Univ., Diss.--Bremen, 2006. / Richtiger Name des Verf.: Nicolaus, Marcel.

The seasonal cycle of snow and sea ice is a fundamental feature of the Arctic climate system. In the Northern Hemisphere, about 55 million km2 of sea ice and snow undergo complete melt and freeze processes every year. Because snow and sea ice are much brighter (higher albedo) than the underlying surface, their presence reduces absorption of incoming solar energy at high latitudes. Therefore, changes of the sea-ice and snow cover have a large impact on the Arctic climate and possibly at lower latitudes. One of the most important determining factors of the seasonal snow and sea-ice cover is the timing of the seasonal melt-freeze transitions. Hence, in order to better understand Arctic climate variability, it is key to continuously monitor these transitions. This thesis presents an algorithm for obtaining melt-freeze transitions using scatterometers over both the land and sea-ice domains. These satellite-borne instruments emit radiation at microwave wavelengths and measure the returned signal. Several scatterometers are employed: QuikSCAT (1999–2009), ASCAT (2009–present), and OSCAT (2009–present). QuikSCAT and OSCAT operate at Ku-band (λ=2.2 cm) and ASCAT at C-band (λ=5.7 cm), resulting in slightly different surface interactions. This thesis discusses these dissimilarities over the Arctic sea-ice domain, and juxtaposes the time series of seasonal melt-freeze transitions from the three scatterometers and compares them with other, independent datasets. The interactions of snow and sea ice with other components of the Arctic climate system are complex. Models are commonly employed to disentangle these interactions. But this hinges upon robust and well-formulated models, reached by perpetual testing against observations. This thesis also presents an evaluation of how well eleven state-of-the-art global climate models reproduce the Arctic sea-ice cover and the summer length—given by the melt-freeze transitions—using surface observations of air temperature. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 4: Submitted.</p>

The aim of this diploma thesis is to monitor glacier change in the Cordillera Blanca in the period from 1987 to 2014. This diploma thesis focuses on three mountains and eleven glaciers in the northern part of the Cordillera Blanca. The input data consist of 29 Landsat scenes (Landsat 4,5,7 and 8) and the ASTER global digital elevation model version 2. Semi-automatic classification algorithm is created based on threshold values detected by spectral analyses of selected land cover types in the Cordillera Blanca. Additionally, the mean snowline (equilibrium line) altitude change is computed for all of the three mountains and eleven glaciers. Besides, glacier change depending on slope and aspect is evaluated. The results of this diploma thesis are presented in maps, tables and charts. The results of the classification are compared with the GLIMS Glacier Database and the field measurements provided by Adam Emmer, MSc. Finally, the advantages and disadvantages of the new Landsat 8 satellite sensor are discussed. Key words: Remote sensing, Landsat, classification, ice and snow detection, ELA, Cordillera Blanca

Wind power is one of the fastest growing production methods of electric energy. The expansion of wind power in Sweden are focused to northern counties. There are advantages as good wind conditions and large unexploited areas to build wind farms in the north, but there are also problems caused by the long winters. Due to the long periods of cold climate, ice and snow accumulation on blades are a safety risk, induces production losses and causes wear at wind turbine components. The commercial de-icing systems are not fulfilling the demands of being cost effective and are mainly focusing the heating to the leading edge. Therefore a new de-icing system based on infrared radiation has been investigated. This system is supposed to be placed at the wind turbine tower and de-ice one blade at a time. Experiments with this new de-icing system has been performed in small and full scale at a section of a real wind turbine blade. The experiments were carried out in facilities of Arctic Falls in Piteå. Different parameters as power demand of the heaters, distance between blade and heaters, wavelength of the radiation, influence by the surrounding temperature and total de-icing time were evaluated. Results showed that the largest impact of the efficiency and de-icing time were induced by the distance and width of the radiation spectrum for the heaters. Three types of filaments with different peaks of wavelengths were investigated and the most efficient de-icing was achieved when using a combination of heaters. Measurements of intensity together with de-icing experiments showed that the optimal distance from the blade was 1.5 m for heaters with standard reflectors. The main conclusion from the experiments with an infrared de-icing system is that it works. But not efficient enough to compete with the commercial systems of today even though it manage to de-ice the whole blade instead of just the leading edge. But this de-icing system has good potential if the heaters first of all are developed to radiate a more concentrated beam of radiation that is only focusing at the blades. The new method is estimated to be an lower investment due to that the techniques of infrared heaters are already well implemented in other areas. But more economic calculations has to be done to further motivate the work.