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Best Methods for Obtaining Absolute Water Velocity Profiles from Gliders with ADCPs

  • Author(s): Ellis, Daniel Painter
  • Advisor(s): Washburn, Libe
  • et al.
Abstract

Autonomous underwater vehicles (AUVs) like gliders are typically used to obtain vertical cross sections of water properties along transects. Another, less common, application is the use of gliders as virtual moorings. Gliders offer many advantages compared with conventional moorings, but extensive evaluation of gliders as mooring substitutes has not been done.

Here, temperature and ocean current velocity data from coincidently deployed gliders-as- moorings and moorings are compared to assess the fidelity of glider-as-mooring data. The glider-as-mooring data were processed in a variety of ways and compared with mooring. During August 2012, two gliders sampled in a box pattern around a conventional mooring in 26 m water depth off of Pt. Sal, California for two and six days, respectively. Two box patterns were used, one 500 m on a side (two and four days) and the other 1 km on a side (two days). Temperature and velocity data from the gliders and moorings are compared using linear regressions and contouring techniques. Linear regressions show good agreement between glider and mooring temperatures (r2 = 0.89, p < 0.001). Significant correlations are also found between ADCP-derived velocities from the gliders and the mooring; along-shore velocities exhibit higher correlation (r2 = 0.70, p < 0.001) compared with cross-shore velocities (r2 = 0.37, p < 0.001). Glider versus glider comparisons are similar to glider versus mooring comparisons in the along-shore (r2 = 0.60, p < 0.001) and cross-shore (r2 = 0.36, p < 0.001) directions. Temperature comparisons between gliders also show good agreement (r2 = 0.93, p < 0.001 ).

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