Abstract
ABSTRACTThe phase-sensitive radio-echo sounder (pRES) is a powerful new instrument that can measure the depth of internal layers and the glacier bed to millimetre accuracy. We use a stationary 16-antenna pRES array on Store Glacier in West Greenland to measure the three-dimensional orientation of dipping internal reflectors, extending the capabilities of pRES beyond conventional depth sounding. This novel technique portrays the effectiveness of pRES in deriving the orientation of dipping internal layers that may complement profiles obtained through other geophysical surveying methods. Deriving ice vertical strain rates from changes in layer depth as measured by a sequence of pRES observations assumes that the internal reflections come from vertically beneath the antenna. By revealing the orientation of internal reflectors and the potential deviation from nadir of their associated reflections, the use of an antenna array can correct this assumption. While the array configuration was able to resolve the geometry of englacial layers, the same configuration could not be used to accurately image the glacier bed. Here, we use simulations of the performance of different array geometries to identify configurations that can be tailored to study different types of basal geometry for future deployments.
Highlights
Over the last 50 years, the Greenland and Antarctic ice sheets have been extensively surveyed using radio echo sounding, allowing researchers to determine ice thickness and internal stratigraphy of these large ice bodies (e.g. Evans and Smith, 1969; Harrison, 1973; Robin and others, 1977; Drewry and Meldrum, 1978; Dahl-Jensen and others, 1997; Lythe and others, 2001; Paden and others, 2010; Bamber and others, 2013; Keisling and others, 2014; MacGregor and others, 2015) and revealing insights into their past and present flow dynamics (e.g. King and others, 2009; Sime and others, 2014; Bingham and others, 2015; MacGregor and others, 2015; Winter and others, 2015; Cavitte and others, 2016; Christianson and others, 2016)
While the majority of glaciological radar studies were conducted using airborne surveys or ground-based traverses, stationary phase-sensitive radio echo sounders have recently emerged as an important tool to measure one-dimensional (I-D) vertical strain on ice sheets (Kingslake and others, 2014; Nicholls and others, 2015; Kingslake and others, 2016) and basal melting on ice shelves (Corr and others, 2002; Jenkins and others, 2006; Dutrieux and others, 2014; Marsh and others, 2016) with both high accuracy and precision
Nicholls and others (2015) and Lok and others (2015) briefly described the potential of phase-sensitive radio echo sounders (pRES) to be deployed in an imaging mode using a multiple-input multiple-output (MIMO) array system, which has the capability to sequentially switch between up to eight transmitting (Tx) and receiving (Rx) antennas with the aim to image the basal topography of ice sheets
Summary
Over the last 50 years, the Greenland and Antarctic ice sheets have been extensively surveyed using radio echo sounding (radar), allowing researchers to determine ice thickness and internal stratigraphy of these large ice bodies (e.g. Evans and Smith, 1969; Harrison, 1973; Robin and others, 1977; Drewry and Meldrum, 1978; Dahl-Jensen and others, 1997; Lythe and others, 2001; Paden and others, 2010; Bamber and others, 2013; Keisling and others, 2014; MacGregor and others, 2015) and revealing insights into their past and present flow dynamics (e.g. King and others, 2009; Sime and others, 2014; Bingham and others, 2015; MacGregor and others, 2015; Winter and others, 2015; Cavitte and others, 2016; Christianson and others, 2016). A MIMO system involves the transmission and reception of its signals (and combinations thereof) from multiple transmitting and receiving antennas, arranged in such a way to create a gridded synthetic aperture from the midpoints of each virtual antenna pair. While previous studies have implemented synthetic aperture experiments to image englacial and subglacial waterways and geometries by manually moving the antenna across gridded points on the glacier surface (Walford and Harper, 1981; Kennett, 1989; Walford and Kennett, 1989), only recently have radars been able to successfully and instantaneously image the full 3-D subglacial topography using multiple antennas (Paden and others, 2010; Jezek and others, 2011; Wu and others, 2011). We highlight key array parameters to be considered in future pRES system deployments
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