Measuring ocean waves with Saildrone uncrewed surface vehicles*

Ocean surface waves generated by hurricanes can pose a major threat to coastal life, property, marine ecosystems, and the shipping industry. Since the 2021 hurricane season, NOAA/AOML and PMEL have partnered with Saildrone Inc. to deploy 5-12 Saildrone Uncrewed Surface Vehicles (USV) every year to measure the air-sea interaction processes under hurricanes to improve hurricane forecasts. To evaluate the capability of the USV saildrones in measuring waves, this project compares wave directional spectra observed by saildrones within 10 km of moored NOAA National Data Buoy Center (NDBC) and Coastal Data Information Program (CDIP) weather/wave buoys during the 2021–2023 Atlantic hurricane seasons. Raw 20-Hz GPS and inertial measurements from saildrones were used to calculate wave information such as dominant energy spectra, wave direction, wave height, and wave period using spectral analysis techniques first developed by Longuet-Higgins et al. The introduction of updated filters and physical checks to previous methods were created to account for saildrone's non-spherical geometry. Statistical comparisons between measurements from buoys and saildrones were then used to determine the reliability of saildrone wave measurements. It was demonstrated that Saildrone Explorer USVs are capable of measuring surface ocean waves with accuracy comparable to the moored surface buoys that are specifically designed for wave measurements. Unlike moored buoys, the remotely piloted USVs can provide in situ wave measurements at global scale and target extreme conditions in remote areas. This research contributes to wind-wave and air-sea interaction research through the development of the capability of Saildrone USVs to measure ocean surface waves.