A Time-Frequency Joint Time-Delay Difference Estimation Method for Signal Enhancement in the Distorted towed Hydrophone Array

Abstract

To acquire the enhanced underwater ship-radiated noise signal in the presence of array shape distortion in a passive sonar system, the phase difference of the line-spectrum component in ship-radiated noise is often exploited to estimate the time-delay difference for the beamforming-based signal enhancement. However, the time-delay difference estimation performance drastically degrades with decreases of the signal-to-noise ratio (SNR) of the line-spectrum component. Meanwhile, although the time-delay difference estimation performance of the high-frequency line-spectrum components is generally superior to that of the low-frequency one, the phase difference measurements of the high-frequency line-spectrum component often easily encounter the issue of modulus 2π ambiguity. To address the above issues, a novel time-frequency joint time-delay difference estimation method is proposed in this paper. The proposed method establishes a data-driven hidden Markov model with robustness to phase difference ambiguity by fully exploiting the underlying property of slowly changing the time-delay difference over time. Thus, the phase difference measurements available for time-delay difference estimation are extended from that of low-frequency line-spectrum components in a single frame to that of all detected line-spectrum components in multiple frames. By jointly taking advantage of the phase difference measurements in both time and frequency dimensions, the proposed method can acquire enhanced time-delay difference estimates even in a low SNR case. Both simulation and at-sea experimental results have demonstrated the effectiveness of the proposed method.

A Nonlinear Data-Driven Towed Array Shape Estimation Method Using Passive Underwater Acoustic Data

“…Unlike the methods in [26][27][28], where only phase information of the detected narrowband components is used to estimate time-delay differences, the complex narrow-band components including both amplitudes and phases would be exploited to acquire enhanced time-delay estimates in the paper. The benefits of the complex values lie in two aspects: on the one hand, although the information of time delays is involved only in the phases, the corresponding amplitudes can represent the credibility and stability of these phases, therefore, the joint exploitation of both the phase and amplitude information would provide a better way for the improvement of the time-delay estimation compared to those methods with only the use of the phase information.…”

“…In addition, the limited precision of these auxiliary sensors makes it difficult to accurately estimate the array shape in real-time application [9,10]. The source-dependent methods, in essence, measure the relative time or phase delays among sensors by using one or more sources with known or unknown directions based on underwater acoustic data [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The single and double near-field source-dependent method is used for towed array shape estimation [11].…”

“…The phase of the narrow-band frequency in the passive acoustic data, which involves the information of time delays in the presence of array distortion, can be used to perform the array shape estimation. The phases in the multiple narrow-band frequencies from directional radiated noise source signals as sources of opportunity were used to acquire time-delay estimation [26]; an improved time-delay estimation method based on the phases of multiple narrow-band frequencies is developed by exploiting the underlying properties of slowly changing time-delay difference in the hydrophone array [27]; furthermore, the time-delay estimation method based on the phases of multiple narrow-band frequencies was developed for the improvement of hydrophone array estimation by exploiting the underlying properties of slowly-changing time-delay difference over time, and the Chinese remainder theorem technique is used to effectively address the phase difference ambiguity issue [28]. However, the proposed method directly uses the complex values of the detected narrow-band frequencies for the time-delay difference estimation, and effectively avoids the issue of the phase-difference ambiguity issue, which often occurs in the phase extraction operator, especially in the low signal-to-noise-ratio (SNR) case.…”

“…Considering the fact that the radiated noise sources have an amount of narrow-band components that originated from the vibration of mechanical equipment, we carry out the narrow-band detection for the acquisition of the information of time delays after beamforming-based signal enhancement in the hypothetical uniform linear array shape. Unlike these methods in [26][27][28], where only phase information of the multiple narrow-band frequencies is exploited to perform the time-delay estimation, a nonlinear ORPF method is proposed to acquire improved estimates of time delays by jointly exploiting the amplitude and phases of detected multiple narrow-band frequencies, and the posterior probability distribution inference is provided based on the expectationmaximization technique. The proposed scheme fully exploits the directional radiated noise source signals as sources of opportunity for online array shape estimation, and thus it requires neither the number nor direction of sources to be known in advance.…”

Spatial Spectral Enhancement of Broadband Signals in a Towed Array Using Deconvolved Subband Peak Energy Detection

“…Calibrating source-dependent method estimate array shapes can be conducted by processing known sound sources [21]. The disadvantages of these array shape estimation methods are that implementation is complicated, and the computational complexity is high, making real-time application difficult [22].…”