2023_programme: Source parameter estimation : experimental comparison between LFM and MLS waveforms.

• Session: 11. Prospective underwater acoustics : at-sea experiments
  Organiser(s): Jean-Pierre Sessarego, Dominique Fattaccioli and Gaultier Real
• Lecture: Source parameter estimation : experimental comparison between LFM and MLS waveforms.
  Paper ID: 1952
  Author(s): Real Gaultier, Gemba Kay, Lamy Kathrine, Kacel Thomas
  Presenter: Real Gaultier
  Abstract: For underwater source localization, accurate estimation of the time of flight (or travel time) is required and, in the case of a moving platform or a moving source, the observed waveform may include Doppler (waveform dilation). The source waveform thus needs to be sensitive to estimate both time of flight and Doppler. In this study, we compare two waveforms : Linear Frequency Modulated sweeps (LFMs) and Maximum Length Sequences (MLSs). MLSs are based on Pseudo Random Noise (PRN) signals. \nThe performance of time of flight and relative speed estimation between the two waveforms was compared using data gathered during an at-sea experiment conducted in March 2022 near in the Mediterranean Sea, near the coast of Toulon. The trial consisted transmitting the two waveforms using a mobile source. The two waveforms presented identical center frequency (6 kHz) and bandwidth (2kHz). \nOn the receiving end, the signals were recorded by a 192-hydrophone moored bilboard array. The hydrophones were arranged in a logarithmic-spiral form to limit the influence of grating lobes in a wide frequency band. The source-array distance ranged from 2.5 to 8 km, and the source was towed at a constant speed (~1.5m/s) and depth (~50m). The sound speed profile was upward refracting, typical of winter Mediterranean environtments. On the other hand, the bathymetry was strongly range-dependent. \nThe analysis of the recorded signals shows that the MLS waveform outperforms the LFM waveform for estimating time of flight (uncertainty reduced by a factor 4) and radial velocity (uncertainty reduced by a factor 20). \nFirst results focus on single hydrophone processing, but possible applications to 2D array processing are discussed for accurately localizing the source in range-dependent environments.
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• Corresponding author: Dr Gaultier Real
  Affiliation: DGA Naval Systems
  Country: France
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