Synthetic head-wave correlations from ocean ambient noise on a drifting vertical line array.

Head-wave correlations from ocean surface noise have been identified through simulations and experiments using vertical and horizontal arrays. Previous studies have shown that most head-wave correlations were derived from averaging only a few minutes of surface noise, with the receiving array effectively in a fixed position. However, whether these "weak" head-wave correlations can be observed at different locations and times, and under what conditions they occur, remains uncertain. This study analyzes head-wave correlations at four representative time points with varying surface noise power levels, synthetic head-wave correlations at the water-sediment critical angle, and passive fathometer returns over a 13-h drift (6 km) using BOUNDARY2003 data from a vertical line array. The presence of these signal types depends on the energy of stationary phase noise sources, which varies with frequency and time, as shown by conventional beamforming output. Synthetic head-wave correlations originating from the water-sediment interface are detected along nearly the entire drift track, with frequency-dependent variations noted. The robustness of synthetic head-wave correlations offers an effective method for estimating waveguide and geoacoustic parameters over large areas, significantly enhancing environmental characterization efforts.