Atmospheric Radiation Measurement Climate Research Facility US Department of Energy

ldquants > Laser Disdrometer QuantitiesVAP Type(s) > Baseline

Disdrometers are precipitation instruments that measure drop size distributions (DSD) and associated rainfall rates/accumulation as those raindrops fall to the ground. These DSDs are a quantity of interest to modeler and observational communities. However, use of disdrometer data for model evaluation, radar monitoring, or other activities requires careful quality control and processing for key DSD properties of interest (e.g., the number concentration of drops) to ensure appropriate physical (scattering, fall speed) assumptions. LDQUANTS uses standard methods from Tokay et al. (2013 and 2014) to filter drops with unrealistic fall speeds. Further, it estimates several microphysical/geophysical quantities of parameterized DSDs (gamma or exponential assumption type fitting methods) as in following previous disdrometer studies and ARM long-term efforts.

Disdrometers are also beneficial for cross-checks with other instrumentation, including rain gauges and radars. To support research interests and related radar monitoring activities, this product calculates radar-equivalent quantities, including dual-polarization radar quantities (e.g., Reflectivity Factor Z, Differential Reflectivity ZDR), using the T-matrix scattering technique and additional wavelength, temperature, and drop shape assumptions.

All these efforts allow disdrometer data sets to become more useful and easily handled by modeling and observational studies, or routine instrumentation checks.

References: Tokay A, WA Petersen, P Gatlin, and M Wingo. 2013. “Comparison of raindrop size distribution measurements by collocated disdrometers.” Journal of Atmospheric and Oceanic Technology, 30(8), 1672–1690,

Tokay A, RJ Roche, and PG Bashor. 2014. “An experimental study of spatial variability of rainfall.” Journal of Hydrometeorology, 15(2), 801–812,


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