Radar sounding and imaging of fast-flowing glaciers in Greenland

Radar sounding of fast-flowing glaciers is a major challenge. The surfaces of these glaciers are extremely rough, and they contain lossy ice. The off-vertical surface-clutter returns that arrive at the same time as ice-bed echoes often masks weak bed echoes. Synthetic Aperture Radar (SAR) processing techniques can be used to reduce along-track clutter; however, this is ineffective in reducing cross-track clutter. For this reason, we developed a multi-channel radar depth sounder/imager that can be operated with a cross-track array of 6–15 antennas. We have been operating this system on a Twin Otter aircraft with 12 antennas mounted under both wings of the aircraft. We used 6 of 12 elements for transmission and reception and 6 elements only for reception. We are also operating the radar with 15 antennas on the NASA P-3 aircraft as a part of NASA´s Operation IceBridge (OIB). We applied advanced array processing techniques to reduce cross-track clutter and successfully sounded key glaciers in Greenland. We have also used data collected with the cross-track array to generate fine-resolution 3-D topography. In this paper, we will provide an overview of the design and development of radars, antenna arrays and their performance, and discuss signal processing algorithms and results over key areas of the Greenland ice sheet.