Assessment of CryoSat-2 interferometric and non-interferometric SAR altimetry over ice sheets

McMillan, Malcolm; Shepherd, A.; Muir, Alan; Gaudelli, Julia; Hogg, Anna E.; Cullen, R.

doi:10.1016/j.asr.2017.11.036

Cited by 9 publications

(5 citation statements)

References 38 publications

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“…From the Eulerian approach, we find that the main trunk of DG thinned at 0.4 ± 0.1 m/year between 2011 and 2013, with areas surrounding the glacier thickening at 0.35 ± 0.1 m/year (Figure c). This magnitude thinning is consistent with prior altimetry records (Flament & Rémy, ; McMillan et al, ) where thinning was also confined in the areas of fast flow. This signal suggests that ice flows faster than the speed required to maintain a state of mass balance.…”

Section: Resultssupporting

confidence: 91%

Grounding Line Retreat of Denman Glacier, East Antarctica, Measured With COSMO‐SkyMed Radar Interferometry Data

Brancato

Rignot

Milillo

et al. 2020

Geophysical Research Letters

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Denman Glacier, East Antarctica, holds an ice volume equivalent to a 1.5 m rise in global sea level. Using satellite radar interferometry from the COSMO-SkyMed constellation, we detect a 5.4 ± 0.3 km grounding line retreat between 1996 and 2017-2018. A novel reconstruction of the glacier bed topography indicates that the retreat proceeds on the western flank along a previously unknown 5 km wide, 1,800 m deep trough, deepening to 3,400 m below sea level. On the eastern flank, the grounding line is stabilized by a 10 km wide ridge. At tidal frequencies, the grounding line extends over a several kilometer-wide grounding zone, enabling warm ocean water to melt ice at critical locations for glacier stability. If warm, modified Circumpolar Deep Water reaches the sub-ice-shelf cavity and continues to melt ice at a rate exceeding balance conditions, the potential exists for Denman Glacier to retreat irreversibly into the deepest, marine-based basin in Antarctica. Plain Language SummaryUsing satellite radar data from the Italian COSMO-SkyMed constellation, we document the grounding line retreat of Denman Glacier, a major glacier in East Antarctica that holds an ice volume equivalent to a 1.5 m global sea level rise. The grounding line is retreating asymmetrically. On the eastern flank, the glacier is protected by a subglacial ridge. On the western flank, we find a deep and steep trough with a bed slope that makes the glacier conducive to rapid retreat. If warm water continues to induce high rates of ice melt near the glacier grounding zone, the potential exists for Denman Glacier to undergo a rapid and irreversible retreat, with major consequences for sea level rise.

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Section: Resultssupporting

confidence: 91%

Grounding Line Retreat of Denman Glacier, East Antarctica, Measured With COSMO‐SkyMed Radar Interferometry Data

Brancato

Rignot

Milillo

et al. 2020

Geophysical Research Letters

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“…Satellite-radar altimetry data are key in documenting the most recent changes in Earth's cryosphere [1][2][3][4][5][6][7][8][9]. Due to the radars' large beam-limited footprint (∼13 km in diameter), conventional radar altimetry has difficulties in mapping regions with highly varying surface relief.…”

Section: Introductionmentioning

confidence: 99%

Regional Assessments of Surface Ice Elevations from Swath-Processed CryoSat-2 SARIn Data

et al. 2021

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The Arctic responds rapidly to climate change, and the melting of land ice is a major contributor to the observed present-day sea-level rise. The coastal regions of these ice-covered areas are showing the most dramatic changes in the form of widespread thinning. Therefore, it is vital to improve the monitoring of these areas to help us better understand their contribution to present-day sea levels. In this study, we derive ice-surface elevations from the swath processing of CryoSat-2 SARIn data, and evaluate the results in several Arctic regions. In contrast to the conventional retracking of radar data, swath processing greatly enhances spatial coverage as it uses the majority of information in the radar waveform to create a swath of elevation measurements. However, detailed validation procedures for swath-processed data are important to assess the performance of the method. Therefore, a range of validation activities were carried out to evaluate the performance of the swath processor in four different regions in the Arctic. We assessed accuracy by investigating both intramission crossover elevation differences, and comparisons to independent elevation data. The validation data consisted of both air- and spaceborne laser altimetry, and airborne X-band radar data. There were varying elevation biases between CryoSat-2 and the validation datasets. The best agreement was found for CryoSat-2 and ICESat-2 over the Helheim region in June 2019. To test the stability of the swath processor, we applied two different coherence thresholds. The number of data points was increased by approximately 25% when decreasing the coherence threshold in the processor from 0.8 to 0.6. However, depending on the region, this came with the cost of an increase of 33–65% in standard deviation of the intramission differences. Our study highlights the importance of selecting an appropriate coherence threshold for the swath processor. Coherence threshold should be chosen on a case-specific basis depending on the need for enhanced spatial coverage or accuracy.

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“…Furthermore, due to AltiKa's 35-day repeat cycle, the track spacing is wider compared to CryoSat-2 and only half (48.1%) of grid cells falling on fast-flowing ice (v > 250 m/year) are surveyed. For comparison, the interferometric altimeter of CryoSat-2 is able to survey 92.7% of the same ice (McMillan et al, 2017).…”

Section: Comparison Between Ka-band Satellite Altimetry and Airborne Laser Altimetrymentioning

confidence: 99%

Ice Sheet Elevation Change in West Antarctica From Ka‐Band Satellite Radar Altimetry

Otosaka

Shepherd

McMillan

2019

Geophysical Research Letters

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Satellite altimetry has been used to track changes in ice sheet elevation using a series of Ku‐band radars in orbit since the late 1970s. Here, we produce an assessment of higher‐frequency Ka‐band satellite radar altimetry for the same purpose, using SARAL/AltiKa measurements recorded over West Antarctica. AltiKa elevations are 3.8 ± 0.5 and 2.5 ± 0.1 m higher than those determined from airborne laser altimetry and CryoSat‐2, respectively, likely due to the instruments' coarser footprint in the sloping coastal margins. However, AltiKa rates of elevation change computed between 2013 and 2019 are within 0.6 ± 2.4 and 0.1 ± 0.1 cm/year of airborne laser and CryoSat‐2, respectively, indicating that trends in radar penetration are negligible. The fast‐flowing trunks of the Pine Island and Thwaites Glaciers thinned by 117 ± 10 and 100 ± 20 cm/year, respectively, amounting to a 9% reduction and a 43% increase relative to the 2000s.

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Assessment of CryoSat-2 interferometric and non-interferometric SAR altimetry over ice sheets

Cited by 9 publications

References 38 publications

Grounding Line Retreat of Denman Glacier, East Antarctica, Measured With COSMO‐SkyMed Radar Interferometry Data

Grounding Line Retreat of Denman Glacier, East Antarctica, Measured With COSMO‐SkyMed Radar Interferometry Data

Regional Assessments of Surface Ice Elevations from Swath-Processed CryoSat-2 SARIn Data

Ice Sheet Elevation Change in West Antarctica From Ka‐Band Satellite Radar Altimetry

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