Geoacoustic Inversion Using an Autonomous Underwater Vehicle in Conjunction With Distributed Sensors

A midfrequency (2-6 kHz) geoacoustic parameter inversion approach is proposed using a moving source and single receiver. The source motion creates a synthetic horizontal line array (SHLA), and the received signals, by source-receiver reciprocity, can be used to estimate the sediment/bottom parameters using matched field inversion (MFI). Using a wideband signal, the arrival times of multipaths are estimated using compressive sensing, from which one can estimate the source-receiver range, water depth, sediment thickness, and sound speed. This information is difficult to get at low frequencies due to the limited bandwidth. MFI is carried out using the frequency-coherent cost function and does not require the data to be precisely synchronized. Sensitivities of inversion of geoacoustic parameters are also studied. Performance using the SHLA is shown to be comparable to that using the conventional horizontal and vertical line array, and is shown to be sensitive to sediment attenuation-one of the difficult parameters to estimate. The proposed scheme uses short range (50-150 m) data, and requires a low-level source that can be carried by an autonomous underwater vehicle (AUV). With the AUV traveling between nodes in a distributed sensors network, the inversion can be conducted over a large area.