UACE2017 Proceedings: Beam displacement and reflection images in the Bellhop Gaussian Beam Model

• Session:
  Sonar performance modeling and verification - Applications to active and passive sonar
• Paper:
  Beam displacement and reflection images in the Bellhop Gaussian Beam Model
• Author(s):
  Diana Mccammon, Dale Ellis
• Abstract:
  Transmission loss calculations with ray codes can be problematic, especially in range-dependent environments, so Gaussian beam methods are often a viable solution. However, the width of the Gaussian beams can introduce artifacts near the boundaries. Here we investigate the behaviour of the Bellhop Gaussian Beam Model when beam displacement terms and boundary reflection images are included. Beam displacement is a horizontal shift of the reflected ray at sub-critical angles from a hard bottom caused by phase delay of the reflection coefficient. Beam displacement primarily affects the phase of the field. Boundary reflection images augment the central ray with surface and bottom image beams and primarily affect the level of the field. The goal is to determine if these terms will improve the low-frequency, shallow-water performance of the Gaussian beam model. Our approach is to measure the validity of Bellhop’s Gaussian Beam Model predictions at water depth/wavelength (h/?) ratios smaller than the usually ascribed Bellhop limitation of h/? > 20 by comparing the resulting intensity predictions with a normal mode exact solution. The conclusion of this examination shows that the inclusion of beam displacement and boundary image beams does greatly enhance the low-frequency shallow water accuracy of Bellhop.
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Contact details

• Contact person:
  Dr Dale Ellis
• e-mail:
  
• Affiliation:
  Mount Allson University
• Country:
  Canada