The 13th Symposium on Boundary Layers and Turbulence

### P2B.24

LINEAR TIME-INVARIANT COMPENSATION OF CUP ANEMOMETER INERTIA

Tihomir Hristov, Univ. of California, Irvine, CA; and C. Friehe

We propose a method to compensate for the phase lag and the amplitude attenuation in cup anemometer signals. These two effects, caused by the instruments inertia, are the major flaws of the cup anemometer in addition to over-speeding.

Cup devices have been routinely used to obtain information about the structure and the dynamics of the atmospheric surface layer by measuring the mean wind speed profiles. The error in the averaged cup anemometer signals is introduced mostly by over-speeding, which is a nonlinear effect. In the more-recently-conducted Marine Boundary Layers (MBL) experiment one of the objectives was to understand how the structure and the dynamics of the atmospheric surface layer over the open ocean differ from these over land. Specifically, the identification of the wave-induced fluctuations of the wind speed and estimation of their amplitude and phase with respect to the underlying waves is of interest. That goal drew attention to the fact that the cup anemometers inertia was causing a phase lag and attenuation of the high frequency modes, which distorts the estimates of the quantities of interest.

Since the instrument's response is invariant in wave number (not frequency) representation, we transform the signals to be compensated from the time domain to the spatial domain by borrowing the idea from Taylor's hypothesis. The proposed procedure improves instrument performance down to spatial scales smaller than or equal to the distance constant of the anemometer

The 13th Symposium on Boundary Layers and Turbulence