Dynamic response of thin-wire wave gauges

A series of experiments was conducted in a wind-wave tank to determine the dynamic response of thin-wire wave gauges as a function of probe diameter in terms of their spatial resolution and frequency response. Two resistance thin-wire gauges with probe diameters of 0.13 and 0.4 mm were used in the experiments. They were calibrated against a nonintrusive, optical device (the laser displacement gauge, or LDG). The two thin wires were mounted side by side in close proximity to the laser beam at a fetch of 4 m. The outputs from the LDG and thin-wire gauges were recorded alternately as well as simultaneously by using two separate recording systems. The spectral density measured with the LDG proves to be consistently higher than that measured with either thin wire, especially for frequencies higher than the dominant frequency. Only a slight difference is observed between the two spectra of the thin-wire data. From the experimental results, an empirical correction for the meniscus-induced bias in the variance spectrum of capillary waves is derived.