Frozen secrets: Geophysicist explores glaciers with radar
“In some ways, we know more about the surface of Mars than we do about what’s beneath the Antarctic Ice Sheet,” according to Dustin Schroeder, a radio glaciologist at the School of Earth, Energy & Environmental Sciences (Stanford Earth).
Schroeder shared his research on ice-penetrating radar during a May 17 talk titled Radar Glaciology: A Window into Ice. Community members, students, and Stanford faculty attended the event, which was part of the Earth Matters lecture series co-sponsored by Stanford Continuing Studies and Stanford Earth.
Schroeder’s research is important for understanding climate change, since ice sheets and glaciers – slowly moving masses of ice – regulate conditions for the whole planet. Located in the Antarctic and Greenland, their stability greatly impacts how quickly oceans will rise, by how much, and how that will affect the rest of the climate system.
But making predictions about glaciers and ice sheets requires researchers to observe and understand changing conditions beneath kilometers of ice.
“We can predict weather reasonably well,” said Schroeder, who is also an affiliate at the Stanford Woods Institute for the Environment. “But when you’re talking about the collapse of an ice sheet, it’s less like predicting weather and more like earthquake prediction.”
Schroeder’s research focuses mainly on the Pine Island and Thwaites Glaciers, which comprise two of the five largest ice streams in Antarctica. While these glaciers are just one component (along with Greenland and mountain glaciers) to current rate of sea level rise, their possibility of collapse could dramatically increase that rate. Like most glaciers in West Antarctica, they sit below sea level, and their exposure to ocean water creates potential instability.
“If a retreat starts there, it could spread to the rest of the ice sheet,” Schroeder said. “From my perspective, heat from the ocean is driving change, but it’s what’s happening underneath that determines how the ice sheet responds.”
Vestiges of war
Much of the data Schroeder uses to analyze ice sheets is collected by air-borne radar technology developed by different nations during WWII. Displaying a photo of a WWII-era DC-3, a fixed-wing propeller-driven airplane, he explained how antennas beneath the wings transmit radar downward. The information reveals the activity beneath and within the ice sheet. While ground-penetrating radar can only measure a few meters through land, ice-penetrating radar can reach three kilometers below the surface.
“Ice is very cooperative as a medium,” Schroeder said. “It’s a lot more like air than it is like the Earth in terms of measuring it.”
With information collected from these surveys, the researchers analyze radargrams, or visualizations of the data that show a vertical profile through the ice sheet – like a slice of layer cake. Similar to tree rings, the layers reveal information about the history of the ice sheets.
“One of the challenges our team works on addressing is how to interpret data from different radar systems, flown on different aircraft, at different speeds, and with different processing,” Schroeder said. “The hope is that as we start to develop cross-system processing approaches for this data, we can piece together a holistic picture of what’s happening beneath the ice sheet.”
I deeply believe that groups of hyper-talented, passionate young people can solve most of the pressing problems facing our world.
An interdisciplinary approach
Ice-penetrating radar is the best tool for understanding ice sheets, but researchers need to use innovative methods in data processing, analysis, and modeling to create a complete picture of the glacial system. Some techniques offer broad, three-dimensional coverage, but cannot reveal patterns over long periods of time. The reverse is also true – technologies that show changes over time can only do so in a small area.
“I spend a lot of time existing between engineering and science,” said Schroeder, who worked as a radar systems engineer with the Jet Propulsion Laboratory at the California Institute of Technology before joining Stanford as an assistant professor of geophysics in 2016. “I was always trying to come up with this one processing approach that could answer everything – but that limits the kinds of solutions you can pursue. The problems we’re working are challenging enough that you need to develop custom approaches for each one.
Collaborating with faculty members in geophysics, engineering, and Earth systems to understand ice, Schroeder constantly challenges traditional methods for collecting data. His Radio Glaciology research group aims to develop solutions for revealing large areas of ice sheets over long periods of time – and their models need to include all of the physics, processes, and conditions that regulate glacial behavior.
“By training engineering students that can think like Earth scientists and Earth science students that can think like engineers, our group is creating an environment where instruments can be built for exactly the specific scientific problem at hand,” Schroeder said.
The final frontier
Because they share similar physics and processes as glaciers, icy moons can also be explored using ice-penetrating radar. By participating in NASA’s Europa Clipper Mission to study Europa, one of Jupiter’s moons, Schroeder helps scientists better understand if the icy moon could support life.
He discussed how radio emissions on Jupiter could provide a signal for passive radar sounding – a technique he hopes his team can develop on Earth.
“The biggest cost is power used to transmit the radar, so it would be great to use radio signals that are in the environment,” Schroeder said.
Schroeder works with undergraduate students to develop methods for harnessing the Sun’s radio frequencies to look through ice sheets and glaciers. He displayed a photograph of a prototype radar in Big Sur developed by Stanford electrical engineering undergraduates and described their fast-paced innovation in today’s maker movement as “one of the coolest, best parts of the job.”
“I deeply believe that groups of hyper-talented, passionate young people can solve most of the pressing problems facing our world,” he said.
Schroeder is a science team member on NASA’s Europa Clipper mission and served as lead radar engineer and operator during three Antarctic field seasons with the ICECAP project. His latest research, published May 24 in The Cryosphere, describes how to improve estimates of the roughness and thermal state of the bed of the Greenland Ice Sheet using radar-sounding data.