Forward scattering detection of a submerged object by a vertical hydrophone array

When an object crosses a source-receiver line, the resulting weak acoustic field aberration is often overwhelmed by a strong direct blast. In this study, a lake experiment with a vertical receiver array spanning the water column was designed and conducted with a 10 kHz pulse. The study aimed to detect the aberration caused by forward scattering from an intercepting submerged object. Although such aberration could be directly observed, it varies by only 3 dB, at most, around the direct blast. Hence, the vertical hydrophone array was subjected to time-delay beamforming, and a principal component analysis was conducted on the stable portion of the beam output. The second principal component was extracted from the horizontally directed beam output waveform at the vertical receiver array. The invariant direct blast component was reduced after analysis, and the field aberration caused by forward scattering of the submerged object was amplified by up to 10 dB above the background acoustic field.