Drop characteristics from the UNIGE calibration device for non-catching precipitation instruments

These data are from the paper "Calibration uncertainty of non-catching precipitation gauges", by Baire, Q. et al., accepted for publication on the journal Sensors. A rain drop generator, developed at the University of Genova, is presented in that paper using two high-precision syringe pumps, with a capacity of 20 and 1 ml (20 and 4.5 mm piston diameter, respectively), to produce water drops of the required volume. An electric field, generated by a high voltage trigger, allows releasing each single drop on demand. Each drop is generated at the tip of a suitable nozzle by dispensing the necessary volume to achieve the desired drop size and then detached by exploiting a 5 kV potential difference, where the water is negatively charged and attracted by a metal ring (positively charged), positioned just below the tip of the nozzle. By using different nozzles/needles and the proper syringe pump, drops of various size are produced.

Validation of drop size measurements was obtained by weighing the total volume of samples of about 20 to 45 drops with a precision balance having a resolution of 0.001 g. Drops were released at 1.20 m above the center of the measurement plane of the camera.

Results are summarized in Table 2 in the paper in terms of the average drop diameter obtained from the software and the balance, and their difference. Drop size characteristics as obtained from the photogrammetric system are included in the database for the generated sets of drops. A second set of tests was conducted using the photogrammetric system alone, without weighing the overall water volume. Statistics of the detected drop diameter and fall velocity are listed in Tables 3 and 4 in the paper, together with the number of released drops during each test, while the single drop size and fall velocity characteristics are included in the dataset.