Geometric Power Fall-Off in Radar Sounding

Haynes, Mark; Chapin, Elaine; Schroeder, Dustin M.

doi:10.1109/tgrs.2018.2840511

Cited by 49 publications

(56 citation statements)

References 37 publications

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“…Bailey and others, 1964; Gudmandsen, 1969; Bamber and others, 2013; Fretwell and others, 2013). In the last two decades, the emphasis has expanded to the investigation of the geometric, thermal and material properties of the basal interface, by using the sounder-appropriate radar equation to solve for either basal reflectivity or echo character (Peters and others, 2005; Oswald and Gogineni, 2008; Schroeder and others, 2013; Grima and others, 2014b; Haynes and others, 2018b; Haynes, 2020).…”

Section: Ice Sheet and Glacier Bed Conditionsmentioning

confidence: 99%

“…Perhaps the most widely and successfully studied basal feature with radar sounding data has been subglacial water bodies, particularly subglacial lakes in Antarctica using the principle that subglacial water results in reflections brighter than surrounding bed echoes in radar data (Oswald and Robin, 1973; Peters and others, 2005; Wright and Siegert, 2012). Because of the coherent specular character of subglacial water, small fractional areas can dominate the echo both in terms of reflectivity and geometric spreading (Haynes and others, 2018b). This has been exploited to automatically detect lakes in radar sounding data (Carter and others, 2007; Ilisei and others, 2018).…”

Section: Ice Sheet and Glacier Bed Conditionsmentioning

confidence: 99%

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Five decades of radioglaciology

et al. 2020

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Radar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. As a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed. Terrestrially, airborne radar sounding has been used in glaciology to observe ice thickness, basal topography and englacial layers for five decades. More recently, radar sounding data have also been exploited to estimate the extent and configuration of subglacial water, the geometry of subglacial bedforms and the subglacial and englacial thermal states of ice sheets. Planetary radar sounders have observed, or are planned to observe, the subsurfaces and near-surfaces of Mars, Earth's Moon, comets and the icy moons of Jupiter. In this review paper, and the thematic issue of the Annals of Glaciology on ‘Five decades of radioglaciology’ to which it belongs, we present recent advances in the fields of radar systems, missions, signal processing, data analysis, modeling and scientific interpretation. Our review presents progress in these fields since the last radio-glaciological Annals of Glaciology issue of 2014, the context of their history and future prospects.

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Section: Ice Sheet and Glacier Bed Conditionsmentioning

confidence: 99%

Section: Ice Sheet and Glacier Bed Conditionsmentioning

confidence: 99%

Five decades of radioglaciology

et al. 2020

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“…Thin (~10 cm) section analyses from ice cores, while providing direct orientation estimates for the majority of grains within each section, are often conducted at depth intervals of tens of metres, with each analysis capturing the local decimetre-wide fabric regime, as is the case for the WAIS Divide deep ice core (WDC) at an average depth interval of 40 metres (Fitzpatrick et al, 2014). In contrast, waveform-based methods average out fabric properties in bulk where, for radar systems, the planar footprint of which the COF is averaged from is dependent on the radiation patterns of the radar antennas and increases linearly through depth, and can be approximated as the radius of the first Fresnel zone (Haynes et al, 2018). As the antennas used in this study have a relatively wide half-power beamwidth (±30 • ), the footprint of the ApRES system would have a radius of approximately 1/4 of the centre wavelength (~1 m) near the surface, but reaches to approximately 1000 m at a depth of 1500 m. Therefore, the bulk COF estimates obtained from ApRES is averaged from a much larger area at depth than near the surface.…”

Section: Methods Comparisons and Limitationsmentioning

confidence: 99%

Rapid and accurate polarimetric radar measurements of ice crystal fabric orientation at the Western Antarctic Ice Sheet (WAIS) Divide deep ice core site

Young¹,

Martín²,

Christoffersen³

et al. 2020

Preprint

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Abstract. The Crystal Orientation Fabric (COF) of ice sheets records the past history of ice sheet deformation and influences present-day ice flow dynamics. Though not widely implemented, coherent ice-penetrating radar is able to detect anisotropic COF patterns by exploiting the birefringence of ice crystals at radar frequencies. Most previous radar studies quantify COF at a coarse azimuthal resolution limited by the number of observations made with a pair of antennas along an acquisition plane that rotates around an azimuth centre. In this study, we instead conduct a suite of quad-polarimetric measurements consisting of four orthogonal antenna orientation combinations at the Western Antarctic Ice Sheet (WAIS) Divide Deep Ice Core site. From these measurements, we are able to quantify COF at this site to a depth of 1500 m at azimuthal and depth resolutions of up to 1° and 15 m. Our estimates of fabric asymmetry closely match corresponding fabric estimates directly measured from the WAIS Divide Deep Ice Core. While ice core studies are often unable to determine the absolute fabric orientation due to core rotation during extraction, we are able to unambiguously identify and conclude that the fabric orientation is depth-invariant to at least 1500 m, equivalent to 7400 years BP (years before 1950), and coincides exactly with the modern surface strain direction at WAIS Divide. Our results support the claim that the deformation regime at WAIS Divide has not changed substantially through the majority of the Holocene. Rapid polarimetric determination of bulk COF compares well with much more laborious sample-based COF measurements from thin ice sections. Because it is the former that ultimately influences ice flow, these polarimetric radar methods provide an opportunity for accurate and widespread mapping of bulk COF and its incorporation into ice flow models.

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“…As bed roughness increases, the radar pulse is scattered over a greater range of angles; this results in a 15 decrease in peak returned-power, and an increase in the trailing edge of the echo. The mathematical formulation of this relationship depends on the physical model for electromagnetic interference (phase coherence, or incoherence) and the statistical model for the subglacial interface (Berry, 1973;Peters et al, 2005;Haynes et al, 2018). The most commonly employed scattering model for the RES of glacier beds assumes phase-coherent interference, 'smoothly undulating' Gaussian statistics for rms roughness and radial isotropy (Berry, 1975;Peters et al, 2005;MacGregor et al, 2013;Grima et al, 2014;Schroeder 20 et al, 2015).…”

Section: Estimating Fine-scale Roughness and The 'Peakiness Index'mentioning

confidence: 99%

Subglacial roughness of the Greenland Ice Sheet: relationship with contemporary ice velocity and geology

Cooper¹,

Jordan²,

Schroeder³

et al. 2019

Preprint

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The subglacial environment of the Greenland Ice Sheet (GrIS) is poorly constrained, both in its bulk properties, for example geology, presence of sediment, and of water, and interfacial conditions, such as roughness and bed rheology.There is, therefore, limited understanding of how spatially heterogeneous subglacial properties relate to ice-sheet motion.Here, via analysis of two decades worth of radio-echo sounding data, we present a new systematic analysis of subglacial roughness beneath the GrIS. We use two independent methods to quantify subglacial roughness: first, the variability of along-5 track topography-enabling an assessment of roughness anisotropy from pairs of orthogonal transects aligned perpendicular and parallel to ice flow; and second, from bed-echo scattering-enabling assessment of fine-scale bed characteristics. We establish the spatial distribution of subglacial roughness and quantify its relationship with ice flow speed and direction. Overall, the beds of fast-flowing regions are observed to be rougher than the slow-flowing interior. Topographic roughness exhibits an exponential scaling relationship with ice surface velocity parallel, but not perpendicular, to flow direction in fast-flowing 10 regions, and the degree of anisotropy is correlated with ice surface speed. In many slow-flowing regions both roughness methods indicate spatially coherent regions of smooth bed, which, through combination with analyses of underlying geology, we conclude is likely due to the presence of a hard flat bed. Consequently, the study provides scope for a spatially variable hard bed/soft bed boundary constraint for ice-sheet models.

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Geometric Power Fall-Off in Radar Sounding

Cited by 49 publications

References 37 publications

Five decades of radioglaciology

Five decades of radioglaciology

Rapid and accurate polarimetric radar measurements of ice crystal fabric orientation at the Western Antarctic Ice Sheet (WAIS) Divide deep ice core site

Subglacial roughness of the Greenland Ice Sheet: relationship with contemporary ice velocity and geology

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