Investigations of the form and flow of ice sheets and glaciers using radio-echo sounding

Abstract

Radio-echo sounding (RES), utilizing a variety of radio frequencies, was developed to allow glaciologists to measure the thickness of ice sheets and glaciers. We review the nature of electromagnetic wave propagation in ice and snow, including the permittivity of ice, signal attenuation and volume scattering, along with reflection from rough and specular surfaces. The variety of instruments used in RES of polar ice sheets and temperate glaciers is discussed. The applications and insights that a knowledge of ice thickness, and the wider nature of the form and flow of ice sheets, provides are also considered. The thickest ice measured is 4.7 km in East Antarctica. The morphology of the Antarctic and Greenland ice sheets, and many of the smaller ice caps and glaciers of the polar regions, has been investigated using RES. These findings are being used in three-dimensional numerical models of the response of the cryosphere to environmental change. In addition, the distribution and character of internal and basal reflectors within ice sheets contains information on, for example, ice-sheet layering and its chrono-stratigraphic significance, and has enabled the discovery and investigation of large lakes beneath the Antarctic Ice Sheet. Today, RES from ground-based and airborne platforms remains the most effective tool for measuring ice thickness and internal character.

Characteristics of Cherenkov radiation in naturally occurring ice

“…Below the firn R t = N t ⊥ /N t = 0.9975 at 9.7 GHz [29], similar to the value obtained at 39 GHz [30]. The results reported on the two refractive indices compare well with the standard value n = 3.18 [31] at radio frequencies referred to in ARIANNA papers. Ice crystal orientations are believed to play a significant role, and birefringence due to oriented ice crystals is significant.…”

Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites

“…Depths are measured from the surface, to which we apply firn corrections (z f ) of 13.60 m and 14.60 m at Vostok and Dome C, respectively. These corrections are computed using Eqn (1) below, following Dowdeswell and Evans (2004) and published vertical density profiles for each site (Lipenkov and others, 1997; Barnes and others, 2002).…”

Radio-frequency probes of Antarctic ice at South Pole

“…5, 6, and 7 show zooms of the reflections corresponding to the time intervals around 6 µs, 9.6 µs and 13.9 µs, illustrating the similarity of the reflection arrival time. We use these figures to also correlate our measurements with perhaps more familiar units of depth by translating reflection times to distances, using a temperature-weighted average EM wave velocity of 169±0.3 m/µs below the firn (Dowdeswell and Evans, 2004); through the firn, we use direct measurements of radio propagation wavespeed at South Pole (Kravchenko et al, 2005).…”