Matched-field localization using a virtual time-reversal processing method in shallow water

Abstract

Time-reversal processing (TRP) is an implementation of matched-field processing (MFP) where the ocean itself is used to construct the replica field. This paper introduces virtual time-reversal processing (VTRP) that is implemented electronically at a receiver array and simulates the kind of processing that would be done by an actual TRP during the reciprocal propagation stage. MFP is a forward propagation process, while VTRP is a back-propagation process, which exploits the properties of reciprocity and superposition and is realized by weighting the replica surface with the complex conjugate of the data received on the corresponding element, followed by summation of the processed received data. The number of parabolic equation computational grids of VTRP is much smaller than that of MFP in a range-dependent waveguide. As a result, the localization surface of VTRP can be formed faster than its MFP counterpart in a range-dependent waveguide. The performance of VTRP for source localization is validated through numerical simulations and data from the Mediterranean Sea. Time-reversal processing (TRP) [1][2][3][4][5][6][7] is a process of retransmitting a received signal in a time-reversed fashion by a source-receiver array. In the frequency domain, time reversal is equivalent to phase conjugation. When TRP is applied to source localization, known as virtual time-reversal processing (VTRP), it is unnecessary to send a signal back and forth between the source and receiver. Instead, assuming that the acoustic channel is sufficiently stable in time, the retransmission of the temporal dispersed signals in a time reversed fashion will be done by a computer. A passive array is used in VTRP instead of a source-receiver array.When TRP is applied to source localization, there is one drawback to this back-propagation approach. Because of sound attenuation, the acoustic intensity close to the "source-receiver" array is much stronger than the focusing peak at the real source location. This means that the focusing peak is only a local maximum around the real source *Corresponding author (email: walternwpu@gmail.com) location rather than a global one. To suppress the stronger peaks close to the passive array and make the focusing peak the global maximum, an appropriate normalization factor should be introduced to the back-propagation field. Therefore, the localization surface formed by VTRP contains the focusing peak, which provides the greatest likelihood of the source location.Matched-field processing (MFP) and VTRP are conceptually similar, but differ in their physical meaning and physical implementation. MFP [8-13] is a forward propagation process that consists of systematically placing a test point source at each point of a search grid, computing the replica vectors on the array and then correlating these replicas with the data from the real source. A search is performed in a region of possible target positions. VTRP is a back-propagation process which exploits the properties of medium reciprocity and superposition. VTRP ca...

Underwater Sound Source Localization Based on Passive Time-Reversal Mirror and Ray Theory

“…Notably, Table 1 indicates that the percentage of the range error decreased when the range increased; however, the percentage of the depth error and the average value of did not change in response to changes in the source location or sound frequency. The results obtained from the towing tank experiments revealed that with only four hydrophones and an aperture (i.e., the interval between hydrophones) of 0.5 m in the TRM, relative to the results of previous experiments in which more than 20 hydrophones were usually used [ 21 , 26 , 32 ], the present passive TRM configuration combined with the AcTUP allowed for reasonably accurate source locations to be obtained. Through their numerical simulations, Sun [ 48 ] and Chen [ 49 ] demonstrated that an increase in the number of TRM elements and TRM’s aperture resulted in higher sound pressure at the retro-focused location.…”

“…Normal model modeling was used to explain the aforementioned finding. Zhang et al [ 26 ] introduced virtual time-reversing processing (VTRP) for source localization in shallow water. For VTRP, they used a passive array instead of a source-receiver array.…”

“…According to the aforementioned literature review, for underwater sound source-localization, most studies used the normal mode model [ 25 , 32 ] and parabolic equation model [ 26 ] to describe sound propagation in the ocean. Few studies have examined the performance of a passive TRM based on ray theory in a real ocean environment.…”

A Three-Dimensional Target Depth-Resolution Method with a Single-Vector Sensor

“…Goldhahn [ 6 ] proposed a waveguide invariant depth classification method based on adaptive matched-filtering under uncertain environmental conditions. Matched field processing (MFP) [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ] is a generalized beamforming method which uses the spatial complexities of acoustic fields in an ocean waveguide to estimate the range, depth and azimuth of targets.…”

Application and Extension of Vertical Intensity Lower-Mode in Methods for Target Depth-Resolution with a Single-Vector Sensor

“…Goldhahn [ 20 ] proposed a method for depth classification based on waveguide invariant adaptive matched-filtering. Matched field processing (MFP) [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ] has also been widely used in depth estimation studies. Premus proposed a method for target depth discrimination based on matched subspace detector [ 29 , 30 ] and mode-filtering technology [ 31 ].…”