On the consistency of 2-D video disdrometers in measuring microphysical parameters of solid precipitation

[摘要] Detailed characterization and classification of precipitation is an importanttask in atmospheric research. Line scanning 2-D video disdrometer devices arewell established for rain observations. The two orthogonal views taken ofeach hydrometeor passing the sensitive area of the instrument qualify thesedevices especially for detailed characterization of nonsymmetric solidhydrometeors. However, in case of solid precipitation, problems related to thematching algorithm have to be considered and the user must be aware of thelimited spatial resolution when size and shape descriptors are analyzed.Clarifying the potential of 2-D video disdrometers in deriving size, velocityand shape parameters from single recorded pictures is the aim of this work.The need of implementing a matching algorithm suitable for mixed- and solid-phase precipitation is highlighted as an essential step in data evaluation.For this purpose simple reproducible experiments with solid steel spheres andirregularly shaped Styrofoam particles are conducted. Self-consistency ofshape parameter measurements is tested in 38 cases of real snowfall. Asa result, it was found that reliable size and shape characterization with arelative standard deviation of less than 5 % is only possible forparticles larger than 1 mm. For particles between 0.5 and 1.0 mm therelative standard deviation can grow up to 22 % for the volume, 17 %for size parameters and 14 % for shape descriptors. Testing the adaptedmatching algorithm with a reproducible experiment with Styrofoam particles, amismatch probability of less than 3 % was found. For shape parametermeasurements in case of real solid-phase precipitation, the 2-DVD showsself-consistent behavior.

[学科分类] 几何与拓扑