Abstract
Abstract. A new method to determine the shape and fall velocity of hydrometeors by using a single CCD camera is proposed in this paper, and a prototype of a video precipitation sensor (VPS) is developed. The instrument consists of an optical unit (collimated light source with multi-mode fibre cluster), an imaging unit (planar array CCD sensor), an acquisition and control unit, and a data processing unit. The cylindrical space between the optical unit and imaging unit is sampling volume (300 mm × 40 mm × 30 mm). As the precipitation particles fall through the sampling volume, the CCD camera exposes twice in a single frame, which allows the double exposure of particles images to be obtained. 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. The innovation of VPS is that the shape, size, and velocity of precipitation particles can be measured by only one planar array CCD sensor, which can address the disadvantages of a linear scan CCD disdrometer and an impact disdrometer. Field measurements of rainfall demonstrate the VPS's capability to measure micro-physical properties of single particles and integral parameters of precipitation.
Highlights
The need for detailed knowledge on precipitation microstructure regarding precipitation remote sensing is in the following fields: terrestrial and satellite radio transmission, tropospheric wave propagation, and other atmospheric sciences and applications motivate the continuing development of various disdrometers
OTT PARSIVEL disdrometer can measure the horizontal size of particles by using a decrease of light signal by extinction; the vertical size and fall velocity of particles are estimated by the empirical assumption of raindrops’ shape (Löffler-Mang and Joss, 2000), but the difference between assumption and real rainfall can cause a distortion of raindrop size and velocity distribution
This paper presents a new ground-based video precipita- 3 tion sensor (VPS) for imaging and velocimetry of hydrometeors; it can measure the shape, size, orientation, and fall velocity of naturally falling hydrometeors simultaneously by using a planar array CCD camera with its exposure controlled precisely, which represents a promising alternative to monitor precipitation particles
Summary
The need for detailed knowledge on precipitation microstructure regarding precipitation remote sensing is in the following fields: terrestrial and satellite radio transmission, tropospheric wave propagation, and other atmospheric sciences and applications motivate the continuing development of various disdrometers. OTT PARSIVEL disdrometer can measure the horizontal size of particles by using a decrease of light signal by extinction; the vertical size and fall velocity of particles are estimated by the empirical assumption of raindrops’ shape (Löffler-Mang and Joss, 2000), but the difference between assumption and real rainfall can cause a distortion of raindrop size and velocity distribution. It cannot measure particle shape (Battaglia et al, 2010). Software running on the terminal receives the data obtained by the sensor, processes the hydrometeors’ images, and calculates the size, velocity, and shape of hydrometeors
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