Analysis of the vertical structure of deep ocean noise using measurements from the SPICEX and PhilSea experiments

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There are open research questions about the vertical structure of low-frequency ambient noise in deep water. For example Gaul et al.'s [IEEE JOE (2007)] analysis of the Church Opal data set showed that noise decreases substantially (on the order of 20 dB) below the critical depth, whereas other researchers have reported more modest reductions [Morris, J. Acoust. Soc. Am. (1978)]. Two deep water experiments provided a unique opportunity to measure ambient noise using large vertical arrays. In 2004–2005, SPICEX used two arrays to sample a North Pacific environment. One array was centered on the sound channel axis, and the other array had hydrophones above and below the critical depth. In 2010–2011, the PhilSea experiment deployed a single array with 150 hydrophones spanning the full water column. Both experiments made repeated short measurements (each 2–3 min long) of the field at the arrays. This talk compares the ambient noise observed during SPICEX and PhilSea with results reported in the literature. Since these data sets contain receptions over the period of a year, we focus on the seasonal dependence of the noise field. In addition to investigating noise level as a function of depth, we consider wind dependence and vertical directionality.