Bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica

Gogineni, S.; Yan, Jiahao; Paden, John; Leuschen, Carl; Li, Jilu; Rodriguez‐Morales, Fernando; Braaten, D.; Purdon, K.; Wang, Z.; Liu, Weibo; Gauch, John M.

doi:10.3189/2014jog14j129

Cited by 65 publications

(59 citation statements)

References 48 publications

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“…However, this temperate, fast-flowing glacier is one of the most difficult targets to sound [65]. Figure 10 shows an echogram from the TO measurements over Jacobshavn Isbrae using the Band 2 mode.…”

Section: Twin Otter Results From the Jakobshavn Isbraementioning

confidence: 99%

“…These results strongly suggest the potential to further improve the HF sounder data if a cross-track array is synthesized. This 2D array synthesis could reduce off-angle clutter in areas where clutter is known to be the limiting factor [65]. Various configurations of CReSIS MCoRDS radar have been flown over Jakobshavn during field campaigns since the 1990s.…”

Section: Twin Otter Results From the Jakobshavn Isbraementioning

confidence: 99%

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HF/VHF Radar Sounding of Ice from Manned and Unmanned Airborne Platforms

et al. 2018

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Ice thickness and bed topography of fast-flowing outlet glaciers are large sources of uncertainty for the current ice sheet models used to predict future contributions to sea-level rise. Due to a lack of coverage and difficulty in sounding and imaging with ice-penetrating radars, these regions remain poorly constrained in models. Increases in off-nadir scattering due to the highly crevassed surfaces, volumetric scattering (due to debris and/or pockets of liquid water), and signal attenuation (due to warmer ice near the bottom) are all impediments in detecting bed-echoes. A set of high-frequency (HF)/very high-frequency (VHF) radars operating at 14 MHz and 30-35 MHz were developed at the University of Kansas to sound temperate ice and outlet glaciers. We have deployed these radars on a small unmanned aircraft system (UAS) and a DHC-6 Twin Otter. For both installations, the system utilized a dipole antenna oriented in the cross-track direction, providing some performance advantages over other temperate ice sounders operating at lower frequencies. In this paper, we describe the platform-sensor systems, field operations, data-processing techniques, and preliminary results. We also compare our results with data from other ice-sounding radars that operate at frequencies both above (Center for Remote Sensing of Ice Sheets (CReSIS) Multichannel Coherent Depth Sounder (MCoRDS)) and below (Jet Propulsion Laboratory (JPL) Warm Ice Sounding Explorer (WISE)) our HF/VHF system. During field campaigns, both unmanned and manned platforms flew closely spaced parallel and repeat flight lines. We examine these data sets to determine image coherency between flight lines and discuss the feasibility of forming 2D synthetic apertures by using such a mission approach.

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Section: Twin Otter Results From the Jakobshavn Isbraementioning

confidence: 99%

Section: Twin Otter Results From the Jakobshavn Isbraementioning

confidence: 99%

HF/VHF Radar Sounding of Ice from Manned and Unmanned Airborne Platforms

et al. 2018

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“…Soundings of ice thickness are made by airborne radar in the form of discrete radar flightlines, mostly running normal to the dominant ice flow direction. These can have high observational uncertainty in topographically complex regions (Gogineni et al, 2014).…”

Section: Characterization and Datamentioning

confidence: 99%

Bayesian Inference of Subglacial Topography Using Mass Conservation

2016

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We develop a Bayesian model for estimating ice thickness given sparse observations coupled with estimates of surface mass balance, surface elevation change, and surface velocity. These fields are related through mass conservation. We use the Metropolis-Hastings algorithm to sample from the posterior probability distribution of ice thickness for three cases: a synthetic mountain glacier, Storglaciären, and Jakobshavn Isbrae. Use of continuity in interpolation improves thickness estimates where relative velocity and surface mass balance errors are small, a condition difficult to maintain in regions of slow flow and surface mass balance near zero. Estimates of thickness uncertainty depend sensitively on spatial correlation. When this structure is known, we suggest a thickness measurement spacing of one to two times the correlation length to take best advantage of continuity based interpolation techniques. To determine ideal measurement spacing, the structure of spatial correlation must be better quantified.

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“…We use a one-dimensional along-flow bed topography profile in the deep trough and fjord as it is presented in Boghosian et al (2015). The fjord bathymetry is thereby obtained from Operation IceBridge gravity data, whereas the profile from high-sensitivity radar data by Gogineni et al (2014) at the present-day sea level from topography data and satellite images in the ice-free fjord (Fig. 1).…”

Section: Initializationmentioning

confidence: 99%

Non-linear retreat of Jakobshavn Isbræ since the Little Ice Age controlled by geometry

Steiger¹,

Nisancioglu²,

Åkesson³

et al. 2017

Preprint

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Abstract. Rapid acceleration and retreat of Greenland's marine-terminating glaciers during the last two decades have initiated questions on the trigger and processes governing observed changes. Destabilization of these glaciers coincides with atmosphere and ocean warming, which broadly has been used to explain the rapid changes. To assess the relative role of external forcing versus fjord geometry, we investigate the retreat of Jakobshavn Isbrae in West Greenland, where margin positions exist since the Little Ice Age maximum in 1850. We use a one-dimensional ice flow model and isolate geometric effects on the retreat 5 using a linear increase in external forcing.We find that the observed retreat of 43 km from 1850 until 2014 can only be simulated when multiple forcing parameterssuch as hydrofracturing, submarine melt and frontal buttressing by sea ice-are changed simultaneously. Surface mass balance, in contrast, has a negligible effect. While changing external forcing initiates retreat, fjord geometry controls the retreat pattern.Basal and lateral topography govern shifts from temporary stabilization to rapid retreat, resulting in a highly non-linear glacier 10 response. For example, we simulate a disintegration of a 15 km long floating tongue within one model year, which dislodges the grounding line onto the next pinning point. The retreat pattern loses complexity and becomes linear when we artificially straighten the glacier walls and bed, confirming the topographic controls.For real complex fjord systems such as Jakobshavn Isbrae, geometric pinning points predetermine grounding line stabilization and may therefore be used as a proxy for moraine build-up. Also, we find that after decades of stability and with constant 15 external forcing, grounding lines may retreat rapidly without any trigger. This means that past changes may precondition marine-terminating glaciers to reach tipping-points, and that retreat can occur without additional climate warming. Present-day changes and future projections can therefore not be viewed in isolation of historic retreat.

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Bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica

Cited by 65 publications

References 48 publications

HF/VHF Radar Sounding of Ice from Manned and Unmanned Airborne Platforms

HF/VHF Radar Sounding of Ice from Manned and Unmanned Airborne Platforms

Bayesian Inference of Subglacial Topography Using Mass Conservation

Non-linear retreat of Jakobshavn Isbræ since the Little Ice Age controlled by geometry

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