James Stadler Research Assistant jstadler@apl.washington.edu |
Publications |
2000-present and while at APL-UW |
![]() |
Validation of surface wave spectral measurements from velocity profiling floats Stadler, J., J. Girton, and B. Ma, "Validation of surface wave spectral measurements from velocity profiling floats," J. Atmos. Ocean. Technol., 42, 449-462, doi:10.1175/JTECH-D-24-0023.1, 2025. |
More Info |
1 May 2025 ![]() |
![]() |
|||||
EM-APEX floats have primarily been used to measure subsurface ocean velocities for the purpose of studying ocean dynamics and the vertical structure and shear of currents. However, the motionally-induced voltage sensed by the EM-APEX also contains signals from surface wave orbital velocities, and the time taken to pass through the top ~100 m of the water column is sufficient to estimate a spectrum of surface wave amplitudes with periods from 520 seconds (i.e., including both wind seas and long swell) with each profile. Following procedures developed by Hsu (2021) and D'Asaro (2015) we analyzed the performance of EM-APEX float measurements of surface-wave spectra, as well as bulk wave parameters such as significant wave height and energy period, against other in-situ wave-measuring platforms during a 2017 field study off the coast of California (ONR's Langmuir Circulation Department Research Initiative, or LC-DRI). We discuss the limitations and uncertainties inherent in the EM-APEX wave measurements, and determine the uncertainty on each individual 1Hz velocity measurement to be on the order of 1.6 cm/s, resulting in a minimal detectable significant wave height of Hs = 0.6 m. Results indicate that the EM-APEX surface wave spectral measurements are in good agreement with the other in-situ wave measurements, with correlation coefficients of R2 = 0.76 for significant wave height, and R2 = 0.65 for energy period. This work demonstrates the potential for these floats to be used as a useful tool in future direct measurements of surface-wave driven mixing processes, Langmuir turbulence, and the interactions between surface waves and ocean currents. |