Frequency response of hot wires used for atmospheric turbulence measurements in the marine environment

We have examined the frequency response of hot wire anemometers using 4.5-μ tungsten wires with laboratory-produced salt layers. The salt layers are produced by exposure of the heated wire to a NaCl–water aerosol and are intended to simulate salt layers produced on wires used in the marine environment. The frequency dependence was determined by measuring the response of the wires to a sinusoidal velocity field generated in a sound chamber. The relaxation frequency (or rolloff frequency) was found to vary as t−2, where t is the thickness of the salt layer, in agreement with the theory presented in this paper. In addition, the dc calibration parameters for thick coatings were investigated and compared with theory.