Acoustic discrimination between biological objects and gas bubbles in the sea

Alle nødvendige studiepoeng ved universitetet har blitt samlet inn og godkjent (for akademiske klasser, konferanse- oppmøte, formidling osv.). Doktorgradsavhandlingen (synthesis med fire vitenskapelige artikler) har blitt sendt og er akseptert for evaluering av universitetet. To av fire vitenskapelige artikler er nå publisert i en høytstående, fagfellevurderte vitenskapelige journalen (ICES JMS). Tredje artikkelen er ferdig, sendt og for tiden i anmeldelsen på en annen høytstående, fagfellevurderte journalen (JASA). Fjerde artikkelen inngår i doktorgradsavhandlingen som en "manuskript".

Acoustic methods for underwater studies have the necessary potential for monitoring and quantification of natural and man-made gas bubble seeps in the sea. Advanced echo sounders can offer better observation resolution in time and space than any other cur rently available method for gas seep studies. Therefore, echo sounder technology is chosen by Metas to be used for development of new gas seep detecting unit to be manufactured and commercially sold. The proposed PhD project will aim to deliver lacking sc ientific knowledge needed for successful development of this product, while in the same time PhD thesis will be prepared and defended. Gas bubbles, observed by echo sounder, can often look very similar to fish or zooplankton. There are little to none res earch done showing how to acoustically discriminate biological objects and gas bubbles occurring together in the sea. Selected fish species, recognised as representative for the purpose, will be observed using advanced scientific echo sounders, both unde r controlled environment of a fish cage and in the open sea. Small population of caged saithe and mackerel will be investigated with dorsally and ventrally observing echo sounders and horizontally looking stereo camera system for fish orientation and leng th measurements. Similar experimental setting will be used to observe controlled gas bubble releases in large, deep water-filled bag, enabling quantification of both acoustic echo and behaviour properties of gas bubbles. The collected data will be scrutin ized in order to find best available acoustic echo and behaviour based discriminators between biological objects and gas bubbles. The ideas will be further tested using in situ data on gas bubbles and fish/zooplankton occurring together in the water colum n. Most important challenge will be to recognise differing, but stable and quantifiable, acoustic echo and behaviour properties of biological objects and gas bubbles, as observed by echo sounders only.