Multisensor validation of tidewater glacier flow fields derived from
SAR intensity tracking

Rohner, Christoph; Small, David; Henke, Daniel; Lüthi, Martin P.; Vieli, Andreas

doi:10.5194/tc-2018-278

Cited by 3 publications

(6 citation statements)

References 23 publications

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“…The surface structure of these two distinct parts clearly reflects the dynamics of ice: the fast part is highly crevassed and steep (as observed at Farquhar glacier) while the immobile part is nearly flat (Figure 2). The spatial pattern of the velocity field is similar to those derived from UAV surveys in August 2016 by Rohner et al (2019) and Walter et al (2019). It is likely that the velocity field presented here is representative of the flow of Eqip Sermia after 2014, when its terminus has accelerated up 10-15 m d −1 .…”

Section: Ice Flow Velocitiessupporting

confidence: 71%

“…The substantial extension of the crack on July 8 suggests that it propagated step-wise before to collapse. and show smooth pattern of the ice dynamics as in Figure 7 or in a former UAV-inferred velocity field (Rohner et al, 2019;Walter et al, 2019). By contrast, the velocity field of the glacier front is spatially more erratic and varies greatly between the two flights (i.e., within 5 h).…”

Section: Short-term Ice Flow and Strain Rate Fields At Eqip Sermiamentioning

confidence: 76%

“…The approach presented in this study has potential to quantify iceberg calving of all sizes and/or measure the short-term variability of surface flow fields in complementary manner to existing observational methods, such as terrestrial time-lapse photogrammetry (e.g., Rosenau et al, 2013;James et al, 2014;Murray et al, 2015), radar interferometry (e.g., Walter et al, 2019), in-situ GPS and seismic measurements (e.g., Bassis and Jacobs, 2013), or remote sensing (e.g., Joughin and MacAyeal, 2005;Rohner et al, 2019). It would have been possible to infer sub-hour ice flow velocity fields at Eqip Sermia by flying twice as low to the surface (or equivalently halving the GSD).…”

Section: Discussionmentioning

confidence: 99%

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High-Endurance UAV for Monitoring Calving Glaciers: Application to the Inglefield Bredning and Eqip Sermia, Greenland

et al. 2019

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Unmanned aerial vehicle (UAV) photogrammetry has become an important tool for generating multi-temporal, high-resolution ortho-images and digital elevation models (DEMs) to study glaciers and their dynamics. In polar regions, the roughness of the terrain, strong katabatic winds, unreliability of compass readings, and inaccessibility due to lack of infrastructure pose unique challenges for UAV surveying. To overcome these issues, we developed an open-source, low-cost, high-endurance, fixed-wing UAV equipped with GPS post-processed kinematic for the monitoring of ice dynamics and calving activity at several remote tidewater glaciers located in Greenland. Our custom-built UAV is capable of flying for up to 3 h or 180 km and is able to produce high spatial resolution (0.25-0.5 m per pixel), accurately geo-referenced (1-2 pixels) ortho-images and DEMs. We used our UAV to perform repeat surveys of six calving glacier termini in north-west in July 2017 and of Eqip Sermia glacier, west Greenland, in July 2018. The endurance of our UAV enabled us to map the termini of up to four tidewater glaciers in one flight and to infer the displacement and calving activity of Eqip Sermia at short (105 min) timescale. Our study sheds light on the potential of long-range UAVs for continuously monitoring marine-terminating glaciers, enabling short-term processes, such as the tidal effects on the ice dynamics, short-lived speed-up events, and the ice fracturing responsible for calving to be investigated at unprecedented resolution.

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Section: Ice Flow Velocitiessupporting

confidence: 71%

Section: Short-term Ice Flow and Strain Rate Fields At Eqip Sermiamentioning

confidence: 76%

Section: Discussionmentioning

confidence: 99%

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High-Endurance UAV for Monitoring Calving Glaciers: Application to the Inglefield Bredning and Eqip Sermia, Greenland

et al. 2019

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“…Ice flow velocities from TRI data in vicinity of the calving front are presented in Figure 3a. Due to radar shadow, additionally Figure 3b has been created from a high resolution velocity field from repeated UAV surveys from August 2016 (Rohner et al 2019). Speeds are increasing towards the calving front with highest values of 16 m day -1 .…”

Section: Flow Velocitiesmentioning

confidence: 99%

Calving event size measurements and statistics of Eqip Sermia, Greenland, from terrestrial radar interferometry

Walter¹,

Lüthi²,

Vieli³

2019

Preprint

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Abstract. Calving is a crucial process for the recently observed dynamic mass loss changes of the Greenland ice sheet. Despite its importance for global sea level change, major limitations in understanding the calving process remain. This study presents calving event data and statistics recorded with a terrestrial radar interferometer at the front of Eqip Sermia, a marine terminating outlet glacier in Greenland. The data with a spatial resolution of several meters recorded at one-minute intervals was processed to provide source areas and volumes of 1700 individual calving events during a 6 day period. The calving front can be divided into sectors ending in shallow and deep water with different calving statistics and style. For the shallow sector, characterised by an inclined and very high front, calving events are more frequent and larger than for the vertical ice cliff of the deep sector. We suggest that the calving volume missing in our observations of the deep sector is removed by oceanic melt and subaquatic calving, which implies that subaqueous mass loss must be substantial for this sector with a contribution of up to 75 % to the frontal mass loss. The size distribution of the deep sector follows a power law, while the shallow sector is likely represented by a log-normal model. Variations in calving activity and style within the sectors seem to be controlled by the bed topography and the front geometry. Within the short observation period no clear relationship between environmental forcings and calving frequency or event volume could be detected.

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“…16 Ln 10: ". Left uncorrected, these introduce biases in the estimated magnitude of surface velocities (Nagler et al, 2015). ".…”

mentioning

confidence: 99%

Review of: Multisensor validation of tidewater glacier flow fields derived from SAR intensity tracking, by: Rohner et al. for The Cryosphere (tc-2018-278)

Anonymous

2019

Preprint

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Rohner et al. present a detailed validation study of ice velocity measurements derived from intensity feature tracking using Sentinel-1A and RADARSAT-2 SAR images. The study area is a tide-water glacier in Western Greenland (Eqip Sermia) which showed substantial fluctuations in recent years. The derived velocity maps are compared with field data, derived from 3 GPS stations, a Terrestrial Radar Interferometer (TRI) and repeated UAV surveys, in an effort to demonstrate the accuracy and limits of the method and data sets. Statistics are provided of the outcomes and are visualised in histograms, scatter plots and difference maps. The authors report a good agreement with the in-situ data with minor differences near the calving front ascribed to the characteristics of the different techniques. The ice velocity maps are also compared with Greenland-wide C1 * Pg. 9 Ln 8: "which corresponds to an area of about 25×25 m." Considering the chosen template size used for the tracking it actually corresponds to a much larger C3 TCD Interactive commentPrinter-friendly version Discussion paper area. * Pg. 16 Ln 10: ". Left uncorrected, these introduce biases in the estimated magnitude of surface velocities (Nagler et al., 2015). ". Did the authors apply any such corrections? If not, what is the estimated bias introduced by this? * Section 4.2: A large part of the discussion concerns an intercomparison of an annually averaged version of the '5m' maps with products from MEaSUREs and CCI. The authors find substantial differences near the calving front and margins but also further upstream. These differences are reported as an underestimation of ice flow in the operational products and according to the authors this implies an underestimation of ice fluxes and an overestimation of Greenland mass loss when used for mass balance assessments. These claims are, however, unsubstantiated by the current work for a number of reasons, aside from the issue regarding resolution described before.

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Multisensor validation of tidewater glacier flow fields derived from SAR intensity tracking

Cited by 3 publications

References 23 publications

High-Endurance UAV for Monitoring Calving Glaciers: Application to the Inglefield Bredning and Eqip Sermia, Greenland

High-Endurance UAV for Monitoring Calving Glaciers: Application to the Inglefield Bredning and Eqip Sermia, Greenland

Calving event size measurements and statistics of Eqip Sermia, Greenland, from terrestrial radar interferometry

Review of: Multisensor validation of tidewater glacier flow fields derived from SAR intensity tracking, by: Rohner et al. for The Cryosphere (tc-2018-278)

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