RESOLVING OCEANIC SHEAR AND VELOCITY WITH THE MULTISCALE PROFILER

The Multi-Scale Profiler (MSP), a freely falling dropsonde, has been u sed over the past 12 years to measure oceanic shear variance. Complete resolution of oceanic shear spectra is achieved by combining the meas urements of MSP's acoustic current meter (ACM), electromagnetic curren t meter (ECM), and airfoil probes. The ACM detects flow relative to MS P, so the platform motion must be known to determine the water velocit y. The vehicle's tilt oscillation is inferred from accelerometer data, and its gross (point mass) horizontal motion is simulated by modeling MSP's response to the relative flow. Forcing on its rail array causes MSP to react as a point mass io fluctuations with scales as small as 2-3 m. The model of Hayes et ail for the TOPS dropsonde was modified s o that it reasonably parameterized the large MSP tail force. Relevant dynamics and data processing are discussed, and the point-mass model i s presented along with the analytic transfer functions that are used t o select parameter values, assess sensitivities, and estimate uncertai nties. Because they are unaffected bg MSP's horizontal motion, the ECM measurements directly reflect the flow structure and, consequently, p rovide an onboard reference against which the large-scale corrections to the ACM measurements are validated. Uncorrected ACM data provide a direct check on the airfoil data, which resolve microscale shear varia nce to within a factor of 2, aside from some noted exceptions in warm, turbulent waters. The motion-corrected ACM profiles are shown to reso lve shear variance to within 10%-15% at vertical scales from over 200 m down to 1 m (with minor anomalies at 5-m and 2-3-m scales).