Analysis of spatial reverberation statistics in the central Arctic

Abstract

The horizontal covariance structure of long-range acoustic transmissions measured during the CEAREX 89 experiment is evaluated. Air-gun signatures received at a two-dimensional, horizontal array are processed for signal covariance at bubble pulse frequencies. The modal spectrum of the received signals is compact due to mode stripping, and the signals received on the array have low signal to noise ratio since the source level of the air gun is insufficient to overcome the spreading and scattering losses to the receiving camp. To increase SNR the received waveforms are stacked over 27 shots. The resulting waveforms exhibit the extremely high coherence characteristic of Arctic propagation. The average signal is removed from the stacked waveforms and the spatial covariance of the residual scattered field is estimated at the air-gun bubble pulse frequencies. The resulting statistics show the anisotropy characteristic of low grazing angle rough surface scattering. Based on these observations, an inversion for the spatial statistics of the ice canopy roughness is obtained using an elastic perturbation theory parametrization.