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On Sampling Strategies and Interpolation Schemes for Satellite-Tracked Drifters

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  • 1 Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia, Canada
  • | 2 Institute of Ocean Sciences, Sidney, British Columbia, Canada
  • | 3 Channel Consulting, Victoria, British Columbia, Canada
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Abstract

The effects of reduced sampling schedules (duty cycles) on velocity statistics derived from satellite-tracked drifters in the northeast Pacific Ocean are investigated. Continuous segments of the drifter records (in which all available satellite positions fixes are recorded and processed by Service ARGOS) are degraded to match the standard duty cycle used in the World Ocean Circulation Experiment–Surface Velocity Program, in which there are 48 h of no data transmission followed by 24 h of received transmission (48–24 h). Also examined are duty cycles of 32–16 h and 16–8 h. It is found that the strong inertial motions prevalent in the drifter records result in significantly biased statistics derived from the degraded series. Reproduction of the original prime (mean and standard deviation) and rotary spectral statistics requires an interpolation that takes into account the oscillatory component of the drifter motions. Duty cycles having shorter but more frequent gaps (e.g., 16–8 h) are not sufficient to resolve the main features of the flow. The authors recommend that interpolations over duty cycle segments of drifter records be customized to account for the dominant modes of variability observed in available continuous segments.

Corresponding author address: Steven Bograd, Scripps Institution of Oceanography, Mail Code 0230, 9500 Gilman Drive, University of California, San Diego, La Jolla, CA 92093-0230.

Email: bograd@bowfell.ucsd.edu

Abstract

The effects of reduced sampling schedules (duty cycles) on velocity statistics derived from satellite-tracked drifters in the northeast Pacific Ocean are investigated. Continuous segments of the drifter records (in which all available satellite positions fixes are recorded and processed by Service ARGOS) are degraded to match the standard duty cycle used in the World Ocean Circulation Experiment–Surface Velocity Program, in which there are 48 h of no data transmission followed by 24 h of received transmission (48–24 h). Also examined are duty cycles of 32–16 h and 16–8 h. It is found that the strong inertial motions prevalent in the drifter records result in significantly biased statistics derived from the degraded series. Reproduction of the original prime (mean and standard deviation) and rotary spectral statistics requires an interpolation that takes into account the oscillatory component of the drifter motions. Duty cycles having shorter but more frequent gaps (e.g., 16–8 h) are not sufficient to resolve the main features of the flow. The authors recommend that interpolations over duty cycle segments of drifter records be customized to account for the dominant modes of variability observed in available continuous segments.

Corresponding author address: Steven Bograd, Scripps Institution of Oceanography, Mail Code 0230, 9500 Gilman Drive, University of California, San Diego, La Jolla, CA 92093-0230.

Email: bograd@bowfell.ucsd.edu

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