Trial lecture - time and place
Trial lecture: 10:15 am at Lille fysiske Auditorium (V232)
Adjudication committee
- Professor Bo Galle, Chalmers University of Technology, Gothenburg, Sweden
- Dr. Erna Frins, Physics Institute, Engineering School, Universidad de la Republica, Montevideo, Uruguay
- Professor Arne Dahlback, Department of Physics, University of Oslo, Norway
Chair of defence
Head of department Jøran Moen
Supervisors
- Dr. K. Stebel
- Dr. A. Kylling
- Dr. T. Skauli
- Prof. A. Sudbø
Additional information
This PhD thesis focuses on measurements of volcanic gas emissions and their impact on the environment and society, using optical remote sensing techniques. Particularly, the emissions of halogens (bromine and chlorine) and sulphur species are studied, which can have tremendous impact, both on local and global scales.
For the first time, the combined chemical evolution of reactive chlorine and bromine in the young emission plume of Mt. Etna in Italy is investigated, using the spectroscopic technique of Differential Optical Absorption Spectroscopy (DOAS). The measurements lead us to better understand the halogen chemistry of chlorine in volcanic plumes. We conclude, that the atmospheric impacts of volcanic chlorine emissions (e.g. ozone depletion) are less pronounced than their bromine equivalent, even though the bromine abundances in the plumes are orders of magnitude smaller.
The second part of the thesis focuses on the technique of UV SO2 cameras. The imaging devices can be used to measure the total volcanic emission-budget of the toxic pollutant sulphur dioxide (SO2) using ultraviolet (UV) sunlight as a light source. The open-source software Pyplis was developed which comprises a comprehensive collection of algorithms and routines relevant for the analysis of the image data in order to retrieve SO2-emission-rates. Pyplis aims to unify different analysis methods and has the vision to strive towards more transparency, more efficient analyses and the possibility to perform inter-comparison studies.
The retrieval of volcanic SO2-emission-rates requires knowledge of the gas velocities in the emission plume. These can be measured from the UV images directly using optical flow algorithms. Optical flow algorithms track contrast features in consecutive images and allow for velocity retrievals at the pixel-level. In a third study we address a common issue of such algorithms, namely that they cannot detect motion in homogeneous image areas. We show that this can lead to significant underestimations of the SO2-emission-rates. We propose a correction which is based on a local statistical analysis of a velocity field retrieved using an optical flow algorithm. Using two datasets from Mt. Etna, Italy and Guallatiri, Chile, we show that our correction for erroneous motion estimates works well and can significantly improve the robustness and reliability of the analysis. Furthermore, in this study we provide the first measurements of SO2-emission-rates from the volcano Guallatiri.