Comparative measurement of rainfall with a precipitation micro-physical characteristics sensor, a 2D video disdrometer, an OTT PARSIVEL disdrometer, and a rain gauge

摘要

In Nanjing, China, a comparative measurement of rainfall by using a self-developed Precipitation Microphysical Characteristics Sensor (PMCS), a 2D Video Disdrometer (2DVD), a OTT PARSIVEL Disdrometer (OTT), and a tipping bucket rain gauge (Gauge) is presented to quantitatively evaluate their performances. The rain rate, rainfall duration, rainfall accumulation, raindrop size distribution (DSD), Z-R relationship, mu-lambda relationship, fall velocity, axis ratio, and their features are compared and discussed in detail. The PMCS, 2DVD, OTT and Gauge can measure the rainfall accumulation accurately, but the Gauge tends to underestimate the rainfall duration and rain rate significantly. The optical-based PMCS, 2DVD, and OTT can monitor rainfall with a higher precision in a wide range of rain rate. The PMCS, 2DVD, and OTT agree well between 0.8 and 3.25 mm. The PMCS is able to measure raindrops of at least 0.1 mm, and both the 2DVD and OTT can measure more large raindrops ( 3.5 mm). For fall velocity and axis ratio, both the PMCS and 2DVD basically agree well with the Atlas relationship, and the PMCS can describe the fall velocity with a lower deviation. It is interesting that 2.5% raindrops larger than 3 mm are found to be spherical, it may be attributed to the periodic oscillation of raindrops. This study reveals that a combination of the PMCS and 2DVD can compensate for their shortcomings and promote the DSD measurement in the entire drop size spectrum, and it's highly suggested that the reliability of DSD measurements needs careful cross-assessment after quality control.