Sequential geoacoustic inversion for mobile and compact source–receiver configuration

Abstract

The development of light instrumentation for geoacoustic characterization requires higher-frequency transmissions and inversion methods suitable for mobile configurations that efficiently combine any a priori knowledge about the environment or the time-varying source–receiver geometry and the acoustic transmission measurements. Sequential filtering methods provide a framework to achieve these objectives. In this paper, repeated short-range acoustic transmissions (between 750 and 1500 m) acquired on a drifting 4-hydrophone array that spans a small part of the water column, are sequentially inverted in nonlinear Kalman filters. The sequential filtering approach is demonstrated on actual data from the MREA/BP07 sea trial, with a space-coherent processing of multitone signals and a phase-coherent processing of linearly frequency modulated signals, in low (250–800 Hz) and medium (800–1600 Hz) frequency bands. The sequential inversion of repeated acoustic transmissions shows a good agreement with hydrographic and geophysical data with more stable estimates than conventional metaheuristic inversion results and a reduced computational cost. The effect of filter covariance tuning is also examined and monitored with statistical tests. For large propagation modeling uncertainty, extended Kalman filter and ensemble Kalman filter are of comparable accuracy in parameter tracking, but the ensemble method should be preferred to get reliable associated uncertainty estimates.