2025_programme: Modal inversion of tomographic signals in the Canada Basin

• Day: June 16, Monday
    Location / Time: B. ERATO at 11:40-12:00
• Last minutes changes: -
• Session: 07. Inverse Problems in Acoustical Oceanography
  Organiser(s): Julien Bonnel, Stan Dosso
  Chairperson(s): Julien Bonnel, Stan Dosso
• Lecture: Modal inversion of tomographic signals in the Canada Basin [Invited]
  Paper ID: 2207
  Author(s): F. Hunter Akins, Matthew Dzieciuch, Peter Worcester, Hanne Sagen, Bruce Cornuelle
  Presenter: Hunter Akins
  Abstract: Estimating acoustic medium properties from modal observables such as the horizontal wavenumber or group slowness is a classical inverse problem. This paper presents deep water sound speed inversion of modal group delay measurements from 35-Hz broadband tomographic signals transmitted across the Canada Basin during the Coordinated Arctic Acoustic Thermometry Experiment (CAATEX). The signal is measured on two 1200-m long vertical arrays roughly collocated along a geodesic path at ranges of ~350 km and ~850 km respectively. The received signals are mode filtered, and the modal group delay is estimated for each filtered mode. For particularly dispersive modes, delay estimation is challenging due to distortion in the received waveform. By matching the received modal time series with a replica that models deterministic dispersion, we obtain improved delay estimates. Using the known source-receiver ranges, the forward problem maps the range-averaged sound speed profile along the propagation path to the modal group delays. This forward model is mildly non-linear, and the inverse problem is solved iteratively for each transmission using a linearized forward model from perturbation theory. The solutions provide a sound speed profile estimate for each acoustic transmission, which were made every third day during the deployment from September 2019 to October 2020. These estimates are compared with oceanographic measurements made on the moorings, consisting of temperature measurements at each hydrophone depth as well as a small number of temperature and salinity measurements spaced throughout the mooring. While generally consistent with the mooring measurements, the tomographic profile estimates vary more smoothly from transmission to transmission as they average out smaller scale ocean variability present along the transmission path.
• Corresponding author: Dr F. Hunter Akins
  Affiliation: UC San Diego
  Country: United States