UACE2017 Proceedings: Twinkling in Sonar Systems

• Session:
  Sonar Systems
• Paper:
  Twinkling in Sonar Systems
• Author(s):
  Peter Dobbins
• Abstract:
  Turbulence and other inhomogeneities in the water column cause fluctuations in propagating acoustic signals in the same way that turbulence in the interstellar medium causes stars to twinkle. The amplitude fluctuations bring about signal fading and failure to detect targets well within the theoretical range of the system. Phase fluctuations, however, cause loss of directivity and angular resolution in receiving arrays, spreading of transmitted beams, variations in the apparent arrival direction of signals and fluctuations in their arrival time. Fluctuations also result in an occasional high peak in the signal amplitude, allowing sources or targets to be detected at ranges much greater than predicted by the conventional sonar equation. This paper examines two approaches to predicting the probability of such signal peaks. The first is taken from astronomy and models the underwater medium as a random phase changing screen, or sequence of phase screens separated by a distance equivalent to the width corresponding to the length scale at which the medium remains correlated. The second approach is to apply catastrophe theory to look at how regions of high amplitude move in space. For example, the surface of a swimming pool focuses the light above it to form bright lines on the bottom, known as caustics. These patterns move in time and space following the random variations occurring at the surface. The predictions of these two theories will be compared, and estimates made of the increase in detection range that might be obtained using these occasional high peaks in any realistic scenario.
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Contact details

• Contact person:
  Dr Peter Dobbins
• e-mail:
  
• Affiliation:
  Consultant
• Country:
  United Kingdom