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Ch Werner
and
H. Herrmann

Abstract

A description is given of a ruby lidar, differential absorption system developed for the measurement of absolute humidity profiles in the atmospheric boundary layer. Two independent temperature controlled ruby lasers are used as transmitters and the backscattered signal from each is digitized and stored separately. Prior to use, the system was calibrated over a horizontal path. Profiles of the absolute humidity have been obtained with a vertical range resolution of 100 m and these are discussed in comparison with radiosonde and airborne measurements.

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R. L. Schwiesow
,
P. Köpp
, and
Ch Werner

Abstract

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.

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F. Köpp
,
R. L. Schwiesow
, and
Ch Werner

Abstract

We have demonstrated practical measurement of profiles of horizontal wind magnitude and direction to altitudes of 750 m by making radial velocity measurements with a Doppler lidar using conical scanning. Comparison with surface anemometers and with profiles measured by balloon sondes allows one to evaluate the consistency between lidar measurements and more conventional sensors. Overall we find a correlation coefficient of 0.83 and an rms difference of 1.3 m s−1 for magnitude and a correlation coefficient of 0.91 and an rms difference of 12° for direction when the lidar and sonde profiles are compared. The differences are not a result of lidar errors because comparisons of 20 s averages between the lidar and a sonic anemometer show a correlation coefficient of 0.98, an rms difference of 0.19 m s−1, and a long-term average difference of 0.05 m s−1 for a single component. Profile differences are attributable to horizontal inhomogeneity in the wind field and uncertainty inherent in balloon sondes. Impaired visibility reduces the effective range of the lidar, and the vertical extent of the lidar sample region increases with height.s

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G. S. Kent
,
F. Köpp
, and
Ch Werner

Abstract

Remote sensing of the lower atmosphere by lidar yields profiles of the backscattering cross section along the optical path. These may be simply converted to give a qualitative picture of the distribution of atmospheric aerosol, but quantitative values can only be obtained if further information is available on aerosol properties such as refractive index and size distribution. In the experiments described below, use was made of a solar radiometer to give information on the second of these. This is then used to calculate an improved value for the ratio of backscattering to aerosol mass (β/m) for the interpretation of the lidar data. Comparison is made of the results of radiometer measurements, taken at a rural area outside Munich, with airborne lidar measurements of the tropospheric aerosol made in the same locality. Aerosol density profiles obtained in another flight made near Augsburg on 22 July 1977 show the presence of a heavy aerosol concentration over the city and the effects of the north wind are clearly visible.

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