Disdrometer

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

Estimation of vertical profiles of raindrop size distribution from the VHF wind pro filer radar Doppler spectra

Abstract: This paper describes research on a new form of gamma drop size distribution (DSD) model that employs two arbitrary moments as free DSD parameters to enhance the flexibility in studying the characteristics of gamma DSD model to fit the spectrum. The validity of a DSD model is evaluated in terms of the stability in solving non-linear least-squares (NLLS) problem and the accuracy in DSD moment estimates. The microphysical [i.e., raindrop size distributions (DSD)] parameters are retrieved during stratiform precipitating cloud system passed (on 23 Oct.! 997) overhead of 53-MHz VHF wind pro filer radar at Gadanki. The retrieved rain integral parameters were compared to the corresponding disdrometer data and a reasonably good agreement between the measurements has been found, lending credence to the VHF wind profiler radar retrievals of DSD parameters. Wind profi ler radar estimated DSD during stratiform precipitation has been compared with the lognormal Indian climate model. It is observed that the pattern of DSD agrees closely with both models.

The Measurement of Charge and Size of Raindrops: Part I. The Disdrometer

Abstract: An apparatus is described which enables reliable measurement of precipitation charge and size to be made. Design criteria are thoroughly treated and general solutions are provided to all aspects of the problem. The theories allow the performance of the apparatus in relation to drop splashing, drop overlap, and finite sampling time to be estimated with confidence. Full constructional details and performance of the apparatus and associated data storage equipment operating under strict laboratory conditions is given.

Evaluation of the reflectivity calibration of W-band radars based on observations in rain

Abstract: . This study presents two methods to evaluate the reflectivity calibration of W-band cloud radars. Both methods use natural rain as a reference target. The first approach is based on a self-consistency method of polarimetric radar variables, which is widely used in the precipitation radar community. As previous studies pointed out, the method cannot be directly applied to higher frequencies, where non-Rayleigh scattering effects and attenuation have a non-negligible influence on radar variables. The method presented here solves this problem by using polarimetric Doppler spectra to separate backscattering and propagational effects. New fits between the separated radar variables allow to estimate the absolute radar calibration using a minimization technique. The main advantage of the self-consistency method is its less dependence on the spatial variability in radar drop-size-distribution (DSD). The estimated uncertainty of the method is 0.7 dB. The method was applied to three intense precipitation events and the retrieved reflectivity offsets were within the estimated uncertainty range. The second method is an improvement of the conventional disdrometer-based approach, where reflectivity from the lowest range gate is compared to simulated reflectivity using surface disdrometer observations. The improved method corrects first for the time-lag between surface DSD observations and the radar measurements at a certain range. In addition, the effect of evaporation of raindrops on their way towards the surface is mitigated. The disdrometer-based method was applied to 12 rain events observed by vertically-pointed W-band radar and showed repeatable estimates of the reflectivity offsets at rain rates below 4 mm/h within 0.9 dB. The proposed approaches can analogously be extended to Ka-band radars. Although very different in terms of complexity, both methods extend existing radar calibration evaluation approaches, which are inevitably needed for the growing cloud radar networks in order to provide high-quality radar observation to the atmospheric community.

Optimal Determination of Parameters for Gamma-Type Drop Size Distributions Based on Moments

Abstract: Measured raindrop size distributions are often approximated by analytical functions. The parameters determining such functions are usually derived from measured data. This procedure can suffer from various uncertainties. The most important of which are (i) the limited detection range of measuring devices such as, for example, disdrometers, and (ii) poor statistics resulting from the rare appearance of relatively large drops.One way to derive the parameters is the moments method that has a degree of freedom in the choice of the moments. The aim of this study is to find an optimal choice of moments. To this end, numerical experiments are performed by calculating random samples from drop populations with gamma-shaped size distributions. These samples are evaluated as they were recorded by an ideal disdrometer whose single limitation is the cutoff with respect to very small and very large raindrops. From that data the parameters mentioned above are determined by the moments method. The truncation of t...