Broadband passive aperture extension based on non-uniform horizontal array in shallow water

In order to research and apply the low frequency acoustic physics in shallow water, broadband signal of a large aperture horizontal array is required. Unfortunately, a large aperture array is expensive and difficult to place, and so it is expected to use aperture extension technique with a short array to get a large aperture array signal. Most existing passive aperture extension methods are based on towed uniform linear array at a constant speed and coherent narrowband continuous signal. They are not applicable to the cases of non-uniform array and discontinuous broadband source signal. To solve these issues, passive aperture extension method based on non-uniform horizontal array and broadband signal is proposed. Instead of a towed linear array, a static seafloor-deployed non-uniform horizontal array is used to receive broadband source signal, which is moving horizontally and launched repeatedly. After uniform interpolation in space, broadband signal passive aperture extension technique in element domain or beam domain is used to produce signal of a large virtual aperture array. In shallow-water waveguide with depth of about 70 m, the 20~200 Hz signal received by 2 elements, whose longitudinal space is 27.5 m, are processed by linear interpolation method. Simulation and experiment results show that the correlation coefficients between the signals produced by interpolation and the real ones are greater than 0.99, which verifies the rationality of the proposed interpolation method. Dispersion characteristics of the normal modes can be identified by the broadband passive aperture extension in beam domain or element domain with the extended aperture greater than 1 km, but cannot be identified by conventional beamforming with a short array aperture of 250 m, which verified the effectiveness of the proposed method. © 2021 Acta Acustica.