Comparison and combination of modal-dispersion and matched-field inversion for seabed geoacoustic profiles at the New England Mud Patch

This paper considers the information content for seabed geoacoustic inversion of recorded acoustic waveforms processed as modal-dispersion (MD) data (mode arrival times as a function of frequency) and as matched-field (MF) data (multi-frequency complex acoustic fields across a sensor array). These approaches are applied separately and combined in joint inversion, with the MD and MF datasets derived from the same acoustic recordings collected on the New England Mud Patch. At-sea measurements are simpler for MD data, which can be extracted from recordings at a single uncalibrated sensor while MF data require a synchronized, calibrated multi-sensor array. Further, MF inversion requires estimating the source/receiver depths and complex source spectrum. However, MF inversion is sensitive to seabed attenuation and is more easily extended to higher frequencies where mode filtering for MD data is challenging. Comparison of geoacoustic information content is facilitated here using trans-dimensional Bayesian inversion to sample probabilistically over the number of layers of the seabed model as well as over the order of an autoregressive error model. Results indicate MF inversion resolves more-detailed geoacoustic structure with smaller uncertainties, including good estimates of the attenuation profile for wide-band (20–1500 Hz) inversions. No significant advantage is apparent for joint MF/MD inversion.