Inversion for the density‐depth profile of polar firn using a stepped‐frequency radar

Arthern, Robert; Corr, Hugh; Gillet-Chaulet, Fabien; Hawley, R. L.; Morris, Ε. M.

doi:10.1002/jgrf.20089

Cited by 21 publications

(24 citation statements)

References 35 publications

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“…A complementary approach is to exploit the density dependence of radio-wave propagation speed. The principle underlying the technique involves illuminating a reflector with different ray paths such that both the reflector depth and the radiowave propagation speed may be calculated using methods such as the Dix inversion (Dix, 1955), semblance analysis (e.g., Booth et al, 2010Booth et al, , 2011, interferometry (Arthern et al, 2013), or traveltime inversion based on ray tracing (Zelt and Smith, 1992;Brown et al, 2012).…”

Section: R Drews Et Al: Density From Wide-angle Radarmentioning

confidence: 99%

Constraining variable density of ice shelves using wide-angle radar measurements

Drews

Brown²,

Matsuoka

et al. 2016

The Cryosphere

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Abstract. The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium, for which knowledge of the depthaveraged density is essential. The densification from snow to ice depends on a number of local factors (e.g., temperature and surface mass balance) causing spatial and temporal variations in density-depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar data sets (10 MHz) collected at five sites on Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, Antarctica. We reconstruct depth to internal reflectors, local ice thickness, and firn-air content using a novel algorithm that includes traveltime inversion and ray tracing with a prescribed shape of the depthdensity relationship. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggest that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals that the firn inside the channel is 4.7 % denser than that outside the channel. Hydrostatic ice thickness calculations used for determining basal melt rates should account for the denser firn in ice-shelf channels. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

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Section: R Drews Et Al: Density From Wide-angle Radarmentioning

confidence: 99%

Constraining variable density of ice shelves using wide-angle radar measurements

Drews

Brown²,

Matsuoka

et al. 2016

The Cryosphere

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“…At the largest depths, the receiver is well below the firn layer at Summit, which is measured to be ∼100 m [1]. We compare these measurements to models of electromagnetic wave propagation through the firn to constrain possible radio propagation modes.…”

Section: Introductionmentioning

confidence: 99%

“…We therefore construct two [5,12,13], and a model based on radio echo data at Summit Station [1]. We fit a double exponential to all of the data shown, motivated by [14] and shown with the red line.…”

Section: Modeling Of Radio Propagation In the Firn At Summit Statmentioning

confidence: 99%

“…To compare with measurements, we construct two different firn models, based on a variety of measurements of the density profile, ρðzÞ, at and near Summit Station [1,5,12,13] to determine the index of refraction as a function of depth in meters (z) for the firn layer. The commonly used Herron-Langway parametrization of firn models has two density regimes, each of which is fit by an exponential subtracted from an offset [14].…”

Section: Modeling Of Radio Propagation In the Firn At Summit Statmentioning

confidence: 99%

“…However, in the ∼100 m or more below the upper surface of the ice, the snow at the surface slowly transitions from loose snow to glacial ice below in a region called the firn. This firn region represents a density gradient from that of loose snow to that of ice [1,2], corresponding to an index of refraction of n ≈ 1.35 for the snow near the surface to n ¼ 1.78 for bulk ice in the radio frequency range of interest for neutrino detection [3,4]. Furthermore, annual variations in the firn mean that the gradient is not perfectly smooth-there are known layers in the firn, especially evident near the surface [5].…”

Section: Introductionmentioning

confidence: 99%

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Measurements and modeling of near-surface radio propagation in glacial ice and implications for neutrino experiments

et al. 2018

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We present measurements of radio transmission in the ∼100 MHz range through a ∼100 m deep region below the surface of the ice at Summit Station, Greenland, called the firn. In the firn, the index of refraction changes due to the transition from snow at the surface to glacial ice below, affecting the propagation of radio signals in that region. We compare our observations to a finite-difference time-domain (FDTD) electromagnetic wave simulation, which supports the existence of three classes of propagation: a bulk propagation ray-bending mode that leads to so-called "shadowed" regions for certain geometries of transmission, a surface-wave mode induced by the ice/air interface, and an arbitrary-depth horizontal propagation mode that requires perturbations from a smooth density gradient. In the non-shadowed region, our measurements are consistent with the bulk propagation ray-bending mode both in timing and in amplitude. We also observe signals in the shadowed region, in conflict with a bulk-propagation-only ray-bending model, but consistent with FDTD simulations using a variety of firn models for Summit Station. The amplitude and timing of our measurements in all geometries are consistent with the predictions from FDTD simulations. In the shadowed region, the amplitude of the observed signals is consistent with a best-fit coupling fraction value of 2.4% (0.06% in power) or less to a surface or horizontal propagation mode from the bulk propagation mode. The relative amplitude of observable signals in the two regions is important for experiments that aim to detect radio emission from astrophysical high-energy neutrinos interacting in glacial ice, which rely on a radio propagation model to inform simulations and perform event reconstruction.

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Ice‐flow reorganization in West Antarctica 2.5 kyr ago dated using radar‐derived englacial flow velocities

Kingslake

Martín

Arthern

et al. 2016

Geophysical Research Letters

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We date a recent ice‐flow reorganization of an ice divide in the Weddell Sea Sector, West Antarctica, using a novel combination of inverse methods and ice‐penetrating radars. We invert for two‐dimensional ice flow within an ice divide from data collected with a phase‐sensitive ice‐penetrating radar while accounting for the effect of firn on radar propagation and ice flow. By comparing isochronal layers simulated using radar‐derived flow velocities with internal layers observed with an impulse radar, we show that the divide's internal structure is not in a steady state but underwent a disturbance, potentially implying a regional ice‐flow reorganization, 2.5 (1.8–2.9) kyr B.P. Our data are consistent with slow ice flow in this location before the reorganization and the ice divide subsequently remaining stationary. These findings increase our knowledge of the glacial history of a region that lacks dated constraints on late‐Holocene ice‐sheet retreat and provides a key target for models that reconstruct and predict ice‐sheet behavior.

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Inversion for the density‐depth profile of polar firn using a stepped‐frequency radar

Cited by 21 publications

References 35 publications

Constraining variable density of ice shelves using wide-angle radar measurements

Constraining variable density of ice shelves using wide-angle radar measurements

Measurements and modeling of near-surface radio propagation in glacial ice and implications for neutrino experiments

Ice‐flow reorganization in West Antarctica 2.5 kyr ago dated using radar‐derived englacial flow velocities

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