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Radio waves

Using radio waves to peer through thick layers of ice
1 Antarctica may seem like nothing but ice, but those glaciers cover mountains as tall as the Rockies and a lake almost as big as the state of Connecticut. And the ice sheet itself holds enough water to raise sea level by an estimated 190 feet (58 m) around the world. Radio glaciologists, like Dustin Schroeder of Stanford University, use radar to study the ice and get a glimpse of the hidden landscape below. But they don’t do it by digging down through the ice. They do it by flying high above.
2 Getting a glimpse beneath the icy surface is about far more than exploration. What glacial ice is made of, how cold or warm it is, and whether it is sitting on top of water or bedrock can all dramatically affect how the ice will behave. And how ice behaves can be the difference between some minor melting and a catastrophic collapse.
3 It may be hard to picture, but Antarctica’s massive ice sheets flow over Earth’s surface. Some glaciers move easily over fine sediment and liquid water. Other glaciers move slowly over surfaces such as hard bedrock or steep cliffs. Ice sheets with thick edges flow more quickly than thinner ones. Even the structure of the ice crystals at the tiniest scales can change how massive bodies of ice will flow. So getting measurements of how thick an ice sheet is and the kind of material it’s sitting on is important for figuring out how quickly it might move or change.
4 Just as important as how a particular ice sheet moves is how it melts. Every year, growth and melting occur with the seasons. When climate change causes additional melting, it can be too extreme to gain back. Ice shelves, with warm ocean water touching their bases, can melt particularly quickly. And not all melting happens at the surface or the base. Some water ends up stored in pores within the layers of ice itself. Getting an idea of when and how an ice sheet might melt means getting a look inside.
5 Many of the traditional tools we use for mapping are designed for studying features at the surface—like a detailed picture of the frosting decorations on a cake. But how do you get a look inside? Scientists can’t just take a mile-thick slice of a glacier, so they depend on tools like radar. Radar technology measures the time it takes for a signal to reach a surface and bounce back to the sensor. It’s similar to timing an echo. Scientists use this timing to calculate distance.
6 Radio glaciologists send bursts of radio waves that travel at the speed of light. The waves can pass through solid objects like rock and ice before they bounce back. The process is so fast that the device sending the signal and the antenna receiving it can be part of the same instrument. The whole system can even take measurements from a plane flying over the landscape. The result—a radargram—provides a view beneath the surface in the path of the plane. According to Schroeder, the radar reflections pick up tiny changes in density or materials in the layers of ice and provide a profile of the continental bedrock below. The radar can’t look through water because the reflection of the signal is too strong. But it is a valuable tool for seeing if liquid water is present, even in tiny amounts.
7 Schroeder gets excited about using radar to study ice not just because of what he gets to study, but also because he gets to be a part of developing the tools to study it. Whereas many other areas of science have been around for centuries, radio glaciology feels young by comparison. Researchers are still figuring out exactly which questions to ask, so the people designing instruments and the people posing the questions have to work together very closely. Sometimes, they are even the same people. Because of his passion for scientific instruments, Schroeder thinks this crossover between science and engineering is an exciting place to be.