Expendable microSWIFT buoys have been developed and tested for measuring ocean surface waves. Wave spectra are calculated via onboard processing of GPS velocities sampled at 5 Hz, and wave spectra are delivered to a shore-side server via Iridium modem once per hour. The microSWIFTs support additional sensor payloads, in particular seawater conductivity and temperature. The buoys have a non-traditional, cylindrical shape that is required for deployment via the dropsonde tube of research aircraft. Multiple versions have been developed and tested, with design considerations that include: buoy hydrodynamics, sensor noise, algorithm tuning, processor power, and ease of deployment. Field testing in a range of conditions, including near sea ice and in a hurricane, has validated the design.

The Surface Wave Instrument Float with Tracking (SWIFT) is a freely drifting platform for measurements of waves, currents, and turbulence in the ocean surface layer. This platform has been used globally to study wave breaking, wave-current interactions, and waves in ice. A new version (v4) of the buoy has recently been developed and demonstrated in the Office of Naval Research "Langmuir Circulations" field campaign along the California coast (2017). The new version is built around a 5-beam Acoustic Doppler Current Profiler (Nortek Signature 1000) with a multi-pulse coherent mode for high-resolution turbulence measurements. The new Doppler profiler enables estimates of the turbulent dissipation rate down to 3.5 m below waves, compared with 0.5 m in the previous version, and can measure a much larger range of turbulence levels than the previous version. The new version also uses a broadband Doppler mode to profile the mean currents down to 20 m. Mean Eulerian velocity profiles are estimated from the wave-averaged profiler velocities by applying a wave-following bias correction that scales with the Stokes drift and has twice the vertical decay scale. Finally, the new version supports real-time telemetry of raw sea surface elevations for reconstruction of individual waves by processing a coherent array of multiple SWIFTs, with applications for short-range wave-by-wave forecasting. These combined improvements to the platform are intended to advance understanding of wave processes and applications in the ocean surface layer.

This work details a methodology for measuring hub height inflow turbulence using moored acoustic Doppler velocimiters (ADVs). This approach is motivated by the shortcomings of alternatives. For example, remote velocity measurements (i.e., from acoustic Doppler profilers) lack sufficient precision for device simulation, and rigid tower-mounted measurements are very expensive and technically challenging in the tidal environment. Moorings offer a low-cost, site-adaptable and robust deployment platform, and ADVs provide the necessary precision to accurately quantify turbulence.

The effects of biofouling on a wave measurement buoy are examined using concurrent data collected with two Datawell Waveriders at Ocean Station P: one heavily biofouled at the end of a 26-month deployment, the other newly deployed and clean. The effects are limited to the high-frequency response of the buoy and are correctly diagnosed with the spectral "check factors" that compare horizontal and vertical displacements. A simple prediction for the progressive change in frequency response during biofouling reproduces the check factors over time. The bulk statistical parameters of significant wave height, peak period, average period, and peak direction are only slightly affected by the biofouling because the contaminated frequencies have very low energy throughout the comparison dataset.

Two recent methods for making high-fidelity turbulence measurements from moving platforms are described and demonstrated. The first is a method for measuring profiles of near-surface turbulence from a wave-following 'SWIFT' buoy. The second is a method for measuring time series of turbulence from a submerged compliant mooring. Both approaches use coherent Doppler instruments and inertial motion units (IMUs). In the buoy method, wave motions (e.g., pitch, roll, and heave) are quantified via GPS and IMU measurements. These wave motions are not present in the turbulence observations, because buoy follows the wave orbital motion, and thus the turbulent velocities are processed in the wave-following reference frame. In the mooring method, IMU measurements track the mooring motions (e.g., strum and kiting) and these motions are removed in post-processing to obtain turbulent velocities in the fixed earth reference frame. These approaches successfully quantify turbulence in regions previously unavailable or limited by the noise and spatial aliasing of sampling from bottom-mounted platforms.

A compliant mooring to collect high frequency turbulence data at a tidal energy site is evaluated in a series of short demonstration deployments. The Tidal Turbulence Mooring (TTM) improves upon recent bottom-mounted approaches by suspending Acoustic Doppler Velocimeters (ADVs) at mid-water depths (which are more relevant to tidal turbines). The ADV turbulence data are superior to Acoustic Doppler Current Profiler (ADCP) data, but are subject to motion contamination when suspended on a mooring in strong currents. In this demonstration, passive stabilization is shown to be sufficient for acquiring bulk statistics of the turbulence, without motion correction. With motion correction (post-processing), data quality is further improved. Results from two field sites are compared, and the differences are attributed to the generation of large eddies by headlands and sills.