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. The Laser Disdrometer VAP for Quality-Controlled Measurements, using PyDSD (LDQUANTS) uses standard methods from Tokay et al. (e.g., 2013; 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.