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Impacts of Raindrop Velocity Measurement Error on Raindrop Size Distribution Estimation from PARSIVEL Disdrometer
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摘要: 该文研究PARSIVEL激光雨滴谱仪的测量误差并提出订正方法。对2014年在广东阳江的PARSIVEL激光雨滴谱仪采集的两次降水过程数据进行分析发现，雨滴下落速度V随粒径D变化与静止大气中雨滴下落末速度随粒径变化的Atlas-Ulbrich曲线分布趋势一致，但D < 1 mm及D > 3 mm的速度偏差较大。其主要原因是大粒径雨滴形变造成速度偏离较大，仪器测量误差造成小粒径测速偏大，激光雨滴谱仪所在高度的大气垂直运动影响雨滴下落速度。根据PARSIVEL激光雨滴谱仪测量原理，基于雨滴形变与粒径关系，给出形变订正后的Atlas-Ulbrich修正曲线，并用于对小粒径测速订正。比较订正前后的雨滴谱分布，订正后的小雨滴浓度明显增加，大雨滴浓度略有减小，订正后浓度参数和斜率参数均增加，形状参数变化不明显。
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关键词:
- 激光雨滴谱仪;
- 测量误差;
- Atlas-Ulbrich修正曲线;
- 雨滴谱分布
Abstract: The error of raindrop size distribution estimation using PARSIVEL disdrometer is carefully studied, and an error correction method is proposed. Raindrop distribution data of two kind of precipitation by PARSIVEL disdrometer at Yangjiang in 2014 are analyzed. Results show that, the measured raindrop size distribution data are in good consistency with the empirical curve from Atlas, but the velocity measurement error is large when the particle size is below 1 mm or above 3 mm. The error analysis indicates that velocity measurement error of big particle is caused by deformation, while the error of small particle is caused by the instrument itself, and the vertical air motion near the disdrometer is influential for both situations.According to the detective principle of PARSIVEL disdrometor and the relationship between the deformation particle, a corrected Atlas-Ulbrich curve is given. The detective data of stratiform cloud precipitation are stable. An correction error curve of small particles is given by calculating the vertical air velocity of no less than 1 mm in diameter data from the stable precipitation, excluding the air motion in the diameter less than 1 mm. Small particle data are corrected, and the corrected raindrop distribution data are in good consistency with corrected Atlas-Ulbrich curve. The droplet concentration increases significantly and large drops concentration reduce slightly after correction. The intercept, slope and shape parameters of Gamma distribution of two kinds of precipitations are calculated before and after the correction, and the comparison shows that the corrected intercept parameter and slope parameter increase obviously, while the shape parameter barely changes. -
图 1 2014年5月8日C-FMCW雷达探测层状降水云时序图与地面雨滴分布
(a) 回波强度，(b) 径向速度，(c) 地面雨滴分布及Atlas-Ulbrich曲线
Fig. 1 Stratiform cloud evolution sequence diagram and raindrop distribution by C-FMCW on 8 May 2014
(a) reflectivity, (b) radial velocity, (c) raindrop distribution and Atlas-Ulbrich curve
图 2 2014年5月10日C-FMCW雷达探测对流云降水时序图与地面雨滴分布
(a) 回波强度，(b) 径向速度，(c) 地面雨滴分布及Atlas-Ulbrich曲线
Fig. 2 Convective cloud evolution sequence diagram and raindrop distribution by C-FMCW on 10 May 2014
(a) reflectivity, (b) radial velocity, (c) raindrop distribution and Atlas-Ulbrich curve
图 3 PARSIVEL测得的雨滴分布和Vb-Da修正曲线
(a) 层状云降水，(b) 对流云降水
Fig. 3 Raindrop data distribution after curve revised
(a) the stratiform precipitation, (b) the convective precipitation
图 4 2014年5月8日层状云降水近地面 (1.4 m) 大气平均垂直运动速度
Fig. 4 The average vertical velocity of air motion near the ground (1.4 m) at stratiform precipitation on 8 May 2014
图 5 小粒径测速误差分布订正曲线
(a) 大气垂直运动速度订正后小粒径雨滴分布与Vb-Da曲线，(b) 平均测速误差ΔV随粒径分布
Fig. 5 Velocity error distribution of small particle
(a) small particle distribution and Vb-Da curve, (b) velocity error distribution
图 6 测速修正后的雨滴分布和Vb-Da曲线
(a) 层状云，(b) 对流云
Fig. 6 Velocity revised of small particle and Vb-Da curve
(a) the stratiform precipitation, (b) the convective precipitation
图 7 对流云降水0.937 mm粒子数 (a) 和1.375 mm粒子数 (b) 与近地面大气平均垂直速度关系
Fig. 7 Relatioships between the number of 0.937 mm particles (a), the number of 1.375 mm particles (b) of convective precipitation and the average vertical velocity of the air motion near the ground
表 1 层状云降水Gamma函数3个参数订正前后比较
Table 1 Three parameters of the Gamma distribution before and after correction of the stratiform precipitation
时间 订正前 订正后 N0/(m-3·mm-1-μ) μ Λ/mm-1 N0/(m-3·mm-1-μ) μ Λ/mm-1 20:18-20:29 1.98×104 3.98 5.07 2.58×104 3.71 5.19 20:30-20:41 3.55×104 3.51 5.40 4.48×104 3.20 5.50 
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表 2 对流云降水Gamma函数3个参数订正前后比较
Table 2 Three parameters of the Gamma distribution before and after correction of the convective precipitation
时间 订正前 订正后 N0/(m-3·mm-1-μ) μ Λ/mm-1 N0/(m-3·mm-1-μ) μ Λ/mm-1 19:00-19:14 1.20×103 -0.25 1.41 1.70×103 -0.07 1.63 19:15-19:29 1.59×103 0.21 1.34 2.22×103 0.27 1.52 19:30-19:44 2.08×103 0.54 1.51 2.94×103 0.73 1.73 19:45-19:59 2.22×103 0.06 1.34 3.08×103 0.15 1.52
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