Diode-laser-based direct-detection Doppler wind lidar: design and initial results

Wind measurements are essential for weather forecasting and atmospheric research on all spatial and temporal scales. Despite its importance, few instruments can provide clear-air wind velocity profiles spanning both the planetary boundary layer and the free troposphere. Creating a lidar system that works in both regions is difficult, as coherent systems depend on aerosols, which are often absent in the free troposphere, while many direct-detection systems have systematic errors caused by aerosol optical properties that are not known a priori. This paper presents the initial results of a diode-laser-based direct-detection Doppler wind lidar (DWL) operating at 780 nm that uses the double-edge technique and leverages ancillary measurements of the backscatter ratio. The system uses a frequency-stabilized diode laser in a master oscillator power amplifier configuration with a tapered amplifier, producing 6.25 µJ pulses at 8 kHz (50 mW average power). Horizontal testing showed a mean bias of 0.17 m/s and a standard deviation of 1.5 m/s in the retrieved radial velocity compared to an anemometer, using bin sizes of 5 min and 37.5 m. Vertical testing demonstrated that the DWL could retrieve wind velocities with ±1σ random uncertainties of less than 3 m/s from approximately 500 m to 10.5 km at night and 500 m to at least 4.5 km during the day in clear-sky conditions, with a bin size of 15 min and 150 m. A time-varying systematic bias was also observed, changing by approximately 2 m/s over the 17 day measurement period. These results demonstrate the feasibility of the prototype DWL for measuring wind in both the planetary boundary layer and the free troposphere.