ALMA, a tool to study sound propagation in fluctuating oceans: latest evolutions and analyses

Recent advances and evolutions of the ALMA (Acoustic Laboratory for Marine Applications) project are tackled in this paper. While the system's goal continues to gather experimental data to share with the community and understand the underlying phenomena linked with ocean fluctuations and their interactions with sound waves propagation, the technological and technical updates of the system also allowed to conduct some measurements of the ambient noise properties. Both of these two aspects of the work conducted with ALMA are the topic of this paper: on one hand, the effect of temperature fluctuations on the variation of the estimated direction of arrival of acoustic waves emitted from a fixed source was previously shown and is studied here from a statistical point of view. In fact, the distribution of the normalized acoustic intensity is computed in different configurations and serves as an efficient tool to discriminate between the various regimes of fluctuations involved. On the other hand, noise properties (directivity, coherence) are studied and the design of the 2018 ALMA passive acoustic array is discussed.