Passive pressure and vector geoacoustic inversion offshore Amazon Rio mouth: A sensitivity study

Ship noise is a good resource for passive waveguide characterization in coastal areas due to the high maritime traffic density. Its broadband spectrogram often exhibits environmental determined interference pattern but has weak dependence on source spectral characteristics. The interference pattern has been exploited in an acoustic interferometry technique to characterize the main sediment geoacoustic parameters. To estimate more environmental parameters and examine the benefits of using different acoustic fields, numerical tests using pressure, vertical pressure gradient and vertical waveguide impedance are performed under the environmental model of offshore Amazon Rio mouth (CANOGA 12). The inversion is performed by a global optimization through minimizing a Bartlett-type cost function over a number of discrete frequencies. The synthetic test results demonstrate that the vertical waveguide impedance can give more reliable and higher resolution results compared to that of pressure and vertical pressure gradient, especially for the density of bottom layers. The numerical results comply well the preliminary results obtained from the CANOGA 12 ship noise data, in which, the vertical waveguide impedance also provides closer estimates to the ground truth than that of pressure and pressure gradient. Both synthetic and real data promising results of the vertical waveguide impedance are originated in its intrinsic feature of source spectral level independent, which is preferred in passive acoustics.