Sampling variability effects in drop‐resolving disdrometer observations

Abstract

Rain events are often studied with raindrop disdrometers—instruments designed to measure and record individual drop properties. Data from these instruments reveal that the instantaneous raindrop arrival rate is highly variable, with drop counts in consecutive time intervals occasionally changing by an order of magnitude or more. These drop count fluctuations result from some unknown combination of real physical changes in the underlying rainfall in conjunction with statistical fluctuations due to instrumental imperfections, limited sampling area, and the correlated nature of drop arrivals. Here empirical observations are used to drive a simulation that explores the degree to which observed variability in bulk rainfall observations might be produced by statistical fluctuations. It is shown that meaningful conclusions about true underlying rain properties require more drops than previously thought. Revisions to the interpretation of disdrometer data are discussed.

Rainfall intensity in geomorphology: Challenges and opportunities

“…This specifies the number of droplet impacts per unit area and unit time. Large droplet impacts are generally less frequent than small droplet impacts, according to the size distribution of drops, in turn related to the rainfall intensity (Larsen and O’Dell, 2016).…”

Identification and Characterization of an Anomaly in Two-Dimensional Video Disdrometer Data

“…Although data from six different 2DVDs were used above to demonstrate the ubiquity of this anomaly, the majority of the data utilized was gathered by 2DVD SN074 which has been running mostly continuously in a single location near Hollywood, South Carolina since December 2013. This particular 2DVD is known to have been maintained following manufacturer recommendations by the authors and its performance has been frequently validated by reasonable agreement with a large number of other disdrometric instruments nearby, including (for part of the time) another 2DVD (SN098) located about 250 m away [17,23,25]. The detailed characterization that follows is based on the 252 events measured by 2DVD SN074.…”

Refinements to Data Acquired by 2-Dimensional Video Disdrometers

“…The regular recommended maintenance has been performed to periodically recalibrate/measure the vertical distance between the horizontal light sheets and recalibrate the internal sizing algorithm. The instruments have been validated against each other and against measurements taken with an array of Thies Clima Laser Precipitation Monitors [24,30,33,42,68]. Additionally, a previous study took an in-depth look at the data from these sensors and four other 2DVDs and did not reveal any notable discrepancies in the general structure of the data [42].…”