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Ting-I. Wang, K. B. Earnshaw, and R. S. Lawrence

Abstract

Path-averaged terminal velocity distribution of raindrops is determined from the temporal covariance function of signals from two vertically spaced linear optical detectors that respond to raindrop-induced amplitude scintillations of a projected laser beam. The known monotonic relationship between drop size and terminal velocity permits the measured velocity distribution to be converted to path-averaged drop-size distribution and, in turn, to rain rate. The large capture area of the measurements over a 200 m path allows drop-size distribution to be measured in short time intervals. We present measurements of path-averaged rain rate and raindrop size distribution made at 42 s intervals. The terminal velocity distribution during a storm that contained a mixture of rain and hail clearly shows the two-component nature of the precipitation.

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Ting-I. Wang, R. Lataitis, R. S. Lawrence, and G. R. Ochs

Abstract

Prototype Laser Weather Identifier (LWI) systems designed to detect fog, rain and snow were tested for several months at Stapleton International Airport in Denver, and at the AFGL Weather Test Facility at Otis Air Force Base, Massachusetts. We present a detailed analysis of the performance of these systems, compared with human weather observations and tipping-bucket raingages, and suggest modifications for future operational instruments.

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K. B. Earnshaw, Ting-I. Wang, R. S. Lawrence, and R. G. Greunke

Abstract

The possibility of identifying weather through the observation of forward scatter of a laser beam has been investigated. Preliminary observations with a prototype instrument suggest that it is possible to distinguish clear air, rain, snow, hail and fog using laser weather identification. After additional measurements are made in various weather conditions, it should be practical to design a simple automatic instrument to provide such information.

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Chia-Ping Cheng, Hen-I Lin, Simon Wang, Po-Ting Dean Liu, and Kung-Yueh Camyale Chao
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Mu-King Tsay, Ting-I. Wang, R. S. Lawrence, G. R. Ochs, and R. B. Fritz

Abstract

In a cooperative field study of the planetary boundary layer, three optical wind sensors were placed around a 300 m meteorological tower in a 450 m equilateral triangle 3–4 m above the terrain. It was found that the convergence measured by the three-sensor system correlates well with in situ measurements of vertical wind by anemometers located on the tower at heights up to 300 m during the occurrence of thermal plumes. By analyzing the correlation between the optically measured convergence and the vertical wind measurements made on the tower, the inversion layer, if below the top of the tower, can usually be located in the early morning when thermal plumes are active. The space-averaged horizontal wind vectors measured by the optical system have good, though not perfect, agreement with the tower measurements at the lowest layer (10 m above the ground), and with the measurements of a nearby network of surface anemometers. A comparison of the optically measured convergence with the direction of the surface horizontal wind indicates some effect of irregular terrain.

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