JE-YUAN HSU2025-01-032025-01-032024-03-0107390572https://www.scopus.com/record/display.uri?eid=2-s2.0-85192080482&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/724526A new rotating axes method (RAM) is developed to improve the vertical resolution of the horizontal current velocity measurements u at EM-APEX floats. Unlike the traditional harmonic fitting method (HFM), which yields u averaged in 50-s intervals, RAM decodes and interprets 1-Hz measurements of horizontal seawater velocity ũ, and averages ũ in 12-s windows for removing wind waves with a typical peak frequency; 0.12 Hz. Estimates of u from RAM agree with those from HFM but with a higher vertical resolution of;1.5 m, 4 times better than HFM. Note that extracting float signals due to seawater motion needs to assume slow-varying voltage offset DFoffset. The typical variations of estimated DFoffset do not affect the results of u significantly. Estimates of u are excluded when DFoffset fluctuates strongly in time and scatter significantly. RAM is applied to float measurements taken near Mien-Hua Canyon, Taiwan. Composite vertical shear spectra C computed using u from RAM exhibit a spectral slope of 21, as expected for the saturated internal waves in the vertical fine-scale range. The RAM provides EM-APEX float’s horizontal velocity measurements into fine vertical scales and will help improve our understanding of energy cascade from internal wave breaking and shear instability into turbulence mixing.falseAlgorithmsIn situ oceanic observationsMeasurementsMixingOceanic profilersjournal article2-s2.0-851920804822-s2.0-85192080482