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pp. 143-150, vol. 17, 2014
Institute of Oceanology Polish Academy of Sciences, Sopot, Poland
Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland
Key words: sediment; methane; echo parametrisation
Abstract: Gaseous shallow sediment has been recognized in several areas of the Southern Baltic Sea. The most commonly observed manifestation of the gas in the bottom top layer is an acoustic blanking or shadowing resulting from significant attenuation and scattering of acoustic signals in the regions of gas bubble occurrence at the bottom. The main goal of this publication was to examine whether known methods of acoustic echo parameterization generally used to determine the fraction of the surface deposits would be sufficient in determining the extent of the occurrence of gas saturated sediments and areas with periodic gaseous outflows. To this end, a set of an acoustic echo signals recorded in gas seepage regions by using four different frequencies (12, 70, 120 and 200 kHz) was analyzed. To determine the acoustic features of gaseous sediments, based on the shape of the echo envelope, a few statistical parameters, as well as the parameters resulting from a wavelet transform, were calculated. A comparison of the results allowed for a relatively accurate separation of pockmark areas.
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