ASPECT-DEPENDENT SCATTERING IN WIDEBEAM SYNTHETIC APERTURE SONAR Stig Asle Vaksvik Synnes a,b , Roy Edgar Hansen a,b a Norwegian Defence Research Establishment (FFI), PO Box 25, NO-2027 Kjeller, Norway. b University of Oslo (UiO), Department of Informatics PO Box 1080, Blindern, N-0316 Oslo, Norway. Contact author: Stig Asle Vaksvik Synnes, Norwegian Defence Research Establishment (FFI), PO Box 25, NO-2027 Kjeller, Norway. E-mail: Stig-Asle.Synnes@ffi.no Abstract: Widebeam synthetic aperture sonar (SAS) gathers information on the acoustic scat- tering over a scene. From the aspect-dependent scattering of facets we can extract information on their orientation and size. This is information that can be useful in target detection and classification. Each pixel of a SAS amplitude image represents the backscattering at a given location. In SAS imaging the backscattering is normally assumed to be independent of look angle within the beamwidth. This assumption of aspect-independent scattering is only valid for narrowbeam systems. For widebeam systems the backscattering of real scatterers can show a strong angu- lar dependency over the beamwidth. We suggest to extract this additional information, and investigate the aspect-dependency of the backscattering going into each pixel. We are able to estimate both the orientation of facets and their size. We demonstrate the method on SAS data recorded from a HUGIN autonomous underwater vehicle using a HISAS system with a proto- type low frequency transmitter covering the band 12-38 kHz with a -3dB beamwidth exceeding 100 degrees at the center frequency. The approach is based on adaptive matched filter feature extraction developed in synthetic aperture radar (SAR). Keywords: Synthetic aperture sonar, matched filter imaging, target response. UACE2015 - 3rd Underwater Acoustics Conference and Exhibition - 129 -