2023_programme: Latest evolutions of the ALMA system.

• Session: 11. Prospective underwater acoustics : at-sea experiments
  Organiser(s): Jean-Pierre Sessarego, Dominique Fattaccioli and Gaultier Real
• Lecture: Latest evolutions of the ALMA system.
  Paper ID: 2011
  Author(s): Real Gaultier, Fattaccioli Dominique, Beaumont Guillaume, Emmetière Rémi, Le Page Yann
  Presenter: Real Gaultier
  Abstract: ALMA (Acoustic Laboratory for Marine Applications) is a multiple-element acoustic system designed to address future problems in underwater acoustics. It is composed of multiple autonomous sources and a modular passive acoustic array. \nThe latter consisted of 16 basic units of 8 hydrophones, connected to a digitization case and a rigid arm arrangeable in various shapes. A surface buoy was used for synchronization between the cases and data storage. The data were recorded at a fixed rate of 48 kHz.\nA solution developed by ALSEAMAR was applied to redesign the ALMA system : the AGLIMMS (Acoustic GLIder Mission Management System) acquisition system, with synchronization distribution and tunable sampling frequency (up to 96kHz). Unlike the previous version, this acquisition system does not present a limit regarding the number of basic system to serialize. Moreover, it supports the energy storage required by a system composed of a large number of channels, thanks to its low power consumption.\nThe number of hydrophones was increased to 192 channels and a specific design for a planar array was proposed. The hydrophones were disposed following a logarithmic spiral distribution, allowing to reduce the contribution of grating lobes outside of the Shannon-Nyquist spatial sampling criterion. \nAn experiment was performed in the Mediterranean sea, near the shore of Toulon, in March 2022, to qualify the system. The active source were also redesigned in order to increase their coverage in the high frequency range and a tow fish was designed to embark both sources. \nThe presentation will focus on these evolutions and a report of the experiment will be shared.
• Corresponding author: Dr Gaultier Real
  Affiliation: DGA Naval Systems
  Country: France
  e-mail: