The detection of tonal signals with unknown frequencies is an important area of study in underwater signal processing. A common approach to address this issue is to use the Discrete Fourier Transform (DFT) for observations. When a tone does not lie precisely at the discrete DFT frequency point, its energy will leak to adjacent frequency point. This phenomenon is known as scalloping loss or Picket Fence Effect (PFE). PFE leads to the degradation of detection performance based on DFT. This paper studies the problem of robust detection in the case of PFE. A coherently-averaged power processor utilizing the information of adjacent frequency bins is designed. The results of simulations and experiments show that the proposed method is robust against PFE, and is highly suitable for tone detection in practical circumstances.
We demonstrated that the feats of the dolphin biosonar system can be achieved through physical implementation. Numerical and experimental results suggested that dolphins have evolved to intelligently manipulate physical laws. Gradient distributions of sound speed and density in the forehead counterpart can enhance the main beam by gathering more sound energy to reinforce the main beam and lowering side lobes. As dolphins prove to accomplish efficient control on their biosonar capabilities in multiple ways, this paper provides an additional aspect to enrich our understanding of how one of the best natural biosonar systems works and build a step to inspire additional advanced sound control systems.
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