Remote measurement of turbulent wind spectra by heterodyne Doppler lidar technique

Heterodyne Doppler lidars (HDLs) are used to monitor atmospheric wind field and wind turbulence at remote distance. This last application calls for th e derivation of wind spectra, which can be characterized by the dissipation rate and the kappa -spectral peak (or outer scale of turbulence). However, the HDL technique may suffer two problems. First, HDL measurements result in spatial averaging of the true wind velocity along the line of sight, bec ause of the laser pulse duration and windowing effect on processed signals. Second, even at high signal-to-noise ratio, the retrieved turbulent veloci ty field may be contaminated by errors due to speckle fluctuations. It is s hown that both spatial averaging and error contribution to the wind spectra can be modeled starting from the transmitted laser pulse characteristics a nd signal processing parameters, so that their effect can be predicted. The rms difference between the estimated and predicted turbulent spectra is mi nimized in order to infer the turbulence parameters. This procedure is test ed on simulated signals and validated on actual data taken by a 10-mum HDL during a field campaign in 1995. The data collected during two periods of two consecutive days (9 and 10 Mar ch and 13 and 14 March 1995) are analyzed. On these days, moderate to light winds prevailed. The stability parameter z(i)/L-MO indicated slightly unst able conditions with sometimes probable convection. The HDL measured energy dissipation rates ranging between 0.7 x 10(-3) and 8 x 10(-3) m(2) s(-3) i n good agreement with sonic anemometer measurements. The kappa -spectral pe ak ranged between 200 and 600 m.