In the cover article of the latest issue of the Journal of Glaciology, engineers at the University of Kansas detail a special radar array they developed that is capable of depicting a 3D view of bedrock hidden beneath ice sheets 3 kilometers thick.
Working at the National Science Foundation Center for Remote Sensing of Ice Sheets at KU, the researchers, led by then doctoral student John Paden, designed a Synthetic Aperture Radar system that provides a fine-resolution image of the bed over a wide geographic region, as well as the thickness of the ice. Topographic characteristics of earth below the glaciers and ice sheets have long been sought after. It is considered essential information to develop computer models that can better predict the role of ice sheets in global climate change and sea level rise.
The radar system is a game-changing development for researchers in global climate change. Previously, glaciologists could only know the thickness of the ice and bed conditions along a single line from a sole pass of a radar or at a single point where ice core samples had been drilled.
To get these innovative 3D landscapes, KU engineers constructed a special sled with several radar transmitters and receivers. The sled was then hauled over Summit Camp in Greenland, following a precise grid of parallel lines 500 meters apart connected by perpendicular lines. The radar used both left-looking and right-looking beams in the frequency needed to broadcast television signals. Researchers used advanced signal processing techniques that determined the directions of the echoing wavelengths. The team of researchers was able to collect data that essentially peer through ice as much as three kilometers thick and reveal the ground from multiple points.
Since the same spot on the ice bed is imaged by radars from several tracks, the elevation is independently measured multiple times, Paden wrote in his paper. Paden received his doctorate in electrical engineering from KU in 2007. He’s now employed as a software development engineer with Microsoft’s Vexcel Corporation.
“While the 2D representations provide a consistent medium for comparison of point differences, a 3D representation provides better visualization and interpretation of surface features,” Paden wrote. To confirm accuracy, researchers compared their result with the length of the 3,027 meter long GRIP ice borehole, and found their data to be within 10 meters at that site. The radar system is considered very accurate with an error of 0.3 percent in the index of refraction, well within acceptable limits for ice-penetrating radars.
The Intergovernmental Panel on Climate Change estimated that sea level would increase from 18 to 59 centimeters over the next century. The success of this radar system will help researchers obtain needed data in the effort to create more accurate ice-sheet models that predict sea level rise, Paden wrote. The new radar system can be carried by airborne vehicles and also will help glaciologist identify locations ideal for future ice core sampling.
Paden worked with KU engineering professors Chris Allen and Prasad Gogineni, director of CReSIS; CReSIS engineer Torry Akins; and then graduate student David Dunson. All are KU engineering alumni.