| 1. |
- Ingvander, Susanne, 1979-
(författare)
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Snow particle size investigations using digital image analysis - implications for ground observations and remote sensing of snow
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the past century climate warming has caused rapid changes in the Cryosphere. This has increased the need to accurately monitor rates of change in snow and ice in remote or sparsely populated areas where environmental observing capacity is limited. Monitoring snow cover requires understanding of the snow pack and the snow surface attributes. Snow particle size is an important parameter for characterization of snow pack properties. The size and shape of the snow particles affects the snow/air-ratio which in turn affect how energy is reflected on the snow surface. This governs the snow pack energy balance by changing the albedo or backscattering properties of the snow. Both the albedo and the snow particle size can be quantified by remote sensing. However, the snow particle size estimated by remote sensing, also called the optically equivalent particle size, represents only an approximation of the true or physical particle size of snow. Thus, there is demand for methods that relate both parameters and help to improve the interpretation of remote sensing data of snow at higher spatial and temporal scales. To address this demand the aim of this dissertation thesis is to improve existing sampling methods of the physical snow particle size to retrieve high-resolution, spatial and temporal data sets for validation of remote sensing data. A field sampling method based on object-oriented analysis of digital images was developed that allows measurements of various snow particle size parameters such as length, width, area, specific surface area and shape. The method generates a continuous snow particle size distribution that supports the detailed statistical characterization of a large number of samples. The results show its possibility to compare data from different existing methods. The sampling method was applied in field sites in Antarctica and in northern Sweden, to characterize the spatial variability in the physical snow particle size and to estimate correlations between various remote sensing products and the observed physical snow particle size. The results of the presented studies show that more detailed measurements of snow particle size in the field at higher temporal and spatial scales can improve the interpretation of active and passive satellite retrieved data.
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| 2. |
- Jansson, Peter, et al.
(författare)
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Editorial
- 2018
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Ingår i: Geografiska Annaler. - 0435-3676 .- 1468-0459. ; 100:1, s. 1-3
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Gusmeroli, Alessio, et al.
(författare)
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Twenty years of cold surface layer thinning at Storglaciaren, sub-Arctic Sweden, 1989-2009
- 2012
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 58:207, s. 3-10
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the changes in the thermal structure of the polythermal glacier Storglaciaren, northern Sweden, over the 20 year period 1989-2009 derived by comparing maps of the depth of the englacial transition between cold ice (permanently frozen) and temperate ice (which contains water inclusions). The maps are based on interpreted ice-penetrating radar surveys from 1989, 2001 and 2009. Complex thinning of the cold layer, first identified between 1989 and 2001, is still ongoing. A volume calculation shows that Storglaciaren has lost one-third of its cold surface layer volume in 20 years, with a mean thinning rate of 0.80 +/- 0.24 m a(-1). We suggest that the thinning of the cold layer at Storglaciaren is connected to the climatic warming experienced by sub-Arctic Scandinavia since the 1980s and we argue that repeated ice-penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate.
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| 4. |
- Gusmeroli, Alessio, et al.
(författare)
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Vertical distribution of water within the polythermal Storglaciären, Sweden
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115:F4, s. F04002-
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of water content and its distribution in polythermal glaciers is required to model their flow and thermal state. However, observ of water content variations with depth in polythermal glaciers are scarce. Water content can be estimated from radio wave speed because they depend on one another. We obtained continuous profiles of radio wave speed variations with depth from zero-offset radar profiles collected in boreholes approximately 80 m deep in the upper ablation area of Storglaciaren, northern Sweden. These profiles show that the microcrystalline water system in the temperate ice is relatively homogeneous. The overall hydrothermal structure at this location is composed of a 20 m thick upper layer of cold, water-free ice, underlain by a temperate ice layer whose average water content is 0.6% +/- 0.3%. These results are corroborated by surface radar and thermistor measurements, which show that the depth of the cold temperate transition is 21 m and the calculated water content at that transition is 0.6% +/- 0.1%. These findings imply that the whole temperate ice layer is from 3 to 4 times softer than the cold ice and, consequently, that realistic ice flow models of polythermal glaciers should include the effect of water content on viscosity.
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| 5. |
- Hedfors, Jim, et al.
(författare)
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Investigating the ratio of basal drag and driving stress in relation to bedrock topography during a melt season on Storglaciären, Sweden, using force budget analysis
- 2003
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Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 37:1, s. 263-268
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Tidskriftsartikel (refereegranskat)abstract
- We apply the force-budget technique using the isothermal block-flow model, on Storglacia« ren, Sweden, to investigate the ratio between basal drag and driving stress in relation to a bedrock ridge in the bed topography during a peak melt season. The input data consist of glacier surface velocities collected using differential global positioning system surveying of a stake net and geometry fromprevious radar soundings and digitized ice surface maps. The study focuses on the effects of transverse bedrock ridges upon basal stress conditions.The pattern of the calculated ratio of basal drag and driving stress shows a rhythmical position of relatively high and lowbasal drags onthe stoss and lee sides, respectively, of the bedrock thresholds. One of the zones of low basal drag corresponds to the location where the highest basal sliding rate has been measured previously by borehode deformation studies. This zone also aligns with the area where the drainage system is suggested to change from englacial to subglacial.
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| 6. |
- Lindbäck, Katrin, et al.
(författare)
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High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet
- 2014
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Ingår i: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 6:2, s. 331-338
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Tidskriftsartikel (refereegranskat)abstract
- We present ice thickness and bed topography maps with a high spatial resolution (250-500 m) of a land-terminating section of the Greenland Ice Sheet derived from ground-based and airborne radar surveys. The data have a total area of similar to 12 000 km(2) and cover the whole ablation area of the outlet glaciers of Isunnguata Sermia, Russell, Leverett, Orkendalen and Isorlersuup up to the long-term mass balance equilibrium line altitude at similar to 1600m above sea level. The bed topography shows highly variable subglacial trough systems, and the trough of Isunnguata Sermia Glacier is overdeepened and reaches an elevation of similar to 500m below sea level. The ice surface is smooth and only reflects the bedrock topography in a subtle way, resulting in a highly variable ice thickness. The southern part of our study area consists of higher bed elevations compared to the northern part. The compiled data sets of ground-based and airborne radar surveys cover one of the most studied regions of the Greenland Ice Sheet and can be valuable for detailed studies of ice sheet dynamics and hydrology. The combined data set is freely available at doi:10.1594/pangaea.830314.
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| 7. |
- Pettersson, Rickard, et al.
(författare)
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Spatial pattern and stability of the cold surface layer of Storglaciären, Sweden
- 2007
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 53:180, s. 99-109
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms controlling the spatial distribution and temporal fluctuations of the thermal structure in polythermal glaciers have, to date, been poorly investigated and are not fully understood. We have investigated the sensitivity of the cold surface layer thickness to different forcing parameters and the causes for an observed thinning of the cold surface layer on Storglaciären, northern Sweden, between 1989 and 2001 using a one-dimensional thermomechanical model and measurements of ice surface temperature, vertical velocity and net mass balance. Similarities between the spatial patterns of the cold surface layer, net mass balance and emergence velocity together with modelled high sensitivity to variations in emergence velocities suggest that the net ablation and vertical ice advection are the dominant forcing parameters. Results from transient model experiments suggest that the cold surface layer reaches a new equilibrium after a perturbation in the forcing within a few decades. No significant change in ice flow or mass balance has been observed at Storglaciären in recent decades. Instead, an increase of 1°C in winter air temperature since the mid-1980s is probably the cause of the observed thinning of the cold surface layer. Increased winter temperatures at the ice surface result in a reduced formation rate of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold-temperate transition surface. Model results indicate that the cold surface layer is more sensitive to changes in ice surface temperature in areas with lower emergence velocity, which explains the observed complex thinning pattern of the cold surface layer.
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| 8. |
- Ingvander, Susanne, et al.
(författare)
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Particle Size Sampling and Object-Oriented Image Analysis for Field Investigations of Snow Particle Size, Shape, and Distribution
- 2013
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Ingår i: Arctic, Antarctic and Alpine research. - : Informa UK Limited. - 1523-0430 .- 1938-4246. ; 45:3, s. 330-341
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Tidskriftsartikel (refereegranskat)abstract
- Snow particle size is an important parameter strongly affecting snow cover broadband albedo from seasonally snow covered areas and ice sheets. It is also important in remote sensing analyses because it influences the reflectance and scattering properties of the snow. We have developed a digital image processing method for the capture and analysis of data of snow particle size and shape. The method is suitable for quick and reliable data capture in the field. Traditional methods based on visual inspection of samples have been used but do not yield quantitative data. Our method provides an alternative to both simpler and more complex methods by providing a tool that limits the subjective effect of the visual analysis and provides a quantitative particle size distribution. The method involves image analysis software and field efficient instrumentation in order to develop a complete process-chain easily implemented under field conditions. The output from the analysis is a two-dimensional analysis of particle size, shape, and distributions for each sample. The results of the segmentation process were validated against manual delineation of snow particles. The developed method improves snow particle analysis because it is quantitative, reproducible, and applicable for different types of field sites.
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| 9. |
- Jansson, Peter, et al.
(författare)
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Ice sheet growth under dirty conditions : implications of debris cover for early glaciation advances
- 2002
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Ingår i: Quaternary International. - 1040-6182 .- 1873-4553. ; 95-96, s. 35-42
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Tidskriftsartikel (refereegranskat)abstract
- Debris-covered glaciers respond differently to any given set of climatic conditions than clean glaciers. This difference stems from change in ablation rate caused by a debris cover, approaching zero ablation with sufficiently thick protective cover, a mechanism not yet considered in the context of ice sheet growth. Critical to applying the mechanism to ice sheets is supply of debris. We postulate that periods after major interglacials offer the best conditions for dirty advances. This is because the volume of debris, previously deposited and weathered in interglacial time, the latter a function of exposure length, should be at a maximum. Advances of dirty ice sheets generate landforms and in positions deviating from clean-ice advances under similar climatic conditions. Hence, inferences of both ice sheet properties inferred from such dirty ice advances and the climate conditions related to such advances must be cautious. Furthermore, modeling of past ice sheets must consider the effect of debris cover whenever indications exist for such a cover.
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| 10. |
- Linderholm, Hans W., 1968, et al.
(författare)
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A high-resolution reconstruction of Storglaciären mass balance back to 1780/1781 using tree-ring data and circulation indices
- 2007
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Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 67, s. 12-20
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Tidskriftsartikel (refereegranskat)abstract
- Storglaciären in northernmost Sweden has the world’s longest ongoing continuous mass-balance record, starting in 1946. To extend this mass-balance record, we have reconstructed summer (bS) and winter (bW) mass balances separately back to the mass balance year 1780/81 with annual resolution. We used tree-ring data for bS and a set of circulation indices, based on the sea level pressure, for bW. Both proxies have correlation coefficients with respective mass balance components of ca. 0.7. The reconstructed net balance (bN) of Storglaciären was well correlated to the observations during 1946–1980 (r = 0.8, p<0.05). Our reconstruction agrees well with previously obtained results of northern Sweden glacier variability, where the predominantly positive bN years between 1890 and 1910 correspond to the well documented post-Little Ice Age advance of Storglaciären. Furthermore, the results suggest that bS, as a function of summer temperatures, is more important than bW in determining the bN, which is contrary to glaciers in the maritime parts of western Scandinavia. In general, bN has been negative over the last 220 yr, suggesting a predomination of continental conditions over northern Sweden. However, the influence of bW increased in the late twentieth century, indicating a shift to a more oceanic climate regime.
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