Single airborne radar profiles of Ferrar Glacier and the upper reaches of Taylor Glacier were obtained by the cooperative National Science Foundation / Scott Polar Research Institute (NSF/SPRI) program of the late 1960’s (Calkin, 1974). One of the earliest airborne radar sounding programs in Antarctica, it utilized a 35 MHz pulse-modulated transmitter with incoherently detected returns that were optically recorded with an emphasis on measuring ice thickness and subglacial morphology. Beyond providing context, these data are of little value for establishing terrestrial analogs for Mars. This early work was complemented by a more systematic NSF/SPRI survey in the mid 1970’s of the upper reaches of Taylor Glacier including Taylor Dome which is a local center of ice flow. The dual frequency data (60 and 300 MHz) show much more englacial detail but are also optically recorded. In addition, there is no published coverage of the “ice-free” portion of either Taylor or Beacon Valley so they are of limited value for Mars analog radar studies.

There has also been a more recent ground-based radar study in lower Taylor Valley (Arcone et al., 2000). This study utilized a modern digital radar system and while limited in scope, it serves as useful ground truth for airborne radar studies.

The University of Texas Institute for Geophysics (UTIG) has been collecting airborne geophysical data in Antarctica since the early 1990's (e.g. Blankenship et al., 1993; 2001) using a modified deHavilland Twin Otter. Instrumentation has consisted of an ice-penetrating radar, laser altimeter, a gravimeter, and a magnetometer. A complete suite of secondary instruments characterize the airplane's position and attitude during flight. The most critical of these are the inertial navigation system (INS) and differential kinematic carrier-phase GPS receivers which are operated in tandem with receivers at a base station. Post-processing of GPS data yields positioning to ~0.10 m accuracy at 0.5 sec intervals.

The ice-penetrating radar used by UTIG for much of its aerogeophysical research has been a 60-MHz pulsed continuous-wave radar with peak transmit power of 8 kW with an incoherent logarithmic detector. This radar was originally designed by the Technical University of Denmark (TUD) for use on a LC-130 Hercules platform by the NSF/SPRI program in the 1970’s (see Drewry et al., 1983). In the early 1990’s it was modified for use in a Twin Otter by UTIG. In the mid 1990’s it was integrated with a new digital acquisition system with a 16 ns digitizer capable of integrating 2048 transmissions every 10 m along track. The Twin Otter installation utilizes two of the original four dipole antennas of the system as implemented on the LC-130. UTIG has used this basic system to collect over 300,000 line-km of aerogeophysical data in Antarctica.

Coherent radars are essential to fully characterize subsurface interfaces (Gogineni et al., 1998; Peters et al., in review). In the late 1990’s UTIG entered into a collaboration with the Jet Propulsion Laboratory (JPL) to test a prototype coherent radar sounder in Antarctica. This was to be a variable frequency radar transmitter with controllable chirp and pulse length coupled to a receiver with two coherently detected channels and 12-bit digitizers (Moussessian et al., 2000). JPL designed and built the radar signal source and receiver, purchased an off-the-shelf transmitter (500W), and contracted the University of Kansas (KU) to design and build the data acquisition system. During initial field tests in January, 2000, UTIG and JPL engineers replaced the original transmitter with a UTIG-modified TUD transmitter stage (750 W peak output power) due to excessive noise in the commercial transmitter. Data were collected in the Dry Valleys region (Taylor Valley, Taylor Glacier, Taylor Dome, and Ferrar Glacier) using both the UTIG/TUD radar and the JPL/KU/TUD radar. Following these field tests, the JPL/KU radar system was subsequently transferred to UTIG for future use in research.

In 2001, UTIG returned to Antarctica with a fully integrated coherent radar system and the objective of developing new radar sounding techniques for a variety of over-ice targets in East and West Antarctica. The goal was to develop system configurations for maximizing penetration in warm ice and heavily crevassed regions, resolution of internal ice layers, and subglacial interface characterization. The Dry Valleys region was used for system tests while the airborne platform was being configured and tested at McMurdo Station. The radar system was comprised of the JPL signal source, the high-power 8 kW TUD transmitter, and three separate receiver systems. The radar was operated at a center frequency of 60 MHz with a 15-MHz-bandwidth chirped pulse (centered at 60 MHz), typically of 1 µsec duration. Pulse repetition frequency was 6.4 kHz. The receivers used in this system were:KU coherent acquisition system. Samples downconverted signal (2.5 – 17.5 MHz) at 20 ns. 16 radar sweeps were stacked.

UTIG-designed coherent system: Samples 52.5 – 67.5 MHz signal at 4 ns, stacks of 256 and 1024 sweeps.
UTIG/TUD incoherent system with log-detection: Samples 52.5 – 67.5 MHz signal at 16 ns, 2048 stacked sweeps.

A laser altimeter (fixed relative to the aircraft frame) was also used during both seasons. Post-processing of the positioning data yields accuracies of ~ 0.10 m for samples at ~ 15 m intervals.