Presentation title: “AUV based geoacoustic inversion”
Presenter: Prof. T.C. Yang
Time: 14:30-16:00 pm, Aug. 2, 2018
Location: Conference Room 315 of the Underwater Acoustic Engineering Building
Short Bio of the presenter:
T. C. Yang received the Ph.D. degree in high energy physics from the University of Rochester, Rochester, NY, USA, in 1971. He is currently a Professor and previously a Pao Yu-Kong Chair Professor at the Zhejiang University. From 2012 to 2014, he was a National Science Counsel Chair Professor at the Nat. Sun Yat-Sen Univ. Kaohsiung, Taiwan. Before that, he spent 32 years working at the Naval Research Laboratory, Washington, DC, serving as Head of the Arctic Section, Dispersive Wave Guide Effects Group, and acting Head of the Acoustic Signal Processing Branch, and consultant to the division on research proposals. His current research focuses on: (1) environmental impacts on underwater acoustic communications and networking, exploiting the channel physics to characterize and improve performance, (2) environmental acoustic sensing and signal processing using distributed networked sensors, and (3) methods for improved channel tracking and data-based source localization. In earlier years, he pioneered matched mode processing for a vertical line array, and matched-beam processing for a horizontal line array. Other areas of research included geoacoustic inversions, waveguide invariants, effects of internal waves on sound propagation in shallow water, Arctic acoustics, etc. He is a fellow of the Acoustical Society of America.
Abstract of the presentation:
Geoacoustic properties of the ocean bottom, such as sediment thickness, sound speed, density, attenuation coefficients are critical for transmission calculations and predictions but they are often very difficult to get since direct measurements based on bottom cores are only good for depth up to 1-2 meters. Matched field inversion (MFI) has been proposed to estimate the geoacoustic properties of the bottom based on low frequency (<500 hz) data received on a vertical line array or a horizontal line array. This method has been extensively studied over the last 20 or so years and demonstrated with experimental data, but its prospect for practical applications is rather limited.
A mid-frequency (2-6 kHz) geoacoustic parameters 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 MFI. Using a wide band signal, the arrival times of multi-paths are estimated using compressive sensing (CS), 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 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 which can be carried by an autonomous underwater vehicle (AUV). With the AUV traveling between nodes in a distributed sensors network (DSN), the inversion can be conducted over a large area.
