WAVENUMBER TRACKING IN A LOW RESOLUTION FREQUENCY-WAVENUMBER REPRESENTATION USING PARTICLE FILTERING

In underwater acoustics, shallow water environments (d < 200 m) act as dispersive waveguide when considering low-frequency sources (f < 250 Hz), and propagation is described by modal theory. Propagated signals are usually multicomponent, and the group delay of each mode (each component) is dispersive and varies with mode number. The waveguide dispersion is characterized by modal wavenumbers, which are widely used as inputs of inversion algorithms to estimate environmental properties. Considering a horizontal array and a source along the axis of the array, wavenumber estimation is equivalent to spectral analysis in the range dimension. A large number of hydrophones (i.e. range samples) is thus required to perform an accurate wavenumber (i.e. spectral) estimation. This paper proposes an original approach for estimating the wavenumbers using a short array and a broadband low-frequency source. The wavenumbers are tracked in the frequency-wavenumber (f - k) domain using particle filtering. The waveguide physics provides generic system and state equations to model the f - k diagram. In particular, it is possible to define an iterative relationship for wavenumber at two consecutive frequencies using the dispersion relation, which holds true in every waveguide. The proposed method provides interesting results on simulated data using 10 hydrophones. It is validated on experimental data recorded in the North Sea.