A wideband moving coil electrodynamic transducer system for autonomous underwater vehicle-based geoacoustic inversion

Abstract

A small expendable wideband low-frequency sound source that will be deployed on the seafloor is being developed to be used for geoacoustic inversion surveys in conjunction with a terrain-hugging AUV. This low-cost deployable source contains a transducer that produces a relatively flat transmit response over the broad frequency band of 100 to 4000 Hz. In operation, a seafloor interface wave will be excited and exploited for geoacoustic inversion by the deployed sound source and a receiving array on the bottom-hugging AUV. A feasibility study is also being performed that includes physics-based sonar simulations to infer the performance of geoacoustic inversion in a number of AUV scenarios and environmental conditions. Based on this study, design trade-offs will be determined to finalize key factors of the transducer, such as its physical size, weight, and production cost. Battery technology is also being developed to optimize the source level, the duty cycle, and the operating life of the signals that will be transmitted during data collection. This effort is being supported by ONR.

Broadband synthetic aperture geoacoustic inversion

“…On the other hand, with relative motion, a waveguide Doppler field computation at x r traces back to multiple source frequencies, see Eqs. (9) and (15). This backward mode-dependent frequency mapping is the main difference when compared to the static field computation.…”

“…(13); (3) Extract the source spectrum S½x r À k n ðv s À v r Þ and compute wðr; z; x r Þ using Eq. (15).…”

“…(15)]. When uniform Doppler is assumed, the source spectrum gets decoupled from the Green's function since Doppler is mode independent.…”

“…However, single-receiver/synthetic aperture inversion methods are preferable operationally due to ease of deployment. 1-14 Furthermore, low SNR methods are attractive due to their ability to use low powered sources, e.g., battery powered acoustic sources, 15 resulting in less disturbance to marine mammals. 4 This paper focuses on matched field inversion for mobile, single source-receiver configurations in low SNR conditions.…”

Recursive Bayesian synthetic aperture geoacoustic inversion in the presence of motion dynamics

“…Alternatively, a battery powered acoustic source may be dropped onto the ocean bottom to aid AUV-based geoacoustic inversion. 20 AUV-based inversions recently have been gaining research interest due to their operational attractiveness. [21][22][23][24] The theory of waveguide Doppler and modal propagation is reviewed briefly in Sec.…”