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Ensuring Accurate Acoustic Wave Systems: Common Errors & Solutions

Environmental factors can introduce errors in acoustic wave systems. Transducer orientation, water clarity, aeration, vessel trim, ocean currents, sea state, temperature profile, and pitch and trim can impact accuracy. Solutions include proper transducer siting, JANNUS configuration, temperature sensors, and reducing side lobe errors. Understanding these errors is crucial for maintaining the precision of acoustic wave-based systems.

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Ensuring Accurate Acoustic Wave Systems: Common Errors & Solutions

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  1. ERRORS • Environmental factors can introduce errors in any system that relies for its operation on the transmission and reception of acoustic waves in salt water. • Errors in Transducer Orientation: The transducers should make a perfect angle of 60deg with respect to the keel or else the speed indicated will be inaccurate.

  2. ERRORS • WATER CLARITY : • In exceptional cases the purity of the sea water may lead to insufficient scattering of the acoustic energy and prevent an adequate signal return. • It is not likely to be a significant factor because most sea water holds the suspended and micro organisms that adequately scatter an acoustic beam.

  3. ERRORS • AERATION : • Aerated water bubbles beneath the transducer face may reflect acoustic energy of sufficient strength to be interpreted erroneously as sea bottom returns producing inaccurate depth indications and reduced speed accuracy. • Proper siting of the transducer, away from bow thrusters will reduce this error.

  4. ERRORS • VESSEL TRIM AND LIST : • A change in the vessel’s trim from the calibrated normal will affect fore / aft speed and an excessive list will affect atwartship speed. • A JANNUS CONFIGURATION transducer reduces this error.

  5. ERRORS • OCEAN CURRENT PROFILE : • This effect is prevelant in areas with strong tides or ocean currents. • In the water track mode, a speed log measures velocity to multiple layers several feet down in the water. • If these layers are moving in opposite directions to the surface water, an error will be introduced.

  6. ERRORS • SEA STATE : • Following seas may result in a change in the speed indication in the fore-aft and port-stbd line depending upon the approaching sea relative to the ship’s axis.

  7. ERRORS • TEMPERATURE PROFILE : • The temperature of the sea water affects the velocity of the propogated acoustic wave. • Temperature sensors are included in the transducer to produce corrective data.

  8. ERRORS • PITCH & TRIM : • Varying angles of pitch or trim from the horizontal introduce a small error factor. • This error cannot be corrected, however such errors are negligible. • The problem of heaving (vertical acceleration ) can be significant causing an additional error factor. • This factor can be cancelled out by using JANNUS CONFIGURATION.

  9. Side lobe Error • When the side lobe reception dominated over the main beam reception, there will be an error in the speed indicated. • This error is more pronounced on a sloppy bottom, where the side lobe will be reflected at a more favorable angle and will have path lengths less than the main beam. • The error can be reduced by reducing the beam of the transmitted acoustic wave.

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