Qiulong Yang

Moving source localization with a single hydrophone using multipath time delays in the deep ocean

Localizing a source of radial movement at moderate range using a single hydrophone can be achieved in the reliable acoustic path by tracking the time delays between the direct and surface-reflected arrivals (D-SR time delays). The problem is defined as a joint estimation of the depth, initial range, and speed of the source, which are the state parameters for the extended Kalman filter (EKF). The D-SR time delays extracted from the autocorrelation functions are the measurements for the EKF. Experimental results using pseudorandom signals show that accurate localization results are achieved by offline iteration of the EKF.

A Simple Method for Source Depth Estimation with Multi-path Time Delay in Deep Ocean*

A method of source depth estimation based on the multi-path time delay difference is proposed. When the minimum time arrivals in all receiver depths are snapped to a certain time on time delay-depth plane, time delay arrivals of surface-bottom reflection and bottom-surface reflection intersect at the source depth. Two hydrophones deployed vertically with a certain interval are required at least. If the receiver depths are known, the pair of time delays can be used to estimate the source depth. With the proposed method the source depth can be estimated successfully in a moderate range in the deep ocean without complicated matched-field calculations in the simulations and experiments.

Analysis on the Characteristic of Cross-Correlated Field and Its Potential Application on Source Localization in Deep Water

The interference characteristics of cross-correlated broadband fields received by a single hydrophone deployed near the bottom at two different ranges are analyzed in this paper. The ray theory is used to derive the interference pattern, which is a combination of two kinds of interference phenomena. One kind of interference period contains the information of radial source velocity, and the other one is related to source depth. The source motion parameters, including the range and time of closet point of approach (CPA), constant source velocity and source depth, can be estimated by computing the Fourier transform of cross-correlated broadband fields when the existence of a CPA is apparent in the data. If the CPA is not evident, only the radial source velocity and the discrimination of surface versus submerged source can be provided. Note that the proposed method is a broadband technique. Experimental results confirm this single hydrophone estimation method of radial source velocity and source depth.

Spatial Vertical Directionality and Correlation of Low-Frequency Ambient Noise in Deep Ocean Direct-Arrival Zones

Wind-driven and distant shipping noise sources contribute to the total noise field in the deep ocean direct-arrival zones. Wind-driven and distant shipping noise sources may significantly and simultaneously affect the spatial characteristics of the total noise field to some extent. In this work, a ray approach and parabolic equation solution method were jointly utilized to model the low-frequency ambient noise field in a range-dependent deep ocean environment by considering their calculation accuracy and efficiency in near-field wind-driven and far-field distant shipping noise fields. The reanalysis databases of National Center of Environment Prediction (NCEP) and Volunteer Observation System (VOS) were used to model the ambient noise source intensity and distribution. Spatial vertical directionality and correlation were analyzed in three scenarios that correspond to three wind speed conditions. The noise field was dominated by distant shipping noise sources when the wind speed was less than 3 m/s, and then the spatial vertical directionality and vertical correlation of the total noise field were nearly consistent with those of distant shipping noise field. The total noise field was completely dominated by near field wind generated noise sources when the wind speed was greater than 12 m/s at 150 Hz, and then the spatial vertical correlation coefficient and directionality pattern of the total noise field was approximately consistent with that of the wind-driven noise field. The spatial characteristics of the total noise field for wind speeds between 3 m/s and 12 m/s were the weighted results of wind-driven and distant shipping noise fields. Furthermore, the spatial characteristics of low-frequency ambient noise field were compared with the classical Cron/Sherman deep water noise field coherence function. Simulation results with the described modeling method showed good agreement with the experimental measurement results based on the vertical line array deployed near the bottom in deep ocean direct-arrival zones.

A Method for Noise Source Levels Inversion with Underwater Ambient Noise Generated by Typhoon in Deep Ocean

Sea-surface wind agitation can be considered the dominant noise sources whose intensity relies on local wind speed during typhoon period. Noise source levels in previous researches may be unappreciated for all oceanic regions and should be corrected for modeling typhoon-generated ambient noise fields in deep ocean. This work describes the inversion of wind-driven noise source level based on a noise field model and experimental measurements, and the verification of the inverted noise source levels with experimental results during typhoon period. A method based on ray approach is presented for modeling underwater ambient noise fields generated by typhoons in deep ocean. Besides, acoustic field reciprocity is utilized to decrease the calculation amount in modeling ambient noise field. What is more, the depth dependence and the vertical directionality of noise field based on the modeling method and the Holland typhoon model are evaluated and analyzed in deep ocean. Furthermore, typhoons named “Soulik” in 2013...

Striation-based source depth estimation with a vertical line array in the deep ocean

A striation-based method with a vertical line array is proposed for source depth estimation. Broadband striation structures of direct and surface-reflected arrivals after propagating to receivers near the ocean bottom are applied. A tracking algorithm for the striation structures is proposed based on the extended Kalman filter. A cost function for source depth estimation is presented by matching the traces of the measured striations with a library of model-based traces under different source depths. The method is demonstrated on array data collected during an acoustic research experiment in the South China Sea in 2016.

Depth-dependence and vertical directionality of wind-driven ambient noise in deep ocean

The received wind driven noise field can be described as a sum of fields radiated from many random sources on the sea surface. Wind driven noise source levels can be modeled by empirical relationship with local wind speed. A method for modeling wind-driven ambient noise based on ray approach in deep ocean is presented. Simulations are performed to demonstrate the validity of the method. The wind-driven ambient noises are attributed to not only the near noise sources but also distant noise sources. The depth dependence and vertical directionality of ambient noise caused by wind agitation are analyzed by using the proposed modeling method, and vertical directionality frequency dependence is also described. In addition, the relationship between the logarithm of wind speed and noise levels is also analyzed at near surface and bottom depth. The power of wind speed with respect to received noise levels is equal to that of wind speed with respect to noise source levels approximately.

Numerical modeling of sound propagation through the internal soliton waves over continental slope

The internal solitary waves propagating over the shelf slope fluctuating the acoustic energy in shallow water has been widely studied. In this paper, this process is broadened into the continental slope with different gradient at different range which is linked with the shallow water and the deep water. The temporal and spatial structures of the acoustic field with the internal solitary wave passing through continental shelf to the deep region are analyzed. The variation of signal intensity at the receiver, which is caused by the moving soliton and space dependent bathymetry, shows the coupling between low modes and high modes. The location of the internal soliton waves relative to the source and the gradient of the continental slope are considered as the dominant factors fluctuating the acoustic energy received at a range of 15km by simulating the individual and joint effect of the soliton and bathymetry on the coupling coefficients.

Model-independent depth classification of transient acoustic signal in deep water

A method of estimating the source depth of wideband underwater acoustic pulses in deep water is proposed in this paper. The method is based on the characteristic of frequency domain interference oscillation of broadband signals received at a single stationary hydrophone. The oscillation period is related to the Lloyds Mirror effect (LME) and can be transformed into the information of source depth with the known source range. If the source range is uncertain, one can distinguish the submerged source from the near-surface one according to the sensitivity of estimated source depth versus source range. Experimental results confirm this source depth classification method.

Multipath-based passive source range localization with a single hydrophone in deep ocean

This paper presents a single-hydrophone based method for source range localization from information contained in the multipath propagation in the reliable acoustic path (RAP) environment. The time delays between the direct (D) and the surface-reflected (SR) arrivals are obtained from the autocorrelation of the received signal and are compared with the D-SR time delays predicted by the acoustic model. Because of the high bottom-reflection loss and uncertainty of bottom properties, only the D-SR time delays are robust information for source localization. If the source depth is assumed known, the D-SR time delays versus source range can be predicted by the acoustic model. Reliable source track is then given through a family of measurements of the estimated source range during a period of time. Experimental data from a sea trial in South China Sea show that a sound source emitting 700-1500 Hz LFM sweeps could effectively be located within a range of 13km. The proposed method may be of advantage to source localization due to its simplicity.