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Improving Acoustic Doppler Current Profiler Accuracy with Wide-Area Differential GPS and Adaptive Smoothing of Ship Velocity

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  • Accurate ship velocity is important for determining absolute currents from acoustic Doppler current profiler (ADCP) measurements. In this paper, the authors describe the application of two methods to improve the quality of ship velocity estimates. The first uses wide-area differential global positioning system (WADGPS) navigation to improve ship positioning. During the cruise, raw global positioning system (GPS) pseudorange data are collected. The pseudorange measurement is the difference between satellite transmission time and receiver reception time of a GPS signal. A few days after the cruise, satellite clock corrections from the Canadian Active Control System and orbital parameters from the U.S. Coast Guard Navigation Center are used to derive WADGPS positions that remove the position degradation effects of selective availability. Two-dimensional root-mean-square (rms) position accuracies reduce from ±34 to ±9 m. The authors’ second method of improving the ship velocity applies an adaptive local third-order polynomial smoother to the raw ship velocities. This smoothing method is particularly effective at handling the nonstationary nature of the signal when the ship is starting, stopping, or turning, which is typical of oceanographic cruises. Application of the smoother in this case reduces overall rms noise in the ship velocity by 16%. The combination of both methods reduces the uncertainty due to navigation of a 20-min ADCP absolute velocity from ±0.063 to ±0.038 m s⁻¹—a 40% reduction. These methods also improve the calibration for sensitivity error and ADCP–gyrocompass misalignment angle.
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  • Pierce, Stephen D., John A. Barth, Robert L. Smith, 1999: Improving Acoustic Doppler Current Profiler Accuracy with Wide-Area Differential GPS and Adaptive Smoothing of Ship Velocity. Journal of Atmospheric and Oceanic Technology, 16, 591–596
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  • 16
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  • 5
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  • The Coastal Jet Separation project was funded by the National Science Foundation Grant OCE-9314370. Additional support was provided by the Office of Naval Research Grants N00014-91-J-1242 andN00014-95-1-0382.
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