The detection of acoustic signals from ultra-high energy neutrino interactions is a promising method to measure the flux of cosmogenic neutrinos expected on Earth .
The energy threshold for this process depends strongly on the absolute noise level in the target material .
The South Pole Acoustic Test Setup ( SPATS ) , deployed in the upper part of four boreholes of the IceCube Neutrino Observatory , has monitored the noise in Antarctic ice at the geographic South Pole for more than two years down to 500 \textrm { m } depth .
The noise is very stable and Gaussian distributed .
Lacking an in-situ calibration up to now , laboratory measurements have been used to estimate the absolute noise level in the 10 to 50 \textrm { kHz } frequency range to be smaller than 20 \textrm { mPa } .
Using a threshold trigger , sensors of the South Pole Acoustic Test Setup registered acoustic events in the IceCube detector volume and its vicinity .
Acoustic signals from refreezing IceCube holes and from anthropogenic sources have been used to test the localization of acoustic events .
An upper limit on the neutrino flux at energies E _ { \nu } > 10 ^ { 11 } \textrm { GeV } is derived from acoustic data taken over eight months .