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 analyzer for calculating wind velocity at the remote probe volume from the Doppler shift in frequency of the detected back-scattered light. The analyzer 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.

Abstract: An apparatus for producing a digital depiction of a signal (10) which is adaptive to the signal itself. A constant rate sampling means, such as an analogue to digital converter (2), samples the signal (10) at a constant rate and produces a first digital depiction (12) of a signal. A transformation means (14) is responsive to the first digital depiction (12) and produces a second digital depiction based on the evolution of the signal. The transformation means may be capable of determining when a predetermined threshold level has been crossed and measuring the time interval between predetermined threshold level crossings. The transformation means (14) may include a logic arrangement and a timer counter and is run from a clock signal (16) from the same clock (6) as drives the sampling means. A method of adapting a conventional ADC (2) to adaptively sample the signal (10) by adding a transformation means (14) run off the same clock (6) as the ADC (2) is also provided.