scholarly journals Predicting the Effects of Random Ocean Dynamic Processes on Underwater Acoustic Sensing and Communication

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Byunggu Cho ◽  
Nicholas C. Makris
Keyword(s):  
Dynamic Processes ◽  
Acoustic Sensing ◽  
Underwater Acoustic ◽  
Ocean Dynamic

scholarly journals The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing in the Ocean

2019 ◽  
Vol 11 (21) ◽  
pp. 2464 ◽  
Author(s):  
Daniel Duane ◽  
Byunggu Cho ◽  
Ankita D. Jain ◽  
Olav Rune Godø ◽  
Nicholas C. Makris
Keyword(s):  
Remote Sensing ◽  
Long Range ◽  
Cross Sections ◽  
Electromagnetic Waves ◽  
Low Frequency ◽  
Wide Area ◽  
Line Transect ◽  
Acoustic Sensing ◽  
Underwater Acoustic ◽  
Primary Means

Acoustics is the primary means of long-range and wide-area sensing in the ocean due to the severe attenuation of electromagnetic waves in seawater. While it is known that densely packed fish groups can attenuate acoustic signals during long-range propagation in an ocean waveguide, previous experimental demonstrations have been restricted to single line transect measurements of either transmission or backscatter and have not directly investigated wide-area sensing and communication issues. Here we experimentally show with wide-area sensing over 360° in the horizontal and ranges spanning many tens of kilometers that a single large fish shoal can significantly occlude acoustic sensing over entire sectors spanning more than 30° with corresponding decreases in detection ranges by roughly an order of magnitude. Such blockages can comprise significant impediments to underwater acoustic remote sensing and surveillance of underwater vehicles, marine life and geophysical phenomena as well as underwater communication. This makes it important to understand the relevant mechanisms and accurately predict attenuation from fish in long-range underwater acoustic sensing and communication. To do so, we apply an analytical theory derived from first principles for acoustic propagation and scattering through inhomogeneities in an ocean waveguide to model propagation through fish shoals. In previous experiments, either the attenuation from fish in the shoal or the scattering cross sections of fish in the shoal were measured but not both, making it impossible to directly confirm a theoretical prediction on attenuation through the shoal. Here, both measurements have been made and they experimentally confirm the waveguide theory presented. We find experimentally and theoretically that attenuation can be significant when the sensing frequency is near the resonance frequency of the shoaling fish. Negligible attenuation was observed in previous low-frequency ocean acoustic waveguide remote sensing (OAWRS) experiments because the sensing frequency was sufficiently far from the swimbladder resonance peak of the shoaling fish or the packing densities of the fish shoals were not sufficiently high. We show that common heuristic approaches that employ free space scattering assumptions for attenuation from fish groups can lead to significant errors for applications involving long-range waveguide propagation and scattering.

Model Analysis of Underwater Acoustic Sensing with Hollow-Core Photonic Bandgap Fiber

2014 ◽  
Vol 568-570 ◽  
pp. 581-589
Author(s):  
Adel Abdallah ◽  
Chao Zhu Zhang ◽  
Zhi Zhong
Keyword(s):  
Acoustic Pressure ◽  
Photonic Bandgap ◽  
Single Mode ◽  
Single Mode Fiber ◽  
Elastic Model ◽  
Hollow Core ◽  
Detection Range ◽  
Acoustic Sensing ◽  
Underwater Acoustic ◽  
Photonic Bandgap Fiber

Recently, using hollow-core photonic bandgap fiber (HC-PBF) for underwater acoustic sensing has been tested experimentally. Besides its unique characteristics and advantages over conventional single mode fiber (SMF), it provides higher responsivity to acoustic pressure. A robust deep water ray tracing model for multipath acoustic signals propagation and the elastic model of HC-PBF are both required to study the effects of underwater enviroment on the propagating acoustic signal for sensing with HC-PBF hydrophones. The combination of the two models allows studying the frequency response, sensitivity, detection range, and maximum operating depth of the HC-PBF hydrophones. The models analysis and simulations show the considerations that must be taken into account for the design and field operation of the HC-PBF hydrophones. In this paper, a complete package to study, design, optimize, and analyze the simulation results of the interferometric HC-PBF hydrophones is proposed.

scholarly journals The Use of Underwater Gliders as Acoustic Sensing Platforms

2019 ◽  
Vol 9 (22) ◽  
pp. 4839
Author(s):  
Cheng Jiang ◽  
JianLong Li ◽  
Wen Xu
Keyword(s):  
Energy Consumption ◽  
Target Detection ◽  
Large Scale ◽  
Transmission Loss ◽  
Low Energy ◽  
Acoustic Sensing ◽  
Underwater Acoustic ◽  
Underwater Gliders ◽  
Sensing Platform ◽  
Low Energy Consumption

Underwater gliders travel through the ocean by buoyancy control, which makes their motion silent and involves low energy consumption. Due to those advantages, numerous studies on underwater acoustics have been carried out using gliders and different acoustic payloads have been developed. This paper aims to illustrate the use of gliders in underwater acoustic observation and target detection through experimental data from two sea trials. Firstly, the self-noise of the glider is analyzed to illustrate its feasibility as an underwater acoustic sensing platform. Then, the ambient noises collected by the glider from different depths are presented. By estimating the transmission loss, the signal receiving ability of the glider is assessed, and a simulation of target detection probability is performed to show the advantages of the glider over other underwater vehicles. Moreover, an adaptive line enhancement is presented to further reduce the influence of self-noise. Meanwhile, two hydrophones are mounted at both ends of the glider to form a simple array with a large aperture and low energy consumption. Thus, the target azimuth estimation is verified using broadband signals, and a simple scheme to distinguish the true angle from the port‒starboard ambiguity is presented. The results indicate that the glider does have advantages in long-term and large-scale underwater passive sensing.

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