UACE2017 Proceedings: Modelling of an echo-signal from a target in a waveguide with positive sound speed gradient

• Session:
  Target Echo Strength-Measurements and Modelling
• Paper:
  Modelling of an echo-signal from a target in a waveguide with positive sound speed gradient
• Author(s):
  Natalie Grigorieva, Mikhail Kupriyanov, Sergey Kadyrov
• Abstract:
  Target echo-strength measurements and modelling are usually made in a perfect enviroment where the sound speed of the surrounding medium is constant. In addition it is supposed that the object under study is in a free space. These ideal conditions never happen in reality. Most of the time the target to be detected is submerged in a waveguide where the sound speed is a function of depth. In present paper we study how both these additional conditions modify the acoustic scattering of a spherical target. To simlify the approach, we have considered a medium model where the scatterer as well as the sound source/receiver are located in a homogeneous water layer. Below this layer the sound speed increases with depth and the reflection coefficient squared changes linearly. For calculation the echo-signal in the frequency domain we have followed the Hackman and Sammelmann's general approach. The arising scattering coefficients of the sphere were evaluated with the use of the normal mode method. The amount of normal modes forming the backscattered field is determined by the given directivity of the source. The emitted signal is a pulse with a cosine envelope and a pulse duration equal to 0.01 s. Computational results are obtained in a wide frequency range 70 - 90 kHz, distances between the source/receiver and a target from 500 m up to 1 km. A target is assumed to be acoustically rigid with a radius of 0.3 - 0.5 m. The effect on a target echo-strength of the ray paths which contribute to the scattering process as well as the surface wave of the Franz type has been studied. [This work was supported by the Russian Ministry of Education and Science through Grant No 02.G25.31.01.0149 dateed 01.12.2015].
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Contact details

• Contact person:
  Prof Natalie Grigorieva
• e-mail:
  
• Affiliation:
  D.Sc., Professor
• Country:
  Russian Federation