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

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-meansquare (rms) position accuracies reduce from 634 to 69 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 60.063 to 60.038 m s21—a 40% reduction. These methods also improve the calibration for sensitivity error and ADCP‐gyrocompass misalignment angle.

[1]  Robert L. Smith,et al.  A separating coastal upwelling jet at Cape Blanco, Oregon and its connection to the California Current System , 2000 .

[2]  G. Terrell.  Statistical theory and computational aspects of smoothing , 1997 .

[3]  George O. Marmorino,et al.  Calibrating a Gyrocompass Using ADCP and DGPS Data , 1997 .

[4]  Robert L. Smith,et al.  Acoustic Doppler current profiler observations during the coastal jet separation project on R/V Wecoma, 17-27 August 1995 , 1997 .

[5]  John A. Barth,et al.  A Lagrangian drifter with inexpensive wide area differential GPS positioning , 1996, OCEANS 96 MTS/IEEE Conference Proceedings. The Coastal Ocean - Prospects for the 21st Century.

[6]  W. Härdle,et al.  Statistical Theory and Computational Aspects of Smoothing , 1996 .

[7]  W. Härdle,et al.  Statistical theory and computational aspects of smoothing : proceedings of the COMPSTAT '94 Satellite Meeting held in Semmering, Austria, 27-28 August 1994 , 1996 .

[8]  W. Cleveland,et al.  Smoothing by Local Regression: Principles and Methods , 1996 .

[9]  E. Firing,et al.  Processing ADCP data with the CODAS software system version 3.1 , 1995 .

[10]  Jianqing Fan,et al.  Local polynomial modelling and its applications , 1994 .

[11]  B. Hofmann-Wellenhof,et al.  Global Positioning System , 1992 .

[12]  Bernhard Hofmann-Wellenhof,et al.  Global Positioning System , 1992 .

[13]  Terrence M. Joyce,et al.  On in situ 'calibration' of shipboard ADCPs , 1989 .

[14]  A. Leetmaa,et al.  Acoustic Doppler current profiling in the equatorial Pacific in 1984 , 1988 .

[15]  W. Cleveland.  Robust Locally Weighted Regression and Smoothing Scatterplots , 1979 .

[16]  John Spencer.  GRADUATION OF A SICKNESS TABLE BY MAKEHAM'S HYPOTHESIS , 2022 .

[17]  W. S. B. Woolhouse,et al.  Explanation of a New Method of Adjusting Mortality Tables, with some observations upon Mr. Makeham's modification of Gompertz's Theory , 1870 .