Toru Shiina

Z-R relation for snowfall using two small doppler radars and snow particle images

Snowfall data was simultaneously recorded by two small Doppler radars, two high sensitive snow gages and an image processing system with high accuracy at short time interval. The snowfall rate R was measured with two gauges and radar reflectivity factor Z was measured using small bistatic X-band radar and monostatic K-band radar. The images of falling snow particles were used to obtain size distribution. Since all the measurements were located in a small area, it can be said that the obtained data corresponds well to others, and it is possible to analyze Z-R relation in detail. The relationships between two radar reflectivity factors and snowfall rate were investigated and compared to the characteristics of snow particles.

Image processing of snow particles and classification into snowflakes and graupel

To analyze the relationship between the radar reflectivity and the intensity of a snowfall, it is important to know the percentages of snowflakes and graupel in snow particles. This paper proposes an automatic method of classification of falling snow particles. The method consists of two CCD cameras which record each particle simultaneously with different shutter speeds and magnifications. The first CCD camera has a slow shutter speed (1/60 s) and a relatively wide view angle, and records the trailing image and diameter of each falling snow particle so that its fall velocity is obtained, and this camera also records the distribution of diameters of the snow particles. The second CCD camera has a higher shutter speed (1/8000 s) and a narrow view field (1/5 the first CCD camera), and records a binary image and a gray-level image of each snow particle so that the shape parameter of each particle can be obtained. Each snow particle is classified as a snowflake or a graupel pellet by image processing based on the fall velocity and shape parameter. The proposed method has been successfully tested in snowfall (continuously for 2 weeks), obtaining the percentages of snowflakes and graupel once a minute in real time.

Snow particle extraction and analysis using the differential of sequential images

In this study, we have discussed improvement of the image processing for the snowfall measurement. Presenting improvement is the snowfall extraction from backgrounds. This extraction is executed using the luminescence Y and the luminescence differential D from the image. The extraction operates stable with two comparison process Y against ThLUM and D against ThDIFF . The snowfall extraction presented in this study has advantage to general motion sampling in its analysis speed. Attaching this extraction to the former snow analysis, we can apply images containing various backgrounds to the analysis.

Measurement of Z-R relations using a small Doppler radar and image data of snow particles

Presents a new system to measure physical snowfall parameters using image processing techniques. It is possible to calculate the snowfall rate from the mass and volume of each snow particle. Using image data, it is also possible to calculate the radar reflectivity Z, assuming Rayleigh scattering and discrete data. The relationship between X-band wave attenuation, Z and snowfall rate was investigated and compared to the characteristics of snow particles. It was suggested that the power spectrum is related with the content of ice crystals.