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Open AccessArticle

Uncertainty in Measured Raindrop Size Distributions from Four Types of Collocated Instruments

1
Department of Atmospheric Sciences, National Central University, Taoyuan 32001, Taiwan
2
Department of Astronomy and Atmospheric Sciences, Center for Atmospheric Remote sensing (CARE), Kyungpook National University, Daegu 41566, Korea
3
Department of Atmospheric Sciences, National Taiwan University, Taipei 10617, Taiwan
4
National Center for Atmospheric Research, Boulder, CO 80301, USA
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(7), 1167; https://doi.org/10.3390/rs12071167
Received: 20 February 2020 / Revised: 27 March 2020 / Accepted: 1 April 2020 / Published: 5 April 2020
(This article belongs to the Special Issue Precipitation and Water Cycle Measurements Using Remote Sensing)
Four types (2D-video disdrometer: 2DVD; precipitation occurrence sensor system: POSS; micro-rain radar: MRR; and Joss–Waldvogel disdrometer: JWD) of sixteen instruments were collocated within a square area of 400 m2 from 16 April to 8 May 2008 for intercomparison of drop size distribution (DSD) of rain. This unique dataset was used to study the inherent measurement uncertainty due to the diversity of the measuring principles and sampling sizes of the four types of instruments. The DSD intercomparison shows generally good agreement among them, except that the POSS and MRR had higher concentrations of small raindrops (<1.0 mm) and offered a better chance to observe big raindrops (>5.2 mm). The measurement uncertainty ( σ ) was obtained quantitatively after considering the zero or non-zero measurement error covariance between two instruments of the same type. The results indicate the measurement uncertainties were found to be neither independent nor identical among the same type of instruments. The MRR is relatively accurate (lower σ ) due to large sampling volumes and accurate measurement of the Doppler power spectrum. The JWD is the least accurate due to the small sampling volumes. The σ decreases rapidly with increasing time-averaging window. The 2DVD shows the best accuracy of R in longer averaging time, but this is not true for Z due to the small sampling volume. The MRR outperformed other instruments for Z for entire averaging time due to its measuring principle. View Full-Text
Keywords: drop size distribution; uncertainty; sampling volume; disdrometer; measuring principle drop size distribution; uncertainty; sampling volume; disdrometer; measuring principle
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MDPI and ACS Style

Chang, W.-Y.; Lee, G.; Jou, B. .-D.; Lee, W.-C.; Lin, P.-L.; Yu, C.-K. Uncertainty in Measured Raindrop Size Distributions from Four Types of Collocated Instruments. Remote Sens. 2020, 12, 1167.

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