Showing papers on "Disdrometer published in 1987"
TL;DR: In this paper, a shadowgraph-type imaging system was used to measure the size and concentration of raindrops in a cylindrical sample volume, where each drop produces two equally sized pulses, the heights of which are proportional to the drop's diameter and their separation yields the transit time.
Abstract: An instrument for measuring the size and concentration of raindrops is described which has the ability to function equally well in calm conditions and strong winds. Raindrops are detected optically in a shadowgraph-type imaging system. A unique feature of the device is the sensing of drop size as drops enter and leave a cylindrical sample volume. Each drop produces two equally sized pulses, the heights of which are proportional to the drop's diameter and their separation yields the drop's transit time. The drop concentration can be derived from this data without assuming or measuring drop velocities. The instrument has a large sample volume, but a negligible loss of data resulting from two drops being sampled simultaneously. Drops above 300 μm can be detected, but beam divergence limits accurate sizing to drops larger than 400 μm. Laboratory calibration shows that drops greater than 1 mm in diameter may be sized to better than 5%. Comparison tests with a tipping bucket raingage reveal that time i...
50 citations
TL;DR: In this paper, the authors compared the performance of dual-polarization radar measurements with ground-based disdrometer measurements located 47.1 km away from the radar.
Abstract: Rainfall parameters estimated from dual-polarization radar measurements using the differential-reflectivity technique are compared with ground-based disdrometer measurements located 47.1 km from the radar. This case study is based on data obtained during an experiment in central Illinois on October 29, 1982. Both empirical and model relationships between radar observables and rainfall parameters ters are tested. The differential-reflectivity technique is compared with the conventional Z -R technique and is shown to provide improvements in the estimation of rainfall rate by radar. The analysis includes careful consideration of the spatial and temporal factors relating the radar-scattering volumes to the location and duration of ground-based disdrometer measurements. The significance of these factors (mainly due to the horizontal and vertical motion of raindrops) in radar-disdrometer comparisons is evident in the results.
30 citations
TL;DR: In this article, empirical power law relations of the form Y = aRb have been obtained between the rainfall rate R, the radar reflectivity factor Z, liquid water content M, optical extinction σ and the median volume diameter D0 for three types of rainfall.
Abstract: The rain dropsize distributions measured by a disdrometer in 21 rain events consisting of 1, 640one-minute dropsize spectra have been analyzed for a tropical station, Ile-Ife (geog. lat. 7.5°N, long 4.5°E) in South-Western Nigeria. Empirical power law relations of the form Y = aRb have been obtained between the rainfall rate R, the radar reflectivity factor Z, liquid water content M, optical extinction σ and the median volume diameter D0 for three types of rainfall. A power law relationship was also obtained between the median volume diameter D0 and the liquid water content M. The variability in a and b with rain parameters, rain events and rain types is discussed. The empirical relations have been compared with existing relations for other parts of the world, for their utilization in radar meteorology and radar engineering.
14 citations
TL;DR: In this article, preliminary data from ground-based measurements of rainfall using an optical disdrometer and high-resolution rain gage network is described, and the recurrence of the rain period is shown to be non-Poisson with evidence of clustering.
Abstract: Preliminary data from ground-based measurements of rainfall using an optical disdrometer and high-resolution rain gage network are described. The recurrence of the rain period is shown to be non-Poisson with evidence of clustering, whereas a lognormal distribution is shown to be an approximate fit to the distribution of amount of rainfall in a rain period. About 40% of rain periods possess a total rainfall smaller than that resolvable by conventional recording rain gages; three-quarters of these were resolvable by the high-resolution rain gages used. Rapid fluctuations of rainfall intensity (∼1 mm h−1 s−1) are evident in individual rainfall intensity records and the distribution of duration of rainfall above a specified threshold intensity is shown to be approximately lognormal; these observations are consistent with a lognormal distribution of precipitation region sizes. An empirical fit to the average fractional duration of rainfall is given, although the curve is generally a poor fit to fracti...
11 citations
TL;DR: In this paper, a data-acquisition and real-time processing system designed for disdrometer measurements is presented based on a portable microcomputer which acquires and processes the data, records the size distribution every minute, and displays and prints the distributions and selected integrated parameters of the precipitation.
Abstract: The disdrometer is an instrument used worldwide to measure the size distribution of raindrops at ground level. In this paper, a data-acquisition and real-time processing system designed for disdrometer measurements is presented. It is based on a portable microcomputer which acquires and processes the data, records the size distribution every minute, and displays and prints the distributions and selected integrated parameters of the precipitation. The last part of the paper presents examples of studies performed with the system on varied types of rainfall.
8 citations