Abstract
Aiming at the simultaneous measurement of the size, shape, and fall velocity of precipitation particles in the natural environment, we present here a new ground-based precipitation microphysical characteristics sensor (PMCS) based on the particle imaging velocimetry technology. The PMCS can capture autocorrelated images of precipitation particles by double-exposure in one frame, by which the size, axis ratio, and fall velocity of precipitation particles can be calculated. The PMCS is calibrated by a series of glass balls with certain diameters under varying light conditions, and a self-adaptive threshold method is proposed. The shape, axis ratio, and fall velocity of raindrops were calculated and discussed based on the field measurement results of PMCS. The typical shape of large raindrop is an oblate ellipsoid, the axis ratio of raindrops decreases linearly with the diameter, the fall velocity of raindrops approaches its asymptote, and the above observed results are in good agreement with the empirical models; the synchronous observation of a PMCS, an OTT PARSIVEL disdrometer, and a rain gauge shows that the PMCS is able to measure the rain intensity, accumulated rainfall, and drop size distribution with high accuracy. These results have validated the performance of PMCS.
Highlights
The size, shape, and fall velocity of precipitation particles and their spatial distributions are important microphysical parameters playing key roles in many branches of research, such as quantitative precipitation estimation (QPE) by weather radar [1], assessment of electromagnetic wave propagation in troposphere [2], study on kinetic energy of raindrops and soil erosion [3], validation of simulated microphysics in numerical weather models [4], and parameterization of washout efficiency of particle-bound radionuclides and atmospheric pollutants in general [5, 6]
Aiming at the simultaneous measurement of the size, shape, and fall velocity of precipitation particles, we present a precipitation microphysical characteristics sensor (PMCS) based on particle image velocimetry techniques in this paper; the critical parts of PMCS are a double-pulse light source and a planar array complementary metal oxide semiconductor (CMOS) camera
In an attempt at the simultaneous measurement of the precise information of precipitation particles, a ground-based optical instrument, the precipitation microphysical characteristics sensor (PMCS) was proposed and developed, which provides a promising alternative to measuring precipitation
Summary
The size, shape, and fall velocity of precipitation particles and their spatial distributions are important microphysical parameters playing key roles in many branches of research, such as quantitative precipitation estimation (QPE) by weather radar [1], assessment of electromagnetic wave propagation in troposphere [2], study on kinetic energy of raindrops and soil erosion [3], validation of simulated microphysics in numerical weather models [4], and parameterization of washout efficiency of particle-bound radionuclides and atmospheric pollutants in general [5, 6]. The prototype of PMCS was called Video Precipitation Sensor (VPS) [11]; its performance has been validated by field experiments; the free fall of precipitation particles is affected by the instrument structure; especially in the strong wind environment, the turbulence of air flow, the splash of raindrops on the surface, and the complex variation of ambient light can induce considerable error that cannot be negligible. To address these problems, a new instrument structure which can diminish the turbulence of air flow and the splash of raindrops is designed, and an adaptive calibration method is proposed to reduce the errors of imaging. The last part summarizes the main features and future work of PMCS
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