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Microphysical properties of precipitating hydrometeors, such as size, concentration, or shape, can be retrieved by vertically-resolved remote-sensing measurements. For a thorough quality assessment, a direct evaluation of those retrievals is required. Surface in-situ observations of precipitation particles are one possible approach. In the framework of the Master’s thesis presented in here, the two-dimensional video disdrometer (2DVD), a ground-based precipitation sensor was applied for this purpose. The 2DVD provides horizontal line scans of two orthogonally aligned cameras so that hydrometeors in a well-defined measurement area are detected. This allows the derivation of single-particle properties as well as precipitation rates, particle number concentrations, or particle size distributions. In this thesis defense, the 2DVD including its measurement and calibration principle, the data processing chain, as well as former 2DVD-related research is presented. Further, the successful instrument evaluation of the 2DVD against other precipitation in-situ sensors and its capabilities to distinguish different ice crystal shapes will be elaborated on. Additionally, case studies about combined 2DVD and remote-sensing observations of cloud seeding experiments will be shown to demonstrate that the 2DVD can contribute to the investigation of clouds and precipitation processes. Data used in this thesis were collected during the PolarCAP / CLOUDLAB campaign near Eriswil, Switzerland between 12/2022 and 02/2023.:1 Introduction 2 Measurement campaign and operating instruments 2.1 Cloudlab and PolarCAP 2.2 Instrument overview 2.3 Two-dimensional video disdrometer (2DVD) 2.3.1 Measurement principle and data processing 2.3.2 Calibration procedure 2.3.3 Former 2DVD research 2.4 HOLIMO 3 2DVD – deducible hydrometeor and precipitation properties 3.1 Properties of single particles 3.2 Precipitation properties 3.2.1 Precipitation rate 3.2.2 Particle size distribution 3.2.3 Relations of particle properties 3.2.4 Particle number concentration 4 Measurement results 4.1 2DVD calibration and evaluation 4.1.1 Calibration procedure on 12 December 2022 4.1.2 Comparison of precipitation rates of different instruments 4.2 Detection of different ice crystal shapes 4.2.1 17 January 2023, 11:30 – 11:35 UTC: irregular crystals and aggregates 4.2.2 17 January 2023, 13:50 – 13:54 UTC: dendrites, strongly rimed particles, irregular crystals 4.2.3 17 January 2023, 14:07 – 14:11 UTC: dendrites 4.2.4 18 January 2023, 09:44 – 09:48 UTC: needles / columns 4.3 Case studies: Precipitation monitoring during cloud seeding experiments 5 Discussion 6 Summary, Conclusions, and Outlook Appendix A 2DVD data processing chain Appendix B Calibration offset between Mira-35 and RPG94 LACROS Appendix C Unrealistic particles not filtered by the 2DVD sno-algorithm Bibliography

Spatial distribution of precipitation in complex terrain can be very uneven and there are many factors to consider when studying it. The goal of this study was such a problem; to analyse the difference in observed annual precipitation in the complex terrain of Seyðisfjörður, a fjord in East-Iceland. The study was carried out in three parts. First, it was investigated if there was a systematic difference between measurement methods using different instruments. Second, the effect of the complex terrain on the spatial distribution of precipitation was investigated, and lastly if this observed difference could be linked to any certain kind of weather regimes. To simplify the analysis, only liquid precipitation was included in the data set.  In Seyðisfjörður there are three divergently located precipitation gauges of three different types and set up. At the Icelandic Meteorological Office in Reykjavík the same type of gauges are co-located with the exact same set up as in Seyðisfjörður. A statistical analysis of those measurements showed that there is a systematic undercatch in tipping bucket gauges compared to weighted capacity and standard accumulation gauges. However, the difference is insignificant in size compared to the observed difference in the complex terrain. The complex terrain was found to highly affect the airflow and therefore the spatial distribution of precipitation, as it almost only rains in synoptic wind directions with an easterly component (measured at a mountain station). To connect events where there was a great difference in precipitation measurements to the synoptic weather situation over the North-Atlantic, a projection connecting the geostrophic and local winds in the fjord was made. It showed that great precipitation as well as when great differences are observed, during two kind of weather regimes. One where a low pressure is travelling along the North-Atlantic storm track to the Norwegian Sea. The other were a low pressure is stationed southwest or west of Iceland in the Irminger Sea and a high pressure stretching up over Scandinavia. Convective precipitation makes up for a minimal part of the total precipitation and is not linked to events with great observed difference. Events with considerable precipitation but little observed difference are fewer and smaller than the events with much great observed precipitation and differences.