Method for measuring microphysical characteristics of natural precipitation using particle image velocimetry

摘要

A method and video sensor for precipitation microphysical features measurement based on particle image velocimetry. The CCD camera is placed facing towards the light source, which forms a three-dimensional sampling space. As the precipitation particles fall through the sampling space, double-exposure images of precipitation particles illuminated by pulse light source are recorded by CCD camera. Combined with the telecentric imaging system, the time between the two exposures are adaptive and can be adjusted according to the velocity of precipitation particles. The size and shape can be obtained by the images of particles; the fall velocity can be calculated by particle displacement in the double-exposure image and interval time; the drop size distribution and velocity distribution, precipitation intensity, and accumulated precipitation amount can be calculated by time integration. This invention provides a method for measuring the shape, size, velocity, and other microphysical characteristics of various precipitation particles.

主权项

1. A method for measuring microphysical characteristics of precipitation particles using particle image velocimetry comprising following steps:
a. a CCD camera is placed facing towards the light source, which forms a three-dimensional sampling space; b. auto-correlation images of precipitation particles illuminated by pulse light source are recorded by CCD camera; c. horizontal and vertical dimensions of particles are inferred from the images based on the scaling relation between the images and the size; d. shape, axis ratio, as well as orientation of particles are calculated by the image processing algorithm; e. vertical and horizontal velocities of particles are calculated according to the particle displacement in double-exposure image and interval time; f. phases of precipitation particles are classified according to the shape of particles, and the relationship between the velocity and size of particles; wherein the defocused and noisy images are restored using the median filtering and point spread function, the shape, size, axis ratio, orientation of particles are calculated based on grayscale and contour of images, and the fall velocity of particles are calculated from auto-correlation images using the particle grayscale tracking method.