Trial lecture
“Applications of fixed and data-adaptive rank shaping and regularization of linear inverse problems in ocean acoustics”
Time and place: January 15, 2026 11:15 AM. Kristen Nygaards sal (5370), Ole-Johan Dahls hus.
Main research findings
Modern ultrasound and sonar systems use arrays of sensors that work together to create images from sound waves. The way these sensors are controlled by mathematical "window functions" fundamentally determines imaging performance. This thesis aims to illuminate and expand the role of spatial window functions in array processing within the context of medical ultrasound imaging, demonstrating their significance throughout the imaging pipeline, from transmitting sound waves to evaluating the final image.
The work addresses five core questions related to window functions: how to design transmit sequences that enable accurate recovery of multistatic channel data; how to optimally factor a desired window function into transmit and receive components; how to bound worst-case sidelobe levels under sensor calibration tolerances; how the performance of a nonlinear beamformer can be understood through window functions; and how adaptive windowing can both degrade and improve the estimation of image quality metrics.
Together, these results shed light on the limits and possibilities of window-based array processing, offering practical tools for developing and evaluating beamforming methods.
Adjudication committee
- Professor John Buck, University of Massachusetts, USA
- Professor Alfred Hanssen, UiT The Arctic University of Norway, Tromsø, Norway
- Associate Professor Kristian Gjertsen Kjelgård, Department of Informatics, University of Oslo, Norway
Supervisors
Professor Sven Peter Näsholm, University of Oslo, Norway
Professor Andreas Austeng, University of Oslo, Norway
Chair of defence
- Professor Dag Trygve Eckhoff Wisland, Department of Informatics, University of Oslo
Contact information at Department: Mozhdeh Sheibani Harat