Oceanic Ambient Noise as a Background to Acoustic Neutrino Detection

TL;DR

This study analyzes deep ocean ambient noise to improve the understanding of background signals for acoustic detection of ultra-high energy cosmic ray neutrinos, revealing stable spectral characteristics and a depth-dependent noise model.

Contribution

It introduces a depth-dependent noise model that accurately fits high-frequency ocean ambient noise data, aiding in neutrino detection efforts.

Findings

Noise spectral shape is stable over months.

Spectral slopes above 15 kHz are steeper than -6 dB/octave.

A depth-dependent model fits the data well up to 25 kHz.

Abstract

Ambient noise measured in the deep ocean is studied in the context of a search for signals from ultra-high energy cosmic ray neutrinos. The spectral shape of the noise at the relevant high frequencies is found to be very stable for an extensive data set collected over several months from 49 hydrophones mounted near the bottom of the ocean at ~1600 m depth. The slopes of the ambient noise spectra above 15 kHz are found to roll-off faster than the -6 dB/octave seen in Knudsen spectra. A model attributing the source to an uniform distribution of surface noise that includes frequency-dependent absorption at large depth is found to fit the data well up to 25 kHz. This depth dependent model should therefore be used in analysis methods of acoustic neutrino pulse detection that require the expected noise spectra.