2025_programme: Acoustic observables and inversions in long-range polar transmissions

• Day: June 16, Monday
    Location / Time: B. ERATO at 17:00-17:20
• Last minutes changes: -
• Session: 07. Inverse Problems in Acoustical Oceanography
  Organiser(s): Julien Bonnel, Stan Dosso
  Chairperson(s): Julien Bonnel, Stan Dosso
• Lecture: Acoustic observables and inversions in long-range polar transmissions [Invited]
  Paper ID: 2235
  Author(s): Emmanuel Skarsoulis, George Piperakis
  Presenter: Emmanuel Skarsoulis
  Abstract: This presentation focuses on the behavior of low-order modes and the definition of meaningful observables in long-range, low-frequency polar transmissions used in ocean acoustic thermometry. The existence of the polar duct, a layer of rapidly decreasing sound speed towards the surface in the upper 300-400 m, gives rise to excessive dispersion which makes it difficult to define observables in the time domain. Even though an increase in transmission bandwidth typically improves the resolvability in the time domain through the decrease in time duration of the emitted pulse, this approach does not work here because of dispersion, and a decrease rather than increase of the bandwidth combined with mode filtering leads to better results. The perturbation behavior of narrow-band mode-filtered arrivals is considered and compared to the predicted behavior based on the notion of travel-time sensitivity kernels (TSKs) revealing a stable and close-to-linear behavior. Then the performance of linear and non-linear (matched-peak) inversion schemes is addressed with the help of synthetic data. The effect of the reference state used for linear inversions and that of the range dependence is studied. Range dependence appears to play a significant role and has to be taken into account for the correct interpretation of modal travel-time data. In addition, the resolving power of single modes and combinations of modes for the retrieval of particular depth layers will be presented. \n\nAcknowledgement: Work funded by the European Union Horizon Europe Programme, Grant Agreement No. 101094621. Views and opinions expressed, however, are those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Executive Agency. Neither the European Union nor the granting authority can be held responsible for them.
• Corresponding author: Dr Emmanuel Skarsoulis
  Affiliation: Institute of Applied and Computational Mathematics - FORTH
  Country: Greece