This research project aims at the development and validation of acoustic remote sensing systems and inversion methods for the reliable, rapid environmental assessment (REA) of shallow water areas. One of the most promising REA concepts is to use a field of sonobuoys, deployed either from the air or from surface ship, to receive signals from a controlled sound source or sources of opportunity. The acoustic data, radio telemetered to the aircraft or ship, are processed to determine the range-dependent, water-column and bottom acoustic properties over the area spanned by the drifting buoys. The resulting environmental parameters integrated with concurrent oceanographic measurements are then used to initialize and calibrate oceanographic prediction models for nowcast and forecast environmental hazards in potential areas. The proposed research work directly stems from previous efforts carried at University the Bruxelles and at SACLANT Undersea Research Center for geoacoustic inversion techniques with random fields of sonobouys and at University of Algarve, in the context of experimental testing of ocean acoustic tomography with sources of opportunity. In particular, proved concepts under static conditions, such as the use of a broadband coded signal propagated between a single sound source and a single hydrophone or a fixed array of hydrophones, will be extended to the dynamic configuration of freely drifting sonobuoys.

Objectives:

1. Data-oriented segmentation and inversion algorithms for range-dependent, geoacoustic mapping and seabed characterization;
2. Optimization algorithms for environmental focusing and water-column parameter estimation from the acoustic field received from non-cooperating sources on a random field of sonobuoys;
3. Integration of on-site simultaneously measured oceanographic data as apriori information to constrain the tomographic inversion;
4. Investigation of stochastic approaches to the signal processing and propagation modeling supporting the inversion of broadband acoustic
signals.
5. Study of sensitivity to bottom parameters and robustness against oceanographic and acoustic variability using existing SACLANTCEN datasets collected under diverse conditions;
6. At-sea validation under complex environmental conditions and concluding on the capabilities and limitations of the proposed methods and their applicability under realistic at-sea operations.