Laser Profiling of Wind and Turbulence

We present a novel approach for laser profiling of wind and turbulence in the atmospheric boundary layer. By transmitting a train of laser pulses and measuring their backscattered intensity fluctuations, resulting from aerosol density variations, we were able to determine the wind velocity and turbulence strength prevailing in the scattering volume. The received pulses were imaged onto three fast detectors and their spatial-temporal cross-correlation function was calculated, allowing for determination of the wind vector and turbulence strength of the measured volume. Time of flight technique, together with laser pulses in the tens of nanoseconds range provided a ~20m slice for profiling purposes. This concept was demonstrated using a coaxial transmitter/ receiver configuration. A 0.5 mJ/ 20 kHz fiber laser was used for transmission, while a 15cm Cassegrain telescope with three avalanche photo-diodes was used for detection. Experimental results are presented and discussed in view of key method parameters: the role of local (at the scattering layer level ) fluctuations vs. path integral induced fluctuations, spot size and its dependence on layer height and on turbulence scale size, fluctuation spectrum dependence on wind and turbulence , etc. Our approach provides valuable advantages compared with the available Doppler wind profiling technology, such as: direct measurement of the transverse wind component (without scanning or multi laser beams), true local measurement which is insensitive to the topography of the area (especially in non-homogenous terrain), high output rate, direct turbulence measurement and low system cost. Typical applications are in the field of meteorology, wind farm prospecting and wind power control and optimization.