Fast sector scan and pattern recognition for a cw laser Doppler anemometer

A fast data system was developed for a cw laser Doppler anemometer. Using a digital differentiation technique, it allows multiple peak values in a Doppler spectrum to be recorded at 50-msec intervals. Computer programs for sine wave fitting of the data for a velocity-azimuth-display (VAD) scan pattern or a reduced sector VAD scan are used to reduce the errors in the wind field determination in unfavorable weather conditions. The sector scan is necessary if the field of view is limited by buildings etc., and the time consumption for a sector scan is much less than the full VAD scan. For atmospheric inhomogeneities such as wake vortex signatures, a special pattern recognition procedure was developed. This procedure identifies inhomogeneities in the stored velocity information, and the result can be used to draw the wake vortex distribution in time or range.