A reliable acoustic path:Physical properties and a source localization method

The physical properties of a reliable acoustic path （RAP） are analysed and subsequently a weighted-subspace~ fitting matched field （WSF-MF） method for passive localization is presented by exploiting the properties of the RAP environment. The RAP is an important acoustic duct in the deep ocean, which occurs when the receiver is placed near the bottom where the sound velocity exceeds the maximum sound velocity in the vicinity of the surface. It is found that in the RAP environment the transmission loss is rather low and no blind zone of surveillance exists in a medium range. The ray theory is used to explain these phenomena. Furthermore, the analysis of the arrival structures shows that the source localization method based on arrival angle is feasible in this environment. However, the conventional methods suffer from the complicated and inaccurate estimation of the arrival angle. In this paper, a straightforward WSF-MF method is derived to exploit the information about the arrival angles indirectly. The method is to minimize the distance between the signal subspace and the spanned space by the array manifold in a finite range-depth space rather than the arrival-angle space. Simulations are performed to demonstrate the features of the method, and the results are explained by the arrival structures in the RAP environment.

Theoretical analysis on waveform structures of pulse propagating in shallow water with an ideal thermocline

In this paper, waveforms of band-limited signals are calculated under the assumptionof ideal thermocline by using the ray-mode theory with beam displacement (RMB). Comparison between the RMB approach and MOATL codes shows that the RMB approach is a fast and accurate one and the run time by the RMB approach is reduced by at least two orders of magnitude. Results reveal that the beam displacement plays a key role in waveform calculation under the condition of thermocline, and the validity on the formula of mode attenuation coefficient with beam displacement is further proved. The -dependencies of waveforms of pulse signals on source-receiver depths, transmission range, signal frequency, and bottom parameters are discussed.

Experimental study in correlation variation of acoustic propagation channel in Philippine sea

The variation of correlation in acousic propagation channel is mainly caused by the time-space variation of the acoustic channel's multipath structure. In general, there is little innuence from the sea bottom in deep sca, so the multipath structure of the acoustic channels is simple. Thus in deep sca it is not morc difficult to realize the correction match for the acoustic channel. In this experiment, a towed powerful low-frequency transducer is used to transmit linear frequency modulated pulse,and at the receiving terminal the copy-correlation and the pulse to pulse correlation are used to obtain the time-space variation of acoustic channel correlation. Because the broadband, long duration pulse and corresponding signal processing method are made use, the noise influence to the correlation is reduced as greatly as possible.Therefor our experimental results prove that the time-space correlation of acoustic channel is mainly determined by the time-space variation of channel's multipath structure, and coherent part of such a multipath channel makes up about 40 per cent of its total. Meanwhile the experimental results deseribed in this paper would be helpful to study thc correction match of the dcep sea acoustic channel.