{'fraction_non_alphanumeric': 0.014642549526270457, 'fraction_numerical': 0.0, 'mean_word_length': 4.696078431372549, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Passive acoustic inversion with virtual head waves

A passive acoustic inversion method with virtual head waves extracted from ocean surface noise is presented. The noise is assumed to be coming from the sea-surface due to wind and waves and a vertical array is used to produce beamformed time-series. Cross-correlating a beam steered downward with one steered upward at the same angle produces virtual head waves with periodic peaks in the time-series but only for the beams steered at the seabed critical angle. The virtual head wave has the same phase speed as the real head wave, but travel time is offset, thus virtual. It has been attributed to the cross-correlation between head waves and head waves or head waves and perfect reflections. With two of the virtual head wave travel times and the critical angle, an inverse method is developed to extract the water depth, water column and seabed sound speeds as well as the array depth. The theory is developed for the expected travel times and this provides the basis for the inversion methodology. Both the theoretical framework and the inversion method will be presented along with illustrating examples.