A ground-based radar for measuring vertical strain rates and time-varying basal melt rates in ice sheets and shelves

Nicholls, Keith W.; Corr, Hugh; Stewart, C.; Lok, Lai Bun; Brennan, Paul V.; Vaughan, David G.

doi:10.3189/2015jog15j073

Cited by 127 publications

(146 citation statements)

References 27 publications

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“…the difference between refreezing and melting. Point measurements with phase-sensitive radars (Marsh et al, 2016;Nicholls et al, 2015), global navigation satellite system (GNSS) receivers (Shean et al, 2017), observations from underwater vehicles (Dutrieux et al, 2014) and analysis from high-resolution satellites (Dutrieux et al, 2013;Wilson et al, 2017) have shown that BMB varies spatially on sub-kilometre scales. Ice shelf channels are one expression of localized basal melting (Stanton et al, 2013;Marsh et al, 2016) which, after hydrostatic adjustment, form curvilinear depressions visible at the ice shelf surface (Fig.…”

Section: S Berger Et Al: Spatial Variability Of Ice Shelf Basal Masmentioning

confidence: 99%

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Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

et al. 2017

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Abstract. Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e. the difference between refreezing and melting. Here, we present an improved technique -based on satellite observations -to capture the small-scale variability in the BMB of ice shelves. As a case study, we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica, and derive its yearly averaged BMB at 10 m horizontal gridding. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmosphericmodel surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from −14.7 to 8.6 m a −1 ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km × 1.3 km) lowers by 0.5 to 1.4 m a −1 , which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice shelf channels advect passively (i.e. no melting nor refreezing) toward the ice shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This study highlights expected challenges for a full coupling between ice and ocean models.

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Section: S Berger Et Al: Spatial Variability Of Ice Shelf Basal Masmentioning

confidence: 99%

“…Processing and acquisition schemes are as outlined previously (Nicholls et al, 2015;Marsh et al, 2016). The radar antennas were positioned at 22 sites.…”

Section: On-site Geophysical Measurementsmentioning

confidence: 99%

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

et al. 2017

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“…The pRES instrument operates over the frequency range 200-400 MHz and is centred at 300 MHz, which allows for sufficient ice penetration while its phase sensitivity allows it to achieve millimetre-depth precision. The design and technical details for the instrument's radar board are described in detail in Brennan and others (2014) and the practical aspects and limitations of its deployment in a quasi-monostatic (1 Tx/1 Rx) configuration are presented in Nicholls and others (2015). The MIMO array used in the field experiments consisted of two rows of antennas on the ice surface oriented orthogonal to each other ( Fig.…”

Section: Radar and Antenna Array Architecturementioning

confidence: 99%

“…While the majority of glaciological radar studies were conducted using airborne surveys or ground-based traverses, stationary phase-sensitive radio echo sounders (pRES) 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 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 (yielding up to 64 virtual antenna pairs) with the aim to image the basal topography of ice sheets. Similar to phased arrays, 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.…”

Section: Introductionmentioning

confidence: 99%

Resolving the internal and basal geometry of ice masses using imaging phase-sensitive radar

et al. 2018

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ABSTRACT. The 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.

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“…the lowermost 20% of the ice. Temperature measurements in boreholes in the upper ∼600 m of the ice column need 20 to be merged with measurements of the vertical velocity by phase-sensitive radar systems (e.g., Nicholls et al, 2015). Using those data sets with ice-flow modeling and the age-depth distribution extrapolated from the Dome Fuji ice core would provide better estimates of the age near the bed as well as the respective annual layer thickness, which constrains the applicability of currently available ice core analytics (Fischer et al, 2013).…”

Section: Implication For Ground-based Oldest Ice Surveysmentioning

confidence: 99%

Glaciological characteristics in the Dome Fuji region and new assessment for 1.5 Ma old ice

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Binder

Eagles

et al. 2017

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A ground-based radar for measuring vertical strain rates and time-varying basal melt rates in ice sheets and shelves

Cited by 127 publications

References 27 publications

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

Resolving the internal and basal geometry of ice masses using imaging phase-sensitive radar

Glaciological characteristics in the Dome Fuji region and new assessment for 1.5 Ma old ice

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