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The objective of this study was to investigate the radio echo sounding properties of Svalbard glaciers and to use these data to obtain information about the glaciological environment. Particular emphasis was placed on obtaining an understanding of the dielectric properties of the ice and reflecting boundaries present. These were then used to elucidate the physical processes causing them. First, a theoretical model, describing the dielectric properties of a wet bed, was developed. The ice/bed interface was then investigated using, as the primary data source, radar reflection coefficients. From these data inferences about the presence of water and/or debris, roughness of the interface and geographical trends were made. A number of geological divides were detected. Second, the dielectric properties of Svalbard ice were considered using i) radio echo sounding data on the bulk in situ radar absorption and ii) measurements made on the dielectric properties of a sample of Spitsbergen ice. Data were collected between 20 Hz and 100 kHz in the temperature range -2.5 to -44.0C . From these and other data deductions about the thermal regime of the ice masses were made and a geographical trend, linked to the reflection coefficients, observed. The theory of dielectric absorption in ice was discussed with an emphasis on the high frequency, radio echo sounding characteristics. Third, the properties of an extraordinary internal reflecting horizon ( observed on 60% of the glaciers sounded in 1983) were investigated. A model was developed to describe the scattering properties of inhomogeneities ( of arbitrary size) within ice. Using this, and data on the re:flec~ing properties of the horizons, they were attributed to the presence of a finite quantity of water. The implications of this finding were considered. Finally, the surface and, where available, bedrock profiles of 40 glaciers and six ice caps, in Spitsbergen, were presented.

A high-resolution radio echo sounder operating at a frequency of 840 MHz has been developed for sounding of small and medium-sized polar glaciers and ice caps. The sounder uses a compact, high-gain antenna which improves the system performance, suppresses valley wall echoes and simplifies operation from light aircraft. Successful field trials were carried out on the Rusty, Trapridge and Hazard Glaciers, Yukon Territory, Canada. Results of airborne surveys compare well with ice depths obtained from earlier ground-based soundings on the Rusty and Trapridge Glaciers. The maximum ice thickness encountered was 200 m on Hazard Glacier. Owing to the high operating frequency, random scattering from inhomogeneities within the ice is a major cause of signal degradation. For this reason the sounder cannot penetrate great thicknesses of temperate or debris-rich ice. Spatial averaging, an immediate result of operating from a moving platform, reduces the effects of back-scattered "clutter. " Results of ground-based tests on the Hazard Glacier yield a value for ftan 8 = 0.26 at -50C, in agreement with predicted values. The total received power and the echo details have both been found to be very sensitive to small (<<I0 cm) changes in antennae position. Large fluctuations in power, caused by roughness at or near the ice/air surface, prevented using single coverage data to detect birefringence in glacier ice. The results also indicate that the standard photographic records should be replaced by a recording medium capable of storing more precise and accessible data. A storage medium such as magnetic tape should not degrade the radar data, and would at the same time relieve a data processing burden. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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No description available.

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Problemformulering och syfte: Internetaktivisten Eli Pariser berättar i sin bok The Filter Bubble: What the Internet Is Hiding from You hur algoritmer på sociala medier filtrerar bort innehåll som går emot det användaren tycker om. I stället får användaren ett skräddarsytt flöde som bara presenterar innehåll som går ihop med dennes personliga preferenser. Pariser argumenterar vidare att filtreringen skapar en filterbubbla, där användaren får uppfattningen att alla har samma åsikter som den själv. Det kan, enligt Pariser, leda till åsiktspolarisering där människor kommer allt längre ifrån varandra. Syftet med den här studien är att ta reda på hur unga, politiskt aktiva människor i Sverige använder Facebook och hur de upplever sina flöden på Facebook i förhållande till sina politiska åsikter, för att se hur utbrett internetfenomen som filterbubblan är bland svenska användare som tydligt ger uttryck för sina politiska åsikter. Metod och material: Metoden som ligger till grund för studiens empiriska resultat är en enkätundersökning. Analysenheterna består av politiskt aktiva Facebook-användare som är medlemmar i politiska ungdomsförbund. Anledningen till att medlemmar i ungdomsförbund valdes framför politiska partier är att yngre människor är mer aktiva på sociala medier. Enkäten utformades med tjänsten Survey monkey och spreds på Facebook till analysenheterna. Huvudresultat: Studiens empiriska resultat visar att majoriteten av respondenterna befinner sig något som Eli Pariser skulle definiera som en filterbubbla, men att de flesta samtidigt är medvetna om att åsiktsbilden i Facebook-flödet inte är representativt för det svenska samhället i stort.