Disdrometer

About: Disdrometer is a research topic. Over the lifetime, 930 publications have been published within this topic receiving 23092 citations.

High-Frequency Single-Board Doppler Minisodar for Precipitation Measurements. Part I: Rainfall and Hail

Abstract: A high-frequency Doppler sodar for precipitation measurements has been developed. Such a Doppler sodar (6–20 kHz) can almost always measure precipitation and turbulence spectra simultaneously. Therefore, the mean vertical wind and spectral broadening effects can be directly removed. As the acoustic refractive indices for ice and liquid water are almost the same, the acoustic retrieval of precipitation can also be applied to rain with small hail (e.g., diameter D 10 mm) or large hail, but for the latter, neglecting the effects of different orientations and shapes of hailstones. The authors’ single-board minisodar is based on the digital signal processing (DSP) technique. The first prototype has been continuously operated at a coastal weather station since 25 October 2002. For stratiform rain events, the minisodar showed good agreement with a Joss–Waldvogel disdrometer and an optical rain gauge. However, for convective heavy showers, the minisodar always observed higher rain rates. The continuous, nonattended automatic operation of the minisodar has shown its capability for all kinds of precipitation measurements. The retrieval of precipitation rates for snow and graupel will be provided in a subsequent paper.

Estimation of raindrop size distribution and rain rate with infrared surveillance camera in dark conditions

Abstract: Abstract. This study estimated raindrop size distribution (DSD) and rainfall intensity with an infrared surveillance camera in dark conditions. Accordingly, rain streaks were extracted using a k-nearest-neighbor (KNN)-based algorithm. The rainfall intensity was estimated using DSD based on a physical optics analysis. The estimated DSD was verified using a disdrometer for the two rainfall events. The results are summarized as follows. First, a KNN-based algorithm can accurately recognize rain streaks from complex backgrounds captured by the camera. Second, the number concentration of raindrops obtained through closed-circuit television (CCTV) images had values between 100 and 1000 mm−1 m−3, and the root mean square error (RMSE) for the number concentration by CCTV and PARticle SIze and VELocity (PARSIVEL) was 72.3 and 131.6 mm−1 m−3 in the 0.5 to 1.5 mm section. Third, the maximum raindrop diameter and the number concentration of 1 mm or less produced similar results during the period with a high ratio of diameters of 3 mm or less. Finally, after comparing with the 15 min cumulative PARSIVEL rain rate, the mean absolute percent error (MAPE) was 49 % and 23 %, respectively. In addition, the differences according to rain rate are that the MAPE was 36 % at a rain rate of less than 2 mm h−1 and 80 % at a rate above 2 mm h−1. Also, when the rain rate was greater than 5 mm h−1, MAPE was 33 %. We confirmed the possibility of estimating an image-based DSD and rain rate obtained based on low-cost equipment during dark conditions.

Drop Size Distribution Retrievals for Light Rain and Drizzle from S-Band Polarimetric Radars

Abstract: : Measurements of full drop size distribution (DSD) spectra were used as input to scattering calculations to derive fitted equations for light rain and drizzle for estimating the mass-weighted mean diameter, D m , from radar reflectivity (Z h ) at S-band. Testing was performed using Z h measured S-band polarimetric radars over two different disdrometer locations versus D m from disdrometer measurements. Consistent results were obtained but only for Z h <18 dBZ for light rain and <5 dBZ for drizzle. Additionally, gridded radar data were used to identify light rain and drizzle regions and their D m histograms are compared with those derived from stratiform and convective rain regions.

Tracking and modeling raindrops in video sequences for assessing precipitation

Abstract: Disdrometer system is a kind of rainfall measurement tool usually developed to evaluate the raindrop size distribution and velocity of falling hydrometeors. To improve the disdrometer systems, a newly image-based technique for analyzing the raindrops was proposed in the study. This system mainly composed of three components: an optical unit with a light source; an image acquisition unit with a camera and a blackboard to grab the images; the last part is a data processing unit for estimating the collected data. To test the system, we have used glass balls and a liquid dropper to generate free-fall drops in the experiment. Subsequently, the high-speed camera captured images of the falling drops in 90 fps. Especially, the exposure time was set at 2000 ms, which resulted in the falling drops with small blurring in the assessment. We concluded that the proposed image-based disdrometer system can provide an efficient approach for the precipitation measurement by analyzing raindrop features. Moreover, this apparatus have measured micro-physical properties for quantifying the rainfall status as it only requires basic maintenance for long-lasting observation in meteorology especially in large scale areas and distributed scopes.