The intensity and phase of precipitation at the ground surface can have important implications not only for meteorological and hydrological situations but also in terms of hazards and risks. In the field, Thies disdrometers are sometimes used to monitor the quantity and nature of precipitation with high temporal resolution and very low maintenance and thus provide valuable information for the management of meteorological and hydrological risks. Here, we evaluate the Thies disdrometer with respect to precipitation detection, as well as the estimation of precipitation intensity and phase at a pre-alpine site in Switzerland (1060 m a.s.l.), using a weighing precipitation gauge (OTT pluviometer) and a two-dimensional video disdrometer (2DVD) as a reference. We show that the Thies disdrometer is well suited to detect even light precipitation, reaching a hit rate of around 95 %. However, the instrument tends to systematically underestimate rainfall intensities by 16.5 %, which can be related to a systematic underestimation of the number of raindrops with diameters between 0.5 and 3.5 mm. During snowfall episodes, a similar underestimation is observed in the particle size distribution (PSD), which is, however, not reflected in intensity estimates, probably due to a compensation by snow density assumptions. To improve intensity estimates, we test PSD adjustments (to the 2DVD) and direct adjustments of the resulting intensity estimates (to the OTT pluviometer), the latter of which are able to successfully reduce the systematic deviations during rainfall in the validation period. For snowfall, the combination of the 2DVD and the OTT pluviometer seems promising as it allows for improvement of snow density estimates, which poses a challenge to all optical precipitation measurements. Finally, we show that the Thies disdrometer and the 2DVD agree well insofar as the distinction between rain and snowfall is concerned, such that an important prerequisite for the proposed correction methods is fulfilled. Uncertainties mainly persist during mixed-phase precipitation or low precipitation intensities, where the assignment of precipitation phase is technically challenging, but less relevant for practical applications. We conclude that the Thies disdrometer is suitable not only to estimate precipitation intensity but also to distinguish between rain and snowfall. The Thies disdrometer therefore seems promising for the improvement of precipitation monitoring and the nowcasting of discharge in pre-alpine areas, where considerable uncertainties with respect to these quantities are still posing a challenge to decision-making.

中文翻译：

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Thies测速仪自动进行降水监测：偏差和改进方法

地表降水的强度和阶段不仅对气象和水文状况，而且在危害和风险方面都有重要意义。在野外，蒂斯（Thies）测速仪有时用于以高时间分辨率和极低的维护量监测降水的数量和性质，从而为管理气象和水文风险提供有价值的信息。在这里，我们使用称重降水量计（OTT雨量计）和两点降水量计，评估了Thies测井仪在降水检测以及估算瑞士前高山站点（1060 m asl）的降水强度和相位方面的能力。三维视频测速仪（2DVD）作为参考。我们证明了Thies测距仪非常适合检测甚至是降水，达到约95％的命中率。但是，该仪器往往会系统性地低估降雨强度16.5％，这可能与系统性地低估了直径在0.5至3.5毫米之间的雨滴的数量有关。在降雪期间，在粒度分布（PSD）中观察到了类似的低估，但是强度估计中并未反映出这一点，这很可能是由于雪密度假设的补偿。为了提高强度估计值，我们测试了PSD调整值（针对2DVD）并直接调整了所得强度估计值（针对OTT雨量计），其中后者能够成功减少验证期间降雨期间的系统偏差。为了降雪 2DVD和OTT测斜仪的组合看起来很有希望，因为它可以改善雪密度估算，这对所有光学降水测量都构成了挑战。最后，我们证明了Thies测速仪和2DVD在降雨和降雪之间的区别方面非常吻合，从而为提出的校正方法提供了重要前提。不确定性主要在混合阶段降水或低降水强度期间持续存在，在这些阶段沉淀阶段的分配在技术上具有挑战性，但与实际应用无关。我们得出的结论是，蒂斯（Thies）测速仪不仅适合估算降水强度，还可以区分雨雪。