An analysis of the temporal fluctuations of cw acoustic propagation in the marginal ice zone

Abstract

Continuous wave (cw) acoustic transmission data from MIZEX 84 (marginal ice zone experiments) were transmitted between two ships separated by approximately 100 km and propagated via a partially ice-covered path. The signals were stepped in frequency between 25 and 200 Hz for 1 h. Both vessels were drifting freely which resulted in a Doppler shift in the received multipath signal. The measured Doppler compares favorably with available navigational data. The quadrature demodulated received signal is modeled as a (locally) wide-sense stationary process. Accordingly, we can exploit the Gaussian correlation structure and estimate the moments of the power spectrum using the covariance method. This method is computationally efficient and relatively unexploited for this purpose. We relate the rms spectral width directly to the variance of the phase rate (ν2). The value of ν2 is a function of oceanic processes which dynamically perturb the sound field. Estimates of ν2 from the MIZEX data are compared with similar experiments carried out in the more quiescent Central Arctic, and in midlatitude regions.