UACE2017 Proceedings: Measurement errors in ultrasonic Doppler devices caused by variation in the speed of sound along the propagation path

• Session:
  Sonar performance modeling and verification - Applications to active and passive sonar
• Paper:
  Measurement errors in ultrasonic Doppler devices caused by variation in the speed of sound along the propagation path
• Author(s):
  Shokichi Tanaka, Hideyuki Nomura, Tomoo Kamakura
• Abstract:
  Underwater ultrasonic devices applying Doppler effects, such as Doppler sonar and acoustic Doppler current profiler (ADCP) conventionally use a constant sound speed as the average speed. However, because the sound speed in the sea varies with the water depth, the assumed constant sound speed has the potential to cause measuring errors. Accordingly, we have investigated the influence of the sound speed and the sea current on the Doppler effects and derived the equations of Doppler shift by taking into account those that are dependent of the propagation path so far. In this report, the measuring errors caused by the assumption of constant sound speed in the conventional Doppler shift equation ?fold =2f(vs-vt)/cav are described on the basis of the derived improved Doppler shift equation?fnew =2f(vs/cs-vt/ct). Here, f, vs, vt, cav, cs and ct are denoted as the transmitted frequency, the moving speed of the source, the moving speed of the target, the average sound speed, the sound speed around the source and the sound speed around the target, respectively.By comparing ?fold and ?fnew, the measuring errors occurring in ?fold were evaluated. When cav, vs, vt, cs and ct were individually assumed, the measuring errors of ?fold were numerically obtained.The measuring errors of vt being finally measured were calculated with a parameter A defined as ct/cs. As a result, it was found that the relative errors of vt are approximately proportional to A. It was also pointed out that these errors are one of the systematic errors in ultrasonic Doppler devices.
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Contact details

• Contact person:
  Mr Shokichi Tanaka
• e-mail:
  
• Affiliation:
  The University of Electro-Communications
• Country:
  Japan