Comparison of CW-Lidar-Measured Wind Values Obtained by Full Conical Scan, Conical Sector Scan and Two-Point Techniques

Continuous-wave (CW) Doppler lidar measurements of wind magnitude and direction that are based on radial velocity data on only a part of a full azimuth circle compare favorably with measurements based on a full circle. Winds were measured over an altitude range of 750 m. For example, the rms difference between 76 wind data pairs at various altitudes, taken from a full circle and from a ¼-circle sector is 0.43 m s−1 in magnitude (correlation coefficient 0.98) and 4.2° in direction, even when only 12 s of measurement time is used for the ¼-circle sector. Increased integration time leads to an even closer comparison. Useful velocity estimates can be obtained from sector scans as small as ⅙ of a circle when a weighted least-squares fitting program is used to analyze the radial velocity versus azimuth data. Results from a two-point scan technique compare less favorably with the full-scan results than do results from a sector-scan technique. A scan employing a π/2, two-point azimuth difference results in an rms difference of 0.78 m s−1 (correlation coefficient 0.95) for 2 s of measurement time when compared with a full circle scan. We conclude that even if data are available or of interest over only part of an azimuth circle, good wind estimates are still possible.