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Scientists commonly use radar technology to analyze glaciers and ice sheets where direct observations are difficult to obtain. A new article in Reviews of Geophysics focuses on one specific radar application called “radar polarimetry,” which is primarily used to measure the orientation of ice crystals. Here, we asked the authors to give an overview of radar polarimetry, the benefits of using it, and future directions for use.
In simple terms, what is radar polarimetry?
Radar sounding is a geophysical method used to explore the structure and composition of the subsurface and a crucial tool in glaciology. It works by transmitting radio waves and measuring the signal that bounces back from within and underneath ice. Those radio waves oscillate in a particular direction — their “polarization.”
Radar polarimetry is the practice of transmitting and receiving waves with different polarizations.
Radar polarimetry is the practice of transmitting and receiving waves with different polarizations to learn more about either the material the waves traveled through or about the surface from where they were reflected. Think of polarized sunglasses: they only let through light oscillating in one direction, which is why they reduce the glare off water. Similarly, when polarized radar waves pass through glacier ice, the ice can rotate or reshape the wave’s polarization depending on its internal structure. By carefully measuring those changes, scientists can reconstruct properties of the ice that would be invisible or considered noise to a conventional radar.
When was radar polarimetry first developed? When did glaciologists start using it?
Radar polarimetry has roots in remote sensing, dating from the 1970s and earlier. Glaciologists recognized early on that ice could alter radar wave polarization, with the first field confirmation in 1977 when Hargreaves measured polarization-dependent radar signals in Greenland’s ice sheet. Throughout the 1980s and 1990s, several groups in Antarctica and Greenland observed similar effects, but lacked the tools to interpret them quantitatively. The turning point came in 2006, when Fujita et al. published a mathematical framework connecting polarimetric radar measurements directly to the alignment of ice crystals deep within glaciers. That framework became the foundation for modern analyses and opened the door to using radar as a tool for mapping ice crystal structure remotely. In the two decades since, the method has grown from a niche technique into a widely adopted tool, with new instruments and analyses enabling routine measurements across both ice sheets.
What innovations on instrument hardware or data analysis breakthroughs have led to increased adoption of radar polarimetry as a glaciological tool in recent years?
The most important hardware development has been the widespread adoption of phase-coherent radar systems, which measure not just the strength of returned signals but also their precise timing (i.e., the phase of the wave). This precision allows scientists to detect the subtle polarization changes caused by ice crystal alignment. One such instrument — the Autonomous phase-sensitive Radio Echo Sounder, or ApRES, has become particularly popular because it is portable, affordable, and widely accessible.
Building on this, several groups have developed multi-antenna systems that capture the full set of polarization measurements simultaneously, without manually rotating antennas. These multi-antenna designs are also being adapted for airborne platforms, enabling polarimetric profiling over hundreds of kilometers in a single flight. Additionally, new analysis methods allow for radar polarimetric interpretations from conventional single-polarization surveys, particularly when transect lines cross each other, meaning decades of existing data can be reanalyzed to extract novel glaciological insight.
What information can radar polarimetry tell us about glaciers and ice sheets?
Radar polarimetry reveals how the many tiny ice crystals inside a glacier are collectively aligned.
Radar polarimetry reveals how the many tiny ice crystals inside a glacier are collectively aligned, what glaciologists call “crystal orientation fabric.” This fabric develops over thousands of years as ice deforms under its own weight, and it controls how easily ice flows in different directions. Understanding the fabric is therefore essential for both reconstructing past ice flow and anticipating how ice sheets will respond to continued warming, ultimately improving predictions of future sea-level rise.
What are the major advances in glaciology that have been made as a result?
Major advances include mapping crystal fabric across wide regions for the first time, rather than relying on a handful of expensive ice cores. At the Northeast Greenland Ice Stream, which drains approximately 12% of the Greenland Ice Sheet, researchers combined multiple polarimetric methods with ice-core measurements to show how crystal fabric varies spatially and affects large-scale ice flow. In Antarctica, similar techniques have identified changes in ice-flow regimes in fast-flowing regions critical for sea-level projections.
What are the benefits of using radar polarimetry to study glaciers over other methods?
The most direct way to measure ice-crystal alignment is by drilling an ice core and examining thin slices under a microscope. However, ice cores are expensive, logistically demanding, and each one samples only a single point. Moreover, ice cores are generally drilled in slow-flowing regions to capture long climate records, leaving a dearth of fabric measurements in dynamic, fast-flowing areas. Seismic methods can also detect crystal alignment but require heavy equipment, a seismic source like explosives, and dense sensor networks.
The instruments are lightweight, inexpensive, and easy to deploy in remote polar environments.
Radar polarimetry fills this gap: the instruments are lightweight, inexpensive, and easy to deploy in remote polar environments. A single ground-based radar can be carried by a small team on a snowmobile, whereas airborne radar can survey hundreds of kilometers in a single flight. Beyond crystal orientation, polarimetric radar can also map directional properties of the ice-bed interface that are crucial constraints on ice-flow dynamics.
What are the future directions for radar polarimetry?
The most immediate frontier is scaling up. As multi-polarization radar systems are mounted on aircraft and ground-based traverses cover longer distances, comprehensive mapping of ice-crystal orientation fabric and directional roughness of the ice-bed interface at regional and even continental scales is becoming feasible for the first time. This spatial coverage will be transformative for ice-sheet models, which currently rely on sparse or assumed fabric distributions. A second frontier is wide-angle surveys, where the antennas are separated by large distances, which should allow scientists to resolve the full three-dimensional fabric rather than just the horizontal component that current methods capture. Beyond Earth, upcoming missions to Jupiter’s moons — the JUICE and Europa Clipper spacecrafts, arriving around 2030, will carry radar instruments to sound through thick ice shells where polarimetric techniques could reveal internal dynamics and ice-flow history.
—Benjamin H. Hills (benjaminhhills@gmail.com, 
0000-0003-4490-7416), Colorado School of Mines, United States; T. J. Young (0000-0001-5865-3459), University of St Andrews, United Kingdom; David A. Lilien (0000-0001-8667-8020), Indiana University, United States; Tamara A. Gerber (0000-0002-0368-7229), Université de Lausanne, Switzerland; and Matthew R. Siegfried (0000-0002-0868-4633), Colorado School of Mines, United States
Editor’s Note: It is the policy of AGU Publications to invite the authors of articles published in Reviews of Geophysics to write a summary for Eos Editors’ Vox.
Citation: Hills, B. H., T. J. Young, D. A. Lilien, T. A. Gerber, and M. R. Siegfried (2026), How radar reveals the hidden fabric of ice sheets, Eos, 107, https://doi.org/10.1029/2026EO265007. Published on 9 March 2026.
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Text © 2026. The authors. CC BY-NC-ND 3.0
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