Session 1pUW: Seabed Scattering: Measurements and Mechanisms II 1pUW5. Non-invasive characterization of fluid mud from scalar and vector noise fields due to a small boat

The geoacoustic characterization of sediment using the ratio between passive pressure and vector fields that are measured by a single pressuregradient receiver system is discussed. The ratio is highly sensitive to environmental properties but independent of unknown source spectrogram, e.g., boat noise that exhibits complex time-varying spectral shape. Noise data sets due to different runs with a small boat were recorded on two closely-spaced hydrophones offshore the Amazon Rio mouth in June 2012 and processed by a nonlinear inversion scheme. Global optimization based on genetic algorithms provides 12 parameters describing the run geometry and physical properties of a fluid mud and underlying mud sediment, and the associated marginal posterior probabilities. Good consistency among the inversion results of the different datasets demonstrates the feasibility of the method for environmental characterization under far from ideal conditions, in term of lack of precise navigation data, unknown source spectra, uncertain receiver depth and tilt, etc.