f Experimental study of temperature effects on air gun signatures

Marine seismic sources have been studied extensively during the last two decades. Both experimental and theoretical studies of air guns and water guns have been performed. One of the main theoretical issues have been to onderstand the damping mechanisme for the bubble oscillations in an air gun pressure signature . Both Ziolkowski (1990) and Laws et al . (1990) pointed out that condensation and evaporation of water vapour across the bubble wall are essential procesnes involved in the damping mechanism. Since these processen are driven by pressure and temperature gradients across the bubble wall, we decided to investigate the influence of changing the temperature of the water surrounding an air gun . From measurements it is well known that the bubble time period changes when the sea temperature changes . However, this knowledge is of qualitative nature, and how other signature characteristics like primary to bubble ratio is influenced by a change in the water temperature is not so well known. In order to quantify these effects, we performed a controlled tank experiment . We used a water tank of approximately 850 litres . In order to attenuate reflections From the walls and the bottom of the tank, absorbers of 5cm thickness were placed inside the tank . The source was a BOLT 6 00 B air gun with a chamber volume of 1.9 cu.in. In all the experiments the firing pressure was 100 bar . The gun was placed at 0.5 m depth, and the hydrophone was placed 0 .22 m from the gun ports.