is a principal scientist at FFI, while Andreas Austeng is a professor at UiO. I am employed at FFI, where I started in 1998 after receiving my degree of Cand. Scient. in Physics from the University of Bergen. The work on the thesis was conducted as a part of my job over the years 2011 -2021, and was funded by FFI's projects on synthetic aperture sonar (SAS). These SAS projects have been run and financed through a collaboration between FFI, Kongsberg Maritime and the Royal Norwegian Navy. This thesis includes a collection of five papers, placed and presented in a larger common perspective. I first place the title topic of "Advanced SAS" in a greater context. Then I present each of the individual papers, and give an updated review on their topics. I follow up with a discussion on my contributions in a greater perspective, before I summarize my findings and conclude.
In April of 2011, FFI led a sea trial near Larvik, Norway on FFIs research vessel the H.U. Sverdrup II with participation by representatives from Canada, United States, and France. One objective of the sea trial was to acquire a data set suitable for examining incoherent and coherent change detection and automated target recognition (ATR) algorithms applied to Synthetic Aperture Sonar (SAS) imagery. The end goal is to produce an automated tool for detecting recently placed objects on the seafloor. To test these algorithms two areas were chosen, one with a comparatively benign seafloor and one with a boulder strewn complex seafloor. Each area was surveyed before and after deployment of objects. The survey time intervals varied from two days to eight days. In this paper we present the trial and show examples of SAS images and change detection of the images.
This paper presents signal processing techniques particularly suited for interferometric Synthetic Aperture Sonar (SAS) systems onboard Autonomous Underwater Vehicles (AUV) (or other platforms carrying high grade navigation systems). The signal processing is applied to data collected in a controlled rail experiment at Elba Island, Italy, using a wideband interferometric SAS and an Inertial Navigation System (INS). We evaluate different strategies in fusing sonar micronavigation by the Displaced Phase Center Antenna (DPCA) technique with Aided INS (AINS). We obtain highest navigation accuracy using DPCA as aiding sensor into the AINS, then using raw DPCA surge and sway in combination with the AINS attitude and position. Coarse cross correlation based bathymetry and full resolution interferometry (based on the interferogram) is tested on the full swath and objects. Coarse bathymetry is more reliable than the interferogram technique. Phase wraparounds are avoided by estimating the coarse bathymetry first, then using the full resolution phase estimates as correction. Although much work remains, this technique does show a clear potential in improving object classification ability.
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