The PhD defense of Johannes Lohse takes place on March 11-12

Johannes Lohse will publically defend his thesis for the PhD degree in Science on «On Automated Classification of Sea Ice Types in SAR Imagery» on Friday March 12 at 14:15.

The trial lecture on «Atmospheric and oceanic drivers of Arctic sea ice decline since the turn of the century» is held Thursday March 11 at 14:15. The defense and trial lecture will be streamed.

Sea ice appears in large variability of different ice types that have a wide range of characteristics. Knowing their distribution is important for safe ship navigation in icy waters. Foto: Johnannes Lohse.

With the Arctic sea ice continuously decreasing in both extent and thickness, fast and robust production of reliable ice charts becomes more important to ensure the safety of Arctic operations. This thesis focuses on the development of automated algorithms for the mapping of sea ice from synthetic aperture radar (SAR) images. It presents a thorough background on the topics of sea ice observations and ice charting, sea ice image classification, and the appearance of sea ice in SAR imagery. Three papers present the scientific developments in the thesis.

Paper 1 focuses on the topic of feature selection. The study investigates the benefits of splitting a multi-class problem into several binary problems and selecting different feature sets specifically tailored towards these binary problems. Using a combination of classification accuracy and sequential search algorithms, the best order of classification steps and the optimal feature set for each class are found and combined into a numerically optimized decision tree. The method is tested on various examples, including an airborne, multi-frequency SAR data set over sea ice, and compared to traditional classification approaches.

Paper 2 and 3 focus on the classification of Sentinel-1 (S1) wide-swath SAR images. Both papers use a newly generated training and validation data set for different sea ice types, which is is based on the visual analysis of overlapping S1 SAR and optical data. A particular challenge for the automated analysis of wide-swath SAR images is the surface-type dependent variation of backscatter intensity with incident angle (IA). In Paper 2, a novel method to directly incorporate this per-class IA effect into a classification algorithm is developed. Paper 3 investigates the IA dependence of texture features and extends the algorithm from Paper 2 to include textural information, in order to solve the ambiguities inherent in a classifier based on intensity only.

His supervisors are:

  • Associate Professor Anthony Doulgeris, Department of Physics and Technology, UiT (main supervisor)
  • Researcher Wolfgang Dierking, Department of Physics and Technology

Mem bers of the evaluation committee are:

  • Professor John Yackel, Department of Geography, University of Calgary, Canada (1. Opponent)
  • Dr. Natalia Zakhvatkina, Arctic and Antarctic Research Institute (AARI) and Nansen International Environmental and Remote Sensing Centre (NIERSC), Russia (2. Opponent)
  • Dr. Jack Landy, Department of Physics and Technology, UiT (internal member and leader of the committee)

Leader of the public defense:
The leader of the public defense is Professor Camilla Brekke , Vice-Dean Research, Faculty of Science and Technology, UiT.

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