Structure of interferogram and hologram of non-moving source in presence of shallow water internal waves

Abstract

The results of holographic signal processing of the oceanographic experiment SWARM-95 on the coast of New Jersey are presented in the paper. The used acoustic signals were obtained on stationary acoustic track (non-moving airgun source) in the presence of shallow water intensive internal waves (IIW). The IIW led to significant 3D acoustic effects [Badiey et al., JASA 117(2), 613–625]. Within framework of holographic signal processing [Pereselkov and Kuz’kin, JASA 151(2), 666–676] the source interferogram (sound intensity distributions in frequency-time coordinates) is analyzed by two-dimensional Fourier transform (2D-FT). The result of the 2D-FT is called the Fourier hologram (source hologram). In result of holographic signal processing, the two separated sets of spectral spots are obtained in hologram domain. The first set of spectral spots corresponds to sound field in nonperturbed waveguide (without of IIW). The second set of spectral spots in hologram corresponds to hydrodynamic field perturbation by IIW. This structure of the hologram allows the reconstruction of interferogram of nonperturbed field for waveguide in the absence of IIW. The error in the reconstruction of the nonperturbed interferogram is estimated. [Work supported by grant from the Russian Science Foundation 23-61-10024.]