Abstract
Three cruises with shipboard Acoustic Doppler Current Profiler (ADCP) were performed along a transect across the Peng-hu Channel (PHC) in the Taiwan Strait during 2003-2004 in order to investigate the feasibility and accuracy of the phase-averaging method to eliminate tidal components from shipboard ADCP measurement of currents. In each cruise measurement was repeated a number of times along the transect with a specified time lag of either 5, 6.21, or 8 hr, and the repeated data at the same location were averaged to eliminate the tidal currents; this is the so-called ”phase-averaging method”. We employed 5-phase-averaging, 4-phase-averaging, 3-phase-averaging, and 2-phase-averaging methods in this study. The residual currents and volume transport of the PHC derived from various phase-averaging methods were intercompared and were also compared with results of the least-square harmonic reduction method proposed by Simpson et al. (1990) and the least-square interpolation method using Gaussian function (Wang et al. 2004). The estimated uncertainty of the residual flow through the PHC derived from the 5-phase-averaging, 4-phase-averaging, 3-phase-averaging, and 2-phase-averaging methods is 0.3, 0.3, 1.3, and 4.6 cm s-1, respectively. Procedures for choosing a best phase average method to remove tidal currents in any particular region are also suggested.
Highlights
Shipboard Acoustic Doppler Current Profiler (ADCP) has been used extensively to measure three-dimensional flow structures and their vertical profiles in oceans for over twenty years
This method is sometimes termed as the “phase-averaging method” because the repeated measurements are designed to be at some specified phases of the semidiurnal or diurnal tidal cycle
A similar but simpler approach was used in the Taiwan Strait to eliminate only dominant semidiurnal tidal currents by making two repeated current measurements along the same transect with the time separation being 6 hr and 12 min (Liu et al 2000; Jan and Chao 2003)
Summary
Shipboard Acoustic Doppler Current Profiler (ADCP) has been used extensively to measure three-dimensional flow structures and their vertical profiles in oceans for over twenty years. Katoh et al (1996, 2000) first applied this method to remove diurnal and semidiurnal tidal flows from observed flows by performing four round-trip ADCP surveys along each transect during a diurnal tidal period of 24 hr and 50 min This method is referred to as “4R-phase-averaging method” in this study. A similar but simpler approach was used in the Taiwan Strait to eliminate only dominant semidiurnal tidal currents by making two repeated current measurements along the same transect with the time separation being 6 hr and 12 min (Liu et al 2000; Jan and Chao 2003) It is termed the “2-phase-averaging method” in this study. Details of these phase-averaging methods will be described in a later section
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
