Abstract: A coherent laser radar or lidar device (2;20;84;90) for measuring wind speed is described that comprises a transmitter for transmitting a beam of light to a remote probe volume (6;54), a receiver for detecting back-scattered light and an analyser for calculating wind velocity at the remote probe volume from the Doppler shift in frequency of the detected back-scattered light. The analyser is arranged to monitor for the presence of, and/or to ensure the calculated wind speed is corrected for, any Doppler frequency components of the detected back-scattered light that arise from back-scatter off cloud located at a range greater than the range of the remote probe volume. It is described how the lidar (2;20;84;90) may be scanned and wind velocity components calculated by fitting the scanned line of sight velocity values to a predetermined function. Furthermore, it is outlined how an initial fit may be performed to determine which points are to be used in this calculation.