Mechanisms of attenuation of acoustic waves in antarctic ice

Abstract

To guide in the design of an array of acoustic detectors of ultrahigh-energy neutrino interactions leading to electromagnetic cascades in the antarctic ice, estimates of acoustic wave attenuation in the frequency regime 1 to 100 kHz are made. The mechanisms are scattering and reflection at grain boundaries and energy loss due to internal friction. For South Pole ice at −55°C, internal friction is mainly due to proton reorientation and is small enough to permit acoustic waves at all frequencies of interest to propagate through more than 102 m. At frequencies above ∼ 20 kHz the attenuation is mainly due to Rayleigh scattering at grain boundaries. For a mean crystal radius of 0.1 cm at 1 km depth, estimated from available data, it is concluded that, even for a random distribution of c-axes, acoustic waves throughout the frequency regime of interest will lose less than ∼ 1 dB per 100 m at −55°C. Dispersion of arrival time and energy of the acoustic wavefront due to attenuation will not degrade the ability to measure the direction and energy of the cascade.