Effects of Wind Turbulence on Coherent Doppler Lidar Performance

Abstract

The effects of wind turbulence on pulsed coherent Doppler lidar performance are investigated theoretically and with computer simulations. The performance of velocity estimators is determined for the case of a single realization of a wind field described by a Kolmogorov spatial spectrum and for an ensemble average over many realizations. The results are compared with previously published data. The important normalized physical parameters are identified to reduce the parameter space. For a given realization of a random wind field, the mean Doppler lidar velocity (an ensemble average over the random aerosol particles) is a function of the lidar parameters and the instantaneous radial velocity over the sensing volume of the lidar pulse. Various approximations for the mean Doppler lidar velocity are compared using computer simulations. The best approximation for the mean Doppler lidar velocity is used to calculate the effects of the spatial averaging of the radial velocity by the lidar pulse on Doppler lidar estimates of the spatial structure function of the velocity and the variance of the velocity. Doppler lidar estimates of point statistics of the wind field (velocity variance, spatial velocity structure function, energy dissipation rate) are possible for certain conditions. Using numerical simulations, the statistical description of common velocity estimators is determined by performing the ensemble average over many realizations of a stationary wind field. Velocity estimator error extracted from 2-?m coherent Doppler lidar data in the surface layer are shown to be within 5% of simulation results that include the effects of wind turbulence. For typical surface-layer measurements, a linear array of in situ wind sensors along the lidar propagation direction would be required to produce reliable comparison of in situ measurement with coherent Doppler lidar wind measurements. The effects of wind turbulence on the performance of 2- and 10-?m coherent Doppler lidars for space-based operation are also presented.