High resolution of glacial ice stratigraphy: A ground‐penetrating radar study of Pegasus Runway, McMurdo Station, Antarctica

Abstract

Ground-penetrating radar (GPR) has been used to detect areas of present or potential structural weakness beneath a 3.2-km snow-covered ice runway on the Ross Ice Shelf, Antarctica. The bandwidths of the transmitted wavelets were centered near 500 MHz. The data show many horizons up to tens of meters long and occurring to about a 9-m depth, below which a brine intrusion limits penetration. The horizons are interpreted as discrete scatterers because of their diffraction nature and loss of higher frequencies with depth. The presence of porous ice or dispersed water is interpreted from wavelet phase. The water may be associated with apparent deepening and fading of the brine horizon. If the above interpretation is correct, water occurs at depths to 3.5 m and extends as much as 40 m horizontally, which is greater and deeper than known previously. At 3.5 m depth, the water may be adsorbed on mineral particles rather than remain free. Migration of the diffractions with a singlelayer migration scheme shows all horizons above the brine layer to be small dielectric perturbations within the ice. Stacking and Hilbert transformation of the data reveal slight folding along the length of the runway. Loss of high-frequency amplitude in the wavelets suggests that higher frequency radar might improve resolution only in the top few meters.

1.4 GHz radar penetration and evidence of drainage structures in temperate ice: Black Rapids Glacier, Alaska, U.S.A.

“…There is no phase polarity change upon transmission through an interface. Interpretation of dielectric contrasts from phase polarity changes is discussed more extensively by Arcone and others (1995) and Arcone (1996).…”

“…However, the unwanted backscatter (clutter), manifested as englacial diffractions and out-of-plane hyperbolic reflections seen within depth profiles recorded above 30 MHz (Blindow and Thyssen, 1986;Arcone and others, 1995), may mostly be responses to interesting features related to drainage and whose structure a higher-frequency radar might resolve. Given our present understanding of conduit dimensions (Holmlund, 1988), their resolution would require relatively wide bandwidths centered at frequencies above about 500 MHz (Arcone and others,1995;Arcone, 1996), for which the in situ wavelengths are about 0.34 m or less.…”

“…Consequently, their wide beamwidths (Arcone, 1995) reduce their performance because clutter suppression has an inverse dependence on antenna beamwidth (Skolnick, 1980). The penetration depth of short-pulse radars operating above 500 MHz and at necessarily low power has been limited to 530 m on polar glaciers (Glover and Rees, 1992;Arcone, 1996) and on temperate glaciers in late winter others, 1992, 1995). Although high frequencies (840 MHz) and also high-gain antennas (15 dB) have been employed with conventional, high-performance, modulated-carrier radioecho sounding systems to penetrate 750 m in ice (Narod and others, 1988), polar ice was profiled and much longer pulse durations were radiated.…”

Airborne fine-resolution UHF radar: an approach to the study of englacial reflections, firn compaction and ice attenuation rates

“…These data were collected aboard the Twin Otter during the 2009/10 Antarctic season. We assumed an average surface density of 0.7 kg m -3 (Blaisdell and others, 1992;Arcone, 1996) and an ice/water basal interface. We found the average attenuation rate to be 16.4 dB km -1 .…”

“…Arcone and Delaney (1987) and Arcone (1991) performed thickness measurements of river and lake ice using a helicopter-mounted short-pulse UHF radar, measuring ice thickness as small as 5-10 cm. Additional experiments have been conducted using modified existing radar systems (Fujita and others, 1999;Hempel and others, 2000), commercial off-the-shelf radar systems (Arcone, 1996(Arcone, , 2002Kohler and others, 1997;Arcone and others, 2005), vector network analyzer (VNA)-based radar systems (Richardson and others, 1997) and custom-built radar systems (Kanagaratnam andothers, 2001, 2004). The instrument described in this paper leverages the original work by Kanagaratnam and others (2004).…”