Sea‐ice thickness from airborne laser altimetry over the Arctic Ocean north of Greenland

Hvidegaard, Sine Munk; Forsberg, R.

doi:10.1029/2001gl014474

Cited by 37 publications

(32 citation statements)

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“…Then, the freeboard of the ice can be estimated, and can be used as a measure of ice thickness (Hvidegaard & Forsberg, 2002). The estimation of ice thickness from airborne or satellite altimetric measurements of freeboard will be discussed in the next section.…”

Section: Electromagnetic Induction Soundingmentioning

confidence: 99%

Dynamics versus Thermodynamics: The Sea Ice Thickness Distribution

Haas

2003

Sea Ice

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Changes of sea ice coverage are commonly taken as an indicator for climate change. Since 30 years, the area of the Arctic and Southern oceans covered by sea ice is routinely monitored by satellite radiometers (Chapter 6). These observations show that the ice coverage of the Arctic Ocean strongly declines during summer, with an average rate of -11.1% per decade. However, in 2007 and 2008, this trend was drastically exceeded when sea ice extent reduced to record lows of only 4.13 and 4.52 km 2 , less than 20% of previous summers, and raising concerns that the Arctic Ocean might become ice-free during summers within the next few decades. However, winter ice coverage of the Arctic Ocean decreases at a much slower pace of only -2.8% per decade. And in contrast to the Arctic, sea ice coverage of the Southern Ocean increases slightly, with 0.6% and 3.4% per decade in the winter and summer, respectively.The sea ice decline in the Arctic is much more rapid than predicted by any of the Intergovernmental Panel for Climate Change (IPCC) climate models . This demonstrates our limited understanding of the processes of sea ice growth and melt, and ice motion and deformation. For a full understanding of the areal changes, additional information on ice thickness is required, but is largely missing up to the date of this writing. This chapter will discuss the importance of ice thickness information, the most frequently used ice thickness measurement techniques and results from observations of long-term, interannual and seasonal thickness variations.In Chapter 2, it was described how sea ice initially forms from open water and subsequently grows into an ice cover, or in other terms, how sea ice grows thermodynamically. One of the basic concepts is that the more the ice grows thicker, the colder the air is due to the establishment of greater temperature gradients in the ice, and higher freezing rates. Vice versa, it would follow that as a consequence of climate warming, the polar sea ice cover would become thinner. However, another process contributes to the sea ice thickness distribution: Due to its relative thinness -some decimetres to a few metres -sea ice fl oating over deep water is subject to winds and currents which steadily move the ice around, i.e. the ice cover drifts. As a result, it breaks up into fl oes interspersed by open water leads. With changing drift directions and speeds, the ice fl oes will be pushed together and collide with each other. If the resulting forces in the ice become too large, it will fi nally break. The resulting

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Section: Electromagnetic Induction Soundingmentioning

confidence: 99%

Dynamics versus Thermodynamics: The Sea Ice Thickness Distribution

Haas

2003

Sea Ice

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“…However, before the R-value can be determined, snowfreeboard needs to be derived from the combined GPS/laser measurements. Hvidegaard and Forsberg [2002] developed a method for deriving snow-freeboard from airborne laser altimetry if it is combined with precise GPS. In this work a similar method was applied.…”

Section: Methodsmentioning

confidence: 99%

“…But it has, as the laser range accuracy, no effect on the measurements since snow-freeboard is derived from relative rather than from the absolute measurements. Earlier, the use of the Arctic geoid model was mentioned with respect to the method developed by Hvidegaard and Forsberg [2002]. According to Forsberg et al [2007], the Arctic geoid is accurate to better than 10 cm for most of the region.…”

Section: Accuracymentioning

confidence: 99%

“…The bottom curve is the ground elevation, the difference between the GPS height and laser height. Since the GPS and laser measurements are affected in the same way by the vertical helicopter motion, subtraction removes it [Hvidegaard and Forsberg, 2002].…”

Section: Retrieval Of Snow-freeboardmentioning

confidence: 99%

“…To categorize the factors, they used snow depths based on field experiments in the 1960s. Hvidegaard and Forsberg [2002] measured snow-freeboard with an airborne laser scanner and derived total thickness by multiplying snow-freeboard by a factor based on those of Wadhams et al [1992]. Laxon et al [2003] used measurements of icefreeboard from radar altimeters carried on the ERS-1 and ERS-2 satellites to derive total thickness, whereas Kwok and Cunningham [2008] and Zwally et al [2008] estimated total thickness from snow-freeboard retrieved from the ICESat satellite.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of coincident snow-freeboard and sea ice thickness profiles derived from helicopter-borne laser altimetry and electromagnetic induction sounding

Goebell

2011

J. Geophys. Res.

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[1] Sea ice thickness plays a critical role in global climate change, but it cannot be measured directly from space. Alternatively, sea ice freeboard is measured and converted to sea ice thickness with assumptions made for snow depth and snow/ice densities. This paper investigates the relationship between snow-freeboard (ice-freeboard plus snow) and total thickness (ice thickness plus snow) and addresses the uncertainties that arise from the unknown snow depth and snow/ice densities. A unique data set of coincident measurements of snow-freeboard and total thickness was collected in the Arctic and Antarctic. Snow-freeboard was determined by laser altimetry, and total thickness was determined by electromagnetic induction with a helicopter-borne instrument. Obtained total thickness/snow-freeboard ratios range from 2 to 12 in the Arctic and from 2 to 8 in the Antarctic. The principal finding is that the ratios vary greatly within each region, and a fixed ratio per profile should not be used, as this can induce incorrect ice thicknesses. The ratio uncertainties can induce a relative thickness error of 5.4% and 4.9% in the first-year and multiyear ice mode. Additionally, the coincident measurements allow the calculation of snow depth that can be used to densify existing in situ measurements. To assess accuracy, calculated snow depths were compared to in situ measurements and agree within ±5 cm. This increases if measurements and calculations differ spatially. The method of deriving snow-freeboard from laser altimetry is briefly described, and the variability of the total thickness/snow-freeboard ratio is shown for one profile in the Lincoln Sea and one in the Weddell Sea.Citation: Goebell, S. (2011), Comparison of coincident snow-freeboard and sea ice thickness profiles derived from helicopterborne laser altimetry and electromagnetic induction sounding,

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Contribution of Deformation to Sea Ice Mass Balance: A Case Study From an N‐ICE2015 Storm

Itkin

Spreen

Hvidegaard

et al. 2018

Geophysical Research Letters

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The fastest and most efficient process of gaining sea ice volume is through the mechanical redistribution of mass as a consequence of deformation events. During the ice growth season divergent motion produces leads where new ice grows thermodynamically, while convergent motion fractures the ice and either piles the resultant ice blocks into ridges or rafts one floe under the other. Here we present an exceptionally detailed airborne data set from a 9 km2 area of first year and second year ice in the Transpolar Drift north of Svalbard that allowed us to estimate the redistribution of mass from an observed deformation event. To achieve this level of detail we analyzed changes in sea ice freeboard acquired from two airborne laser scanner surveys just before and right after a deformation event brought on by a passing low‐pressure system. A linear regression model based on divergence during this storm can explain 64% of freeboard variability. Over the survey region we estimated that about 1.3% of level sea ice volume was pressed together into deformed ice and the new ice formed in leads in a week after the deformation event would increase the sea ice volume by 0.5%. As the region is impacted by about 15 storms each winter, a simple linear extrapolation would result in about 7% volume increase and 20% deformed ice fraction at the end of the season.

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Sea‐ice thickness from airborne laser altimetry over the Arctic Ocean north of Greenland

Cited by 37 publications

References 11 publications

Dynamics versus Thermodynamics: The Sea Ice Thickness Distribution

Dynamics versus Thermodynamics: The Sea Ice Thickness Distribution

Comparison of coincident snow-freeboard and sea ice thickness profiles derived from helicopter-borne laser altimetry and electromagnetic induction sounding

Contribution of Deformation to Sea Ice Mass Balance: A Case Study From an N‐ICE2015 Storm

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