Souki OYANAGI

Study on the Improvement of Precipitation Amount Estimation Methods by an Optical Measuring Device of Solid Precipitation Type and Precipitation Intensity

Toshiro KUMAKURA

In snowfall measurements, gauges often experience catchment losses, and devices that can identify types of precipitation tend to be costly. Kumakura et al.(2018) introduced Optical Measuring Device of Solid Precipitation Type and Precipitation Intensity(PDS), a cost-effective solution with reduced catch efficiency. Endo(2020), further examined how PDS's precipitation estimates are influenced by wind, proposing a correction formula. This solution, however, implies the need for additional wind-measuring instruments, escalating expenses. An ideal scenario would allow PDS to autonomously adjust for wind influences. Additionally, the effect of different precipitation types on measurement accuracy remains insufficiently researched.
This study seeks to mitigate these challenges by introducing a technique for deducing wind speed components exclusively using PDS, while also assessing how varying precipitation types affect measurement precision. Through controlled indoor tests employing a device that simulates two types of solid particles, we found that while the device tends to slightly undermeasure snowflake-like snowfall, it considerably overestimates sleet-like precipitation. This indicates the estimation method of pseudo fall speed across the snow types is not suitable for these tests.
To autonomously estimate wind speed components with PDS, we propose utilizing the waveform generated from changes in path length and brightness as snow particles through the PDS's irradiation zone. These waveforms help to estimate the incidence zenith angle of snow particles, which allows for the estimation of wind speed components along the PDS's optical axis combined with their fall speed. Despite challenges in standardizing precipitation particle shapes and the variation in their fall paths, our method indicates a practical approach for estimating wind effects using only the PDS. Even under indoor experimental conditions, there is variation in falling paths due to differences in the shapes of precipitation particles. Therefore, a model function created from the model was fitted to the experimental results. It is suggested from the experimental results that it is possible to estimate the incident zenith angle using the actual waveform.