Development of an automatic station for acoustic measurements to continuously evaluate the underwater volcanic degassing.

Our project aims at designing and realizing an autonomous hydroacoustic measurement system (“Bubblephone”) allowing to passively monitor the bubbling activity in underwater or lake degassing areas. Hydroacoustic activity is usually measured by the hydrophones of Ocean Bottom Seismometers (OBS) only at low frequencies (1-100 Hz) and in a band disturbed by turbulence, while bubbling emits energetic acoustic activity at higher frequencies (~ 1 kHz) that depend on the size of the bubbles. The station's functions are to filter the hydrophone signals to acquire the high-frequency signals emitted by the bubbles, to calculate and store their frequency spectra and also raw data sequences. The post processing will allow to evaluate the variations of the volume of the bubbles and thus of the degassing in the course of time. The electronics will have an autonomy of 6 months and will be installed in a hyperbaric chamber to be able to go to depths of kilometres.  It will be able to be deployed for several months near active volcanoes and to monitor the degassing of a submarine volcano.