research found that calibrating models solely using surface elevation change data produced volume change predictions which were ten times more accurate than those using ice speed data. This shows the choice of calibration method has a significant effect on long-term projections.

This research is funded in the context of ESA’s 5D Antarctica project within the Polar Science Cluster.

Read more about this research on the ESA EO Science For Society website.

More information on the research

Goldberg, D. N., Morlighem, M., & Gourmelen, N. (2026). Recent observations of Thwaites Glacier, West Antarctica are consistent with high rates of loss in next 50 years. Geophysical Research Letters, 53, e2025GL118823. https://doi.org/10.1029/2025GL118823

News feature image credit: Professor Andrew Shepherd

Research from education charity Teach First in 2024 found that more than half of girls (54%) lack confidence studying maths compared to 41% of boys, with the gap even wider for science where 43% of girls say they lack confidence compared to only 26% of boys despite the fact that girls often outperform boys in these subjects. The consequences reach beyond the classroom: women only make up 26% of the UK’s Core-STEM workforce.

This International Women’s Day, we want to highlight how important it is to support girls to study STEM at school. This blog by CPOM PhD Researcher Alicia Fallows (UCL), explains how her teachers and family encouraged her journey into polar science, which has already taken her to the Arctic Circle.

Blog by Alicia Fallows

How a love of Physics at school led Alicia to the Arctic Circle

I’ve always adored the natural world and based upon my favourite subject at A-Level decided to pursue my undergraduate degree in Physics as a way to delve into this planet and its components.

Along the way I became very interested in quantum physics, something I still find fascinating, and followed a Master’s in a similar field. Towards the end of my Master’s I realised I wanted to apply my skills to something more tangible and come back to my love for the natural wonders of this planet, encouraged even more so in the context of climate change.

After working for a few years, I found the London NERC DTP as a perfect way to come back to research with a brilliant network of academics offering exciting PhD projects. By this time, I knew I wanted to focus on snow and ice, in part due to a love of glaciers formed visiting Mont Blanc when I was 17, as well as from watching David Attenborough’s Frozen Planet! I also felt the cryosphere was being heavily impacted by our changing climate.

I didn’t set out for a project specifically dedicated to the polar regions, as I didn’t even know it would be something within my reach. After meeting with my (now) supervisor Rosie (Dr Rosemary Willatt, UCL and CPOM), I realised how I could transfer my skills to sea ice and snow physics, with a focus on some of the most remote and important parts of our planet!

I feel lucky to have a family that have always supported me to pursue anything I wanted and additionally encouraged me to cherish our planet by getting outdoors a lot from a young age (not being afraid to get mucky). Time spent outside hiking, often with our beloved dog, and witnessing my families interests in botany, geology and adventure, only made me more interested in the sights I saw and the science behind them.

I was fortunate enough to have a few brilliant science teachers in both school and sixth form college who believed in me and supported my ambitions to study further, as well as showed their passion for physics and chemistry. And some brilliant drama/dance teachers who helped me to build confidence!

My parents were instrumental in my choice to apply to university, and my friends and partner have supported me throughout the years. At university my undergraduate dissertation supervisor was incredibly encouraging and made me believe I was capable to stay within science in the future. Nevertheless, turning up to a physics degree as one of a handful of women, with only a handful of women lecturers, was daunting. I hope we can turn this around further to encourage more girls and women to not only come into science, but to stay in it. Last year I was lucky enough to be part of an all-women field team – so hopefully we are on a good trajectory!

It never occurred to me the range of interdisciplinary subjects that can be studied at university, and being a scientist was never presented to me as a choice at careers meetings. I am grateful to have studied physics and the flexibility this has given me, but I’d like girls to know that there are so many options out there and the path doesn’t always have to be straightforward!

Stories like Alicia’s show why it’s so important to encourage all children and young people to engage with science. That’s we’ve created resources to help parents and teachers introduce children and young people to polar science.