scholarly journals A Study on the Estimation of Source Bearing in an ASA Wedge: Diminishing the Estimation Error Caused by Horizontal Refraction

2021 ◽  
Vol 9 (12) ◽  
pp. 1449
Author(s):  
Jianbo Zhou ◽  
Jun Tang ◽  
Yixin Yang
Keyword(s):  
Acoustical Society ◽  
Estimation Error ◽  
Normal Modes ◽  
Direct Path ◽  
Bearing Estimation ◽  
3D Effects ◽  
Horizontal Refraction

The performance of warping transformation in diminishing the error in underwater source-bearing estimation, caused by horizontal refraction effects (also named 3D effects), is studied. First, the capability of warping transformation for separating the normal modes, as well as their direct and horizontally refracted paths, in a standard Acoustical Society of America (ASA) wedge is demonstrated. Second, the error values for source bearing estimation in three different manners, i.e., using the full signal, using its component corresponding to the first mode, and using the component of the latter corresponding only to the direct path are compared for the same wedge case. The results show that the estimation error can be significantly reduced by beamforming, with only the first mode, or using the direct path of the first mode in cases where there exists a horizontally refracted path of the first mode.

A 2-D DESCRIPTION OF SOUND PROPAGATION IN A HORIZONTALLY-INHOMOGENEOUS OCEAN

2002 ◽  
Vol 10 (01) ◽  
pp. 123-151 ◽  
Author(s):  
OLEG A. GODIN
Keyword(s):  
Travel Time ◽  
Sound Propagation ◽  
Environmental Gradients ◽  
Normal Modes ◽  
Approximate Expression ◽  
Underwater Sound ◽  
Mode Amplitude ◽  
Geometrical Acoustics ◽  
Horizontal Refraction ◽  
Horizontally Inhomogeneous

Effects of horizontal refraction on underwater sound propagation in deep and shallow water are considered within geometrical acoustics and adiabatic normal modes approximations. Several distinct formulations of the adiabatic approximation have been proposed in the literature on modal propagation. These formulations differ in the predicted values of mode amplitudes and, hence, in their reciprocity and energy-conserving properties. The formulations are compared with respect to their accuracy and domain of validity, assuming small and smooth variation of mode propagation constants characteristic of underwater acoustic waveguides. Perturbation theory for horizontal (modal) rays is used in the analysis. An approximate expression for the adiabatic mode amplitude in 3-D problems is derived which requires environmental information only along the source-receiver radial and which has greater accuracy than previous formulations. It is shown that the uncoupled azimuth approximation, also known as the N × 2-D approximation, overestimates travel times of ray arrivals as well as phases of adiabatic normal modes in a horizontally-inhomogeneous ocean. The travel time and phase biases rapidly increase with the value of cross-range environmental gradients and propagation range. Simple and explicit expressions for leading-order corrections to the travel time and the phase are found in terms of path-averaged cross-range environmental gradients. Implications on applicability of the uncoupled azimuth approximation for sound propagation modeling in a horizontally-inhomogeneous ocean are discussed. A perfect-wedge model of the coastal ocean is chosen to illustrate the importance of the travel-time and phase biases due to horizontal refraction.

scholarly journals Transverse horizontal spatial coherence in shallow water

2019 ◽  
Vol 283 ◽  
pp. 02001
Author(s):  
Bo Zhang ◽  
Fenghua Li ◽  
Zhenglin Li ◽  
Yanjun Zhang ◽  
Jingyan Wang
Keyword(s):  
Shallow Water ◽  
Acoustical Society ◽  
Coherence Length ◽  
Environmental Variability ◽  
Northern South China Sea ◽  
Spatial Coherence ◽  
Normal Modes ◽  
Sound Field ◽  
Acoustic Frequency ◽  
Field Correlation

Since the advent of large-aperture array processing, more and more attention has been paid to the sound field correlation, which has fundamental limit to the array gain of spatial coherent signal processing. The two dominant mechanisms that degrade the spatial coherence are normal modes (or multi-paths) interference and the environmental variability caused by several relevant oceanographic processes. In the present study, the transverse horizontal spatial coherence of explosive signals has been studied experimentally by a bottom-mounted array in the Northern South China Sea. And the effects of normal mode interference on the transverse horizontal spatial coherence have been analyzed numerically. Expressed in terms of wavelengths, the coherence length is shown to be larger than 170λ/185λ at acoustic frequency 508-640Hz/80-101Hz in shallow water. It is much greater than Carey’s shallow-water result 30λ estimated from array signal gain after assuming a specific functional form for the coherence (The Journal of the Acoustical Society of America 104, 831 (1998)). It, however, is consistent with Rouseff’s modelling result of a coherence length larger than 100λ (The Journal of the Acoustical Society of America 138, 2256 (2015)). Both Carey and Rouseff argue that the transverse horizontal spatial coherence length depends only weakly on range, in direct. In the present study, however, the coherence length is shown to depend highly on source-receiver range, and it fluctuates synchronously with the sound-field intensity while range varies.

Computing Acoustic Transmission Loss Using 3D Gaussian Ray Bundles in Geodetic Coordinates

2016 ◽  
Vol 24 (01) ◽  
pp. 1650007 ◽  
Author(s):  
Sean M. Reilly ◽  
Gopu R. Potty ◽  
Michael Goodrich
Keyword(s):  
Transmission Loss ◽  
Three Dimensional ◽  
Environmental Parameters ◽  
Test Results ◽  
Geodetic Coordinates ◽  
Large Numbers ◽  
Execution Speed ◽  
3D Effects ◽  
Ray Path ◽  
Horizontal Refraction

This paper defines a new three-dimensional (3D) Gaussian ray bundling model in geodetic coordinates: latitude, longitude, and altitude. Derivations are provided for 3D refraction, 3D interface reflection, 3D eigenray detection, and a 3D variant of the Comprehensive Acoustic System Simulation (CASS)/Gaussian Ray Bundling (GRAB) model. This approach allows environmental parameters and their derivatives are computed directly in latitude, longitude, and depth directions without reducing the problem to a series of [Formula: see text] Cartesian projections. Our model supports 3D effects such as great circle routes and horizontal refraction in sloped environments. Key test results are included for ray path refraction accuracy using a Munk profile, Gaussian beam projection into the shadow zone for an [Formula: see text] linear profile, and horizontal refraction from a 3D analytic wedge. Testing to date indicates that this approach has accuracy at least as good as CASS/GRAB, but with improved execution speed benefits for large numbers of targets, and 3D transmission loss effects.

scholarly journals Three-Dimensional Sound Propagation in the South China Sea with the Presence of Seamount

2021 ◽  
Vol 9 (10) ◽  
pp. 1078
Author(s):  
Shenghao Li ◽  
Zhenglin Li ◽  
Wen Li ◽  
Yanxin Yu
Keyword(s):  
South China Sea ◽  
South China ◽  
Sound Propagation ◽  
Three Dimensional ◽  
Sound Field ◽  
The South China Sea ◽  
China Sea ◽  
3D Effects ◽  
Horizontal Refraction ◽  
2D And 3D

Seamounts have important effects on sound propagation in deep water. A sound propagation experiment was conducted in the South China Sea in 2016. The three-dimensional (3D) effects of a seamount on sound propagation are observed in different propagation tracks. Ray methods (BELLHOP N×2D and 3D models) are used to analyze and explain the phenomena. The results show that 3D effects have obvious impacts on a sound field within a horizontal refraction zone behind the seamount because some sound beams cannot reach the receiver for the horizontal refraction effects, which impacts the sound field within a certain angle range behind the seamount. The arrival structure results show that the eigenrays after horizontal reflection will arrive at the receiver earlier than those obtained from the two-dimensional (2D) model within the horizontal refraction zone behind the seamount. This means that the horizontal reflection effect of a seamount will cause the shortening of sound propagation paths. Finally, in the reflection zone in front of the seamount, the 2D and 3D TL results show that the shape of the reflection zone is similar to an “arch” type, and the horizontal refraction of sound waves has little effect on the TLs in the reflection zone of a seamount.

Active Control of Low Frequency Linear Spectrum by Estimating Receivers Location

2013 ◽  
Vol 816-817 ◽  
pp. 385-388
Author(s):  
Cheng Jun Hu ◽  
Yuan Zheng
Keyword(s):  
Noise Reduction ◽  
Estimation Error ◽  
Low Frequency ◽  
Distance Estimation ◽  
Considerable Effect ◽  
Location Estimation ◽  
Estimation Errors ◽  
Linear Spectrum ◽  
Bearing Estimation ◽  
Reduction Region

An approach to actively control the low frequency linear spectrum in vessel navigation noise is proposed. The approach relies on the introduction of a secondary noise-cancellation source which is fixed aboard and whose signal generation uses the estimated location knowledge of the receiver. Loss of underwater acoustic transmission is modeled and Monte Carlo simulations are conducted to analyze the noise-reduction effects under different location estimation errors. Simulation results show that bearing estimation error is the predominant factor affecting the radius of the effective noise-reduction region, while distance estimation error has considerable effect only when the perpendicular distance from the receiver to vessels course is quite small. Besides, when bearing estimation error is less than 1.2° and distance estimation error is less than 80%, satisfactory noise reduction region can be obtained using the approach.

Temporal Prediction Errors Affect Short-Term Memory Scanning Response Time

2016 ◽  
Vol 63 (6) ◽  
pp. 333-342
Author(s):  
Roberto Limongi ◽  
Angélica M. Silva
Keyword(s):  
Response Time ◽  
Short Term Memory ◽  
Estimation Error ◽  
Predictive Coding ◽  
Time Estimation ◽  
Prediction Errors ◽  
Memory Scanning ◽  
Short Term ◽  
Term Memory ◽  
Temporal Prediction

Abstract. The Sternberg short-term memory scanning task has been used to unveil cognitive operations involved in time perception. Participants produce time intervals during the task, and the researcher explores how task performance affects interval production – where time estimation error is the dependent variable of interest. The perspective of predictive behavior regards time estimation error as a temporal prediction error (PE), an independent variable that controls cognition, behavior, and learning. Based on this perspective, we investigated whether temporal PEs affect short-term memory scanning. Participants performed temporal predictions while they maintained information in memory. Model inference revealed that PEs affected memory scanning response time independently of the memory-set size effect. We discuss the results within the context of formal and mechanistic models of short-term memory scanning and predictive coding, a Bayes-based theory of brain function. We state the hypothesis that our finding could be associated with weak frontostriatal connections and weak striatal activity.

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