The Center has developed radars that operate over the frequency range from 140 to 230 MHz with multiple receivers developed for airborne sounding and imaging of ice sheets. The radar bandwidth is adjustable from 20 MHz to 60 MHz. Multiple receivers permit digital beamsteering for suppressing cross-track surface clutter that can mask weak ice-bed echoes and strip-map synthetic aperture radar (SAR) images of the ice-bed interface. With 200 W of peak transmit power, a loop sensitivity > 190 dB is achieved. These radars are flown on twin engine and long-range aircraft including NASA P-3 and DC-8.
The Center has also developed an eight-channel wideband radar for surface-based sounding and imaging of the ice-bed interface. It operates over the frequency range from 120 to 230 MHz to provide 1-m depth resolution in ice. Digital beamsteering with the eight-element receive array permits imaging 1-km swaths centered 1 km from the nadir track as the radar moves along the ice surface 3 km above the bed. Data collected with this radar can be processed with interferometric and tomography techniques [Paden et al., 2010], to generate detailed digital elevation maps of the bed.
Fine depth resolution profiling of the top 100 m of the ice column is achieved with this radar designed to map variations in the snow accumulation rate. When operated from aircraft, it operates from 600 to 900 MHz providing 28-cm depth resolution in ice and when operated on the ground (500 MHz to 2 GHz) a 5.6-cm depth resolution in ice is achieved. This fine depth resolution enables area extensive spatial mapping of the annual accumulation layers.
The Center has developed an ultra-wideband radar that operates over the frequency from 2 to 8 GHz to map near-surface internal layers in polar firn with fine vertical resolution. The radar has also been used to measure thickness of snow over sea ice. Information about snow thickness is essential to estimate sea ice thickness from ice freeboard measurements performed with satellite radar and laser altimeters.This radar has been successfully flown on NASA P-3 and DC-8 aircraft.
Ku-band Radar Altimeter
The Center has been developing a wideband radar altimeter that operates over the frequency range from 13 to 17 GHz. The primary purpose of this radar is high precision surface elevation measurements over polar ice sheets. The data collected with this radar can be analyzed in conjunction with laser-altimeter data to determine thickness of snow over sea ice. The radar has been flown on a NASA DC-8 aircraft, and the NSF provided a Twin Otter aircraft.
An eight-channel, 195-MHz center frequency, 30-MHz bandwidth radar is being developed specifically for operation aboard the Meridian UAS. This radar, which uses an array of 4 broadband Vivaldi antennas under each wing, will provide depth sounding data (1.9-m depth resolution in ice) and SAR imaging of the ice-bed boundary from a 500-m altitude. Digital beamsteering on transmit will enable illumination of swaths at nadir, and to the left and right of nadir on alternating pulses.
3-D Imaging Radars
Since the summer of 2005, the CReSIS radar depth sounder/imagers have used cross-track antenna arrays to capture multi-phase center SAR data for use in 3-D tomographic processing (Paden 2006, Paden 2010, Blake 2010). The cross-track arrays have varied between five and 16 phase centers, depending on the platform. By applying adaptive array processing techniques to these data, we have produced fine-resolution digital elevation models of the ice bottom and performed englacial imaging. We have recently completed an algorithm for routine 3-D ice bottom image and surface extraction for airborne mapping. Examples from the 2009 Antarctica Twin Otter and the 2010 Greenland P-3 missions are shown here.
This material is based upon work supported by the National Science Foundation under Grant No. ANT-0424589. Any opinions, findings, and conclusions or recommendations
expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.