Modeling the Spatial Response of the Airfoil Shear Probe Using Different Sized Probes

Abstract

The airfoil shear probe is the only robust sensor currently available for measuring the rate of dissipation of kinetic energy in the ocean. The wavenumber (or spatial) resolution of the shear probe is determined by its physical dimensions, while the bandwidth of shear fluctuations is determined by the rate of dissipation. For most oceanic work, the conventional airfoil probe resolves the shear spectrum adequately. However, measurements taken in regions of larger dissipation rates, such as boundary layers, require a resolution beyond that of currently available shear probes. A newly designed probe, with dimensions approximately one-half of those of the conventional probe, was tested side by side with the conventional probe in a vigorously turbulent tidal channel. The relative response of the two types of probes indicates that both probes are characterized by a single-pole low-pass filter, with half-power wavenumbers of 49 and 88 cpm for the larger and smaller probes, respectively. After correction for this response, the spectra from both probes agree closely for the dissipation range 10?7 to 10?4 W kg?1. Variance estimates from corrected spectra only agree with the Nasmyth empirical spectrum over a limited range in dissipation rate.