Disputation: Stig Asle Vaksvik Synnes

Doctoral candidate Stig Asle Vaksvik Synnes at the Department of informatics, Faculty of Mathematics and Natural Sciences, is defending the thesis Advanced Processing for Synthetic Aperture Sonar for the degree of Philosophiae Doctor.

Picture of the candidate

Photo: FFI

The University of Oslo is closed. The PhD defence and trial lecture will therefore be fully digital and streamed directly using Zoom. The host of the session will moderate the technicalities while the chair of the defence will moderate the disputation.

Ex auditorio questions: the chair of the defence will invite the audience to ask ex auditorio questions either written or oral. This can be requested by clicking 'Participants -> Raise hand'. 

Trial lecture

Title: "Target recognition techniques in SAR and SAS"


Main research findings

Synthetic aperture sonar (SAS) is a technique for acoustic imaging and mapping of the seafloor. SAS systems are typically operated from autonomous underwater vehicles in a side-looking configuration. They can provide images with resolution down to a few centimeters out to a range of several hundred meters. The high resolution is obtained through the SAS processing, where measurements recorded at different positions are combined coherently by accounting for the vehicle navigation.

In this work I investigate the information collected by SAS systems that is not expressed directly in the SAS intensity images. This includes information that can be used to refine the navigation solution for the AUV, and information on physical properties that can support the detection and classification of objects of interest. I establish the spatial coherence of speckle for SAS systems, and use this to obtain successful repeat-pass SAS micro-navigation updates with ten times the track separation reported in earlier studies. I establish the support and quality of frequency- and aspect-dependent information for SAS systems, and improve interferometric depth estimates by incorporating the frequency-dependent data quality. I extract information on aspect-dependent scattering from objects on the seafloor, and develop a calibration target for extraction of the frequency dependency.

Adjudication committee:


  • Professor Hugh Griffiths, University College London, UK
  • Research scientist Angeliki Xenaki, NATO Centre for Maritime Research and Experimentation, Italy
  • Professor emeritus Tor Sverre Lande, Department of Informatics, University of Oslo, Norway


  • Professor II Roy Edgar Hansen, Norwegian Defence Research Establishment (FFI) and Department of Informatics, UiO, Norway
  • Professor Andreas Austeng, Department of Informatics, UiO

Chair of defence

  • Professor Ole Hanseth, Department of Informatics, UiO

Contact information to Department: Anniken R. Birkelund

Publisert 3. juni 2021 15:49 - Sist endret 22. nov. 2022 10:10