Sensing of Ice Coverage for Underwater Acoustic Propagation in the Marginal Ice Zone (MIZ)

The experimental work presented in this paper was aimed at studying the influence of the sea ice on acoustic propagation. Recent changes experienced by the Arctic Ocean lead to the belief that the overall knowledge on environmental acoustics in the region has to be updated. In particular, the retreat of the sea ice cover leads to new propagation conditions at the sea surface: thin and fragile young ice. The result is a cracked sea ice landscape. Its influence on underwater sound propagation is the main goal of our study. Our analysis focuses on data collected during the Nordic Recognized Experimental Picture (NREP), conducted by the NATO STO Centre for Maritime Research and Experimentation (CMRE) in June 2023 in the Fram Strait. This paper is dedicated to relating metrics describing the propagation condition (mainly the ice cover) and the observed fluctuations of acoustic paths. Remote sensing tools based on multi-sensor data fusion have been implemented to estimate the spatial distribution and location of ice floes at the sea surface. The resulting range and time dependent transects of the sea ice distribution are compared to the estimated Channel Impulse Response (CIR) obtained by match filtering acoustic waveforms transmitted from the support vessel, NRV Alliance, and received by single-hydrophone sonobuoys. A first-baseline- sonobuoy was deployed in open waters, while a second one was deployed within the ice field. Comparisons between the two CIRs show that the ice cover acts as an attenuator for acoustic intensity. Our study focuses on mid-frequency acoustics (center frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{c}= 1.15$</tex> kHz). The results show a strong dependence in the sea ice cover for multipath propagation: as the sea ice concentration increases (from 7 to 20%, the magnitude of these reflected paths signifcantly diminishes by approximately 5dB).