Please join us for the following AOS Seminar for Thursday, May 11 at 4:00 PM in Spiess Hall Room 330.
Speaker: Dieter Bevans, Scripps Institution of Oceanography
"Head Wave Inversion Technique utilizing the Low-Frequency Sound from a Robinson R44 Helicopter"
A series of underwater acoustic experiments using a Robinson R44 helicopter and an underwater receiver station have been conducted in shallow (16.5 m) water. The receiver station consisted of an 11-element nested hydrophone array with a 12 m aperture configured as a horizontal line (HLA) 0.5 m above the seabed. A microphone was located immediately above the surface. The main rotor blades of the helicopter produce low-frequency harmonics, the fundamental frequency being ~13 Hz. The tail rotor produces a sequence of harmonics six times higher in frequency. The bandwidth of the sound generated by the helicopter is ~10-5000 Hz. An analytical solution has been developed using a 3-layer (atmosphere-ocean-sediment) acoustic propagation model for the horizontal coherence for the head wave. Based on this solution a geoacoustic inversion technique has been developed. The sound speed in the sediment is recovered by comparing the coherence function from the data with the theoretical coherence. The results from the theoretical model and an experiment conducted north of Scripps Pier off the coast of southern California are presented.
[Research supported by ONR, SMART(DOD), NAVAIR, and SIO]
Speaker: Eric Gallimore, Scripps Institution of Oceanography
"Autonomous Target Reacquisition using Scalar Magnetometers"
Work is proposed to perform synthetic processing of magnetometer data in real time aboard an autonomous underwater vehicle (AUV), and use this drive a series of advanced autonomy behaviors. This system will be capable of autonomous identification, localization, and characterization of targets when conducting a seabed survey.