Performance of PASA in ocean waveguides

Abstract

Passive Synthetic Aperture (PASA) is a technique of increasing the length of a small array artificially through array towing motion and signal processing. This will acquire the advantage of a long array while maintaining the maneuverability of short array. Therefore, it has better performance in multi-targets distinguishing and detection than the conventional physical aperture array. However, the performance of PASA is also strongly influenced by the horizontal correlation radius of the sound field. Theory analysis shows that only when the horizontal correlation radius of the sound field is much larger than the length of physical aperture array, the advantage of PASA can be obvious. In this paper, the performance of PASA is compared with physical aperture array in the ocean waveguide through the experiment data from the South China Sea in 2014. With the modified extended towed array method in beam-domain (BD-ETAM), a virtual array with 160 hydrophones (240 m) is synthesized by a physical array with 32 hydrophones (48 m). The result shows that when the horizontal correlation radius exceeds 240 m, the processing gain of the synthesized virtual array with 160 hydrophones is higher than the physical array with 32 hydrophones by 9.5 dB. When the horizontal correlation radius is less than 30 m, the processing gain of the synthesized virtual array with 160 hydrophones is only higher than the physical array with 32 hydrophones by 6 dB. Furthermore, the detection performance of the synthesized virtual array is almost the same as the physical array in such case. That is to say, because the horizontal correlation radius of the sound field is short in the shadow zone of the ocean waveguide, the performance of PASA is limited to near the conventional physical aperture array. In contrast, the performance of PASA is remarkable better than the conventional physical aperture array in the convergence zone of the ocean waveguide since the horizontal correlation radius is large.