Ocean ambient low frequency acoustic noise structure in shallow and deep water regions

Abstract
Physical analysis of processes responsible for left hand side spectrum part of ocean ambient low frequency (LF) pressure field formation in ocean is fulfilled, estimate of natural background ULF pressure spectrum levels observed by bottom installed transducer in frequency band 0.03-10.0 Hz are obtained. This interval is laying in fact on the boundary between ultra low (ULF) and low frequency (LF) ocean pressure fields. To derive such estimate two types of results are used - results of direct pressure measurements in the frequency range (30-10000) mHz obtained by authors in sea coastal regions of former USSR (the Black sea, the Japanese sea, the Barentz sea) during multiyear observation cycles, results of pressure measurements fulfilled by other authors, as well as materials of indirect long period gravity waves parameters measurements fulfilled on the sea surface. The latter results were obtained by oceanologists in the form of surface wave oscillations spectra and were transformed by authors in bottom pressure variations by recalculation. On the basis of pressure measurement statistical treatment important conclusion is obtained, that pressure fields observed on ocean bottom in frequency range below 1000 mHz are formed presumably by pressure pulsations produced by long period and wind ocean gravity waves.