Understanding the near-surface current is essential to estimating upper-ocean material transport. Wind forcing and wave motions are dominant in the near-surface layer, where the highly sheared flows can differ greatly from those at depth. A study, conducted by Nathan J.M. Laxague, Brian K. Haus, David G. Ortiz-Suslow, Conor J. Smith, Guillaume Novelli, Hanjing Dai, Tamay Özgökmen, and Hans C. Graber, displays a new method for remotely measuring the directional wind and wave drift current profile near the surface. Their work follows the spectral analysis of high spatial (~0.002 m) and temporal resolution (60 Hz) wave slope images, allowing for the evaluation of near-surface current characteristics without having to rely on instruments that may disturb the flow. FluxData’s FD-1665 Polarimetric imaging system was used as part of the research.
 
The shape of near-surface current profile has been the subject of scientific inquiry for many years due to the direct impact it has on things such as: radar remote sensing, oceanic material transport, etc. The classic approach to estimating such has been to parameterize the current as aligned with the wind velocity, with the magnitude given as a strict percentage of the 10-m neutral wind speed or friction velocity.
 
Advances in computer vision technology in recent years have allowed for the evaluation of the spatiotemporal characteristics that define the short high-frequency waves that are especially affected by near-surface current.
 
Observations were performed in both the Air-Sea Interaction Saltwater Tank (ASIST) at the University of Miami’s Surge-Structure-Atmosphere Interaction (SUSTAIN) facility and the mouth of the Columbia River (MCR) along the Oregon-Washington border. For the laboratory observations, near-surface dye tracking was employed to provide a standard for Lagrangian fluid transport speed. For the field observations, FluxData’s FD-1665 polarimetric camera was mounted off the starboard bow and oriented such that it imaged an area forward and away from the ship’s wake zone.
 
 
 
     The polarimetric camera was positioned 2.47m above the mean water level
    and oriented 45° below the horizontal, with the footprint centered at 5-m fetch.
 
 

The method provided short-scale temporal and spatial information from waves without disturbing the near-interface flows that define them. The polarimeter used was FluxData’s FD-1665, a system enclosing a beamsplitter and three Basler Scout series charge-coupled devices (CCDs), each of which acquires images composed of visible light in one of the following three linear polarization states: 0°, 45°, and 90°.
 
Real-time footage captured with FluxData's polarimetric imaging system:
 
Sea surface reconstruction of a still image (all dimensions in meters)
 
 
 
 
 
Time series of a water surface reconstruction from data
 
 
 
Near-surface currents are critical in the estimation of oceanic material transports-- especially of ecologically damaging materials of spilled oil or marine debris. Based on this research alone, future parameterizations of marine transport would benefit greatly from considering the magnitude and direction of ocean-atmosphere momentum flux. Currently, this method is being applied and includes a variety of shipboard, airborne, and drifting instruments for a more thorough investigation of the small-scale dynamics.
 
Ultimately, this new technique offers previously unavailable information for the fields of physical remote sensing and near-interface fluid mechanics.
 
For a continuation of methods/conclusions, read the full AMS publication here.