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J. Streicher, C. Münkel, and H. Borchardt

Abstract

Each year fog at airports renders some landing operations either difficult or impossible. In such instances, visibility is the most important information for the pilot of a landing aircraft. Visibility may be constant, decreasing, or increasing with respect to the altitude; however, it is not possible to distinguish this with existing airport sensors. This paper describes a new technique for measuring slant visual range that makes use of a slant scanning device, an eye-safe laser radar.

This device has been tested by the German Meteorological Service in Quickborn, Germany, over a period of one year. A comparison with commercial visibility sensors shows that it is possible to measure visibilities with the slant-looking laser radar in the range from 50 m up to 2000 m and to even distinguish inhomogenities like ground fog. Statistics of the Quickborn measurements show that the atmosphere in that region is not homogeneous in 38% of fog situations, which would at the present lead to a restriction of the air traffic.

The first installation of this instrument at the Hamburg airport is described.

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R. K. Newsom, D. D. Turner, R. Lehtinen, C. Münkel, J. Kallio, and R. Roininen

Abstract

The performance of a novel water vapor broadband differential absorption lidar (BB-DIAL) is evaluated. This compact, eye-safe, diode-laser-based prototype was developed by Vaisala. It was designed to operate unattended in all weather conditions and to provide height-resolved measurements of water vapor mixing ratio in the lower troposphere. Evaluation of the Vaisala prototype was carried out at the U.S. Department of Energy’s Atmospheric Radiation Measurement site in north-central Oklahoma (i.e., the Southern Great Plains site) from 15 May to 12 June 2017. BB-DIAL measurements were compared with observations from radiosondes that were launched within 200 m of the BB-DIAL’s location. Radiosonde measurements are also compared with observations from a collocated Raman lidar and an Atmospheric Emitted Radiance Interferometer. During the evaluation period, the BB-DIAL operated continuously and did not experience any failures or malfunctions. The data availability was greater than 90% below 900 m but then decreased rapidly with height above this level to less than 10% above 1500 m AGL. From 106 radiosonde profiles, the overall mean difference (averaged temporally and vertically up to 1500 m) between the BB-DIAL and the radiosonde was −0.01 g kg−1, with a standard deviation of 0.65 g kg−1, and a linear correlation coefficient of 0.98. For comparison, the overall mean difference between the Raman lidar and the radiosonde was 0.07 g kg−1, with a standard deviation of 0.74 g kg−1, and a linear correlation coefficient of 0.97.

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