Acoustic Receiving at Long Ranges using Mobile Platforms
Abstract
The overarching goal of this work is to advance the effectiveness of mobile platforms as long-range underwater acoustic receivers. G,lider-type AUVs have been used to receive acoustic transmissions from ~250-Hz broadband sources at ranges of hundreds of kilometers,during deep ocean acoustic tomography experiments in the Canada Basin and the Philippine Sea. In these experiments, the glider-base,d receivers complement data received on fixed acoustic transceiver moorings by providing both direct measurements of ocean temperatu,re and salinity that characterize the sound propagation environment, but also acoustic receptions at many ranges relative to the tra,nsmitting sources. The dataset collected in the Canada Basin is particularly interesting due to the presence of a subsurface local,sound speed minimum at approximately 180 m depth, referred to as the Beaufort Duct, that concentrates the acoustic energy and enable,s sound transmission to long ranges. Acoustic data were collected on the gliders at ranges up to 480 km from transmitting sources., Data will be used to study this ducted acoustic propagation as it evolves with range. In particular we will take a close look at w,hat we refer to as the fold-over feature of the acoustic timefront within the depth span of the duct, where the peak intensity of,the timefront arrives prior to the final cutoff. We are interested in whether this is predictable and how this feature corresponds,with the low-angle modal arrivals. Comparisons with braodband parabolic equation predictions indicate that the peak arrival is more, intense than predicted and at short ranges have revealed extra arrivals that are not present in predictions. Utilizing acoustic ra,ys and broadband parabolic equation and mode models, we will explore the prevalence of these features throughout the dataset as well, as the predictability of these features and their dependence on range.The ultimate goal for the inclusion of these datasets in tomo,graphy experiments is to use the mobile acoustic receivers as additional nodes in the tomography array. We will begin to explore th,is initially using the dataset alone and also combined with the moored data as part of a larger tomographic solution for the Canada,Basin, working with colleagues at the Scripps Institution of Oceanography. Work leading up to this has focused on the localization,of the mobile platforms underwater using these long-range acoustic signals as the uncertainty in vehicle position leads to uncertain,ty in sound speed in a tomographic inversion. The broadband nature of the tomography signals provide travel time resolution that en,abled an order of magnitude improvement in positional uncertainty for these vehicles. We will continue to improve upon progress tha,t was made using data collected in both the Canada Basin and the Philippine Sea experiments by working to automate the matching of m,easured acoustic arrivals with acoustic predictions and to generalize the results to be applicable to other receiving platforms and,acoustic propagation environments.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 10, 2021
- Source ID
- N000142212034
Entities
People
- Lora J. Van Uffelen
Organizations
- Office of Naval Research
- United States Navy
- University of Rhode Island