Showing papers on "Disdrometer published in 2012"

Sensitivity of a Simulated Midlatitude Squall Line to Parameterization of Raindrop Breakup

Abstract: This paper describes idealized simulations of a squall line observed on 20 June 2007, in central Oklahoma Results are compared with measurements from dual-polarization radar and surface disdrometer The baseline model configuration qualitatively reproduces key storm features, but underpredicts precipitation rates and generally overpredicts median volume raindrop diameter The sensitivity of model simulations to parameterization of raindrop breakup is tested under different low-level (0–25 km) environmental vertical wind shears Storm characteristics exhibit considerable sensitivity to the parameterization of breakup, especially for moderate (00048 s−1) shear Simulations with more efficient breakup tend to have higher domain-mean precipitation rates under both moderate and higher (00064 s−1) shear, despite the smaller mean drop size and hence lower mass-weighted fall speed and higher evaporation rate for a given rainwater content In these runs, higher evaporation leads to stronger cold pools,

A Climatology of Disdrometer Measurements of Rainfall in Finland over Five Years with Implications for Global Radar Observations

Abstract: To improve the understanding of high-latitude rain microphysics and its implications for the remote sensing of rainfall by ground-based and spaceborne radars, raindrop size measurements have been analyzed that were collected over five years with a Joss–Waldvogel disdrometer located in Jarvenpaa, Finland. The analysis shows that the regional climate is characterized by light rain and small drop size with narrow size distributions and that the mutual relations of drop size distribution parameters differ from those reported at lower latitudes. Radar parameters computed from the distributions demonstrate that the high latitudes are a challenging target for weather radar observations, particularly those employing polarimetric and dual-frequency techniques. Nevertheless, the findings imply that polarimetric ground radars can produce reliable “ground truth” estimates for space observations and identify dual-frequency radars utilizing a W-band channel as promising tools for observing rainfall in the high-...

Investigation of Rain Attenuation in Equatorial Kuala Lumpur

Abstract: This letter investigates rain attenuation in Kuala Lumpur, Malaysia, by exploiting local drop size distribution (DSD) measurements. Coefficients for the well-established power-law model relating rain rate and specific attenuation are derived for frequencies in the Ku-, Ka-, and Q/V-bands based on three years of disdrometer data. We analyze the diurnal variation of rainfall rate for four time intervals and, moreover, we present statistics of rain attenuation for slant-path Earth-space links estimated by means of a new model (Stratiform-Convective SST) that combines the advantages of the Dual-Layer Synthetic Storm Technique (SST) and the SC EXCELL model. The predicted statistics are in good agreement with those obtained from beacon measurements (MEASAT-1 satellite at 12 GHz). Finally, the diurnal variation of the slant-path rain attenuation is presented to provide system operators and radio communication engineers with useful information on the quality of service (QoS) that can be achieved during a typical day on an Earth-space link.

Estimating the Accuracy of Polarimetric Radar–Based Retrievals of Drop-Size Distribution Parameters and Rain Rate: An Application of Error Variance Separation Using Radar-Derived Spatial Correlations

Abstract: The accuracy of retrieving the two drop size distribution (DSD) parameters, median volume diameter (D0), and normalized intercept parameter (NW), as well as rain rate (R), from polarimetric C-band radar data obtained during a cool-season, long-duration precipitation event in Huntsville, Alabama, is examined. The radar was operated in a special “near-dwelling” mode over two video disdrometers (2DVD) located 15 km away. The polarimetric radar–based retrieval algorithms for the DSD parameters and rain rate were obtained from simulations using the 2DVD measurements of the DSD. A unique feature of this paper is the radar-based estimation of the spatial correlation functions of the two DSD parameters and rain rate that are used to estimate the “point-to-area” variance. A detailed error variance separation is performed, including the aforementioned point-to-area variance, along with variance components due to the retrieval algorithm error, radar measurement error, and disdrometer sampling error. The spat...

Influence of the Subgrid Variability of the Raindrop Size Distribution on Radar Rainfall Estimators

Abstract: This work aims at quantifying the variability of the parameters of the power laws used for rain-rate estimation from radar data, on the basis of raindrop size distribution measurements over a typical weather radar pixel. Power laws between the rain rate and the reflectivity or the specific differential phase shift are fitted to the measured values, and the variability of the parameters is analyzed. At the point scale, the variability within this radar pixel cannot be solely explained by the sampling uncertainty associated with disdrometer measurements. When parameters derived from point measurements are applied at the radar pixel scale, the resulting error in the rain amount varies between −2% and +15%.

Two Distinct Modes in One-Day Rainfall Event during MC3E Field Campaign: Analyses of Disdrometer Observations and WRF-SBM Simulation

Abstract: A unique microphysical structure of rainfall is observed by the surface laser optical Particle Size and Velocity (Parsivel) disdrometers on 25 April 2011 during Midlatitude Continental Convective Clouds Experiment (MC3E). According to the systematic differences in rainfall rate and bulk effective droplet radius, the sampling data can be divided into two groups; the rainfall mostly from the deep convective clouds has relatively high rainfall rate and large bulk effective droplet radius, whereas the reverse is true for the rainfall from the shallow wrm clouds. The Weather Research and Forecasting model coupled with spectral bin microphysics (WRF-SBM) successfully reproduces the two distinct modes in the observed rainfall microphysical structure. The results show that the up-to-date model can demonstrate how the cloud physics and the weather condition on the day are involved in forming the unique rainfall characteristic.

Microphysical characteristics of the raindrop size distribution in typhoon morakot （2009）

Abstract: Microphysical characteristics of the raindrop size distribution(RSD)in Typhoon Morakot(2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province,China during the passage of the storm from 7 to 10 August 2009.The time evolution of the RSD reveals different segments of the storm.Significant difference was observed in the microphysical characteristics between the outer rainband and the eyewall;the eyewall precipitation had a broader size distribution(a smaller slope) than the outer rainband and eye region.The outer rainband and the eye region produced stratiform rains while the eyewall precipitation was convective or mixed stratiform-convective.The RSD was typically characterized by a single peak distribution and well represented by the gamma distribution.The relations between the shape(μ)and slope(Λ)of the gamma distribution and between the reflectivity(Z)and rainfall rate(R)have been investigated.Based on the NW-Dm relationships,we suggest that the stratiform rain for the outer rainband and the eye region was formed by the melting of graupel or rimed ice particles,which likely originated from the eyewall clouds.

Analysis of measured drop size spectra over land and sea

Abstract: Drop size spectra were measured by using an optical disdrometer of type ODM 470 at different locations. They were subdivided in to four data sets: measurements over land, in coastal areas, over semienclosed seas, and over the open sea. Based on 1-minute measurement intervals, no differences were found in drop size spectra between continental and maritime areas. An exponential model with a rain rate depending on interception number and prefactor in the exponent fits well the spectra, and maximum drop sizes depend strongly on estimated rain rates. In contrast to other investigations, there are no significant differences between spectra of convective and stratiform rain based on 1-minute measurement intervals. However, spectra integrated over 10 minutes show the expected differences.

The measurement of rain kinetic energy and rain intensity using an acoustic disdrometer

Abstract: Microwave engineers and geomorphologists require rainfall data with a much greater temporal resolution and a better representation of the numbers of large raindrops than is available from current commercial instruments. This paper describes an acoustic instrument that determines rain parameters from the sound of raindrops falling into a tank of water. There is a direct relationship between the kinetic energy (KE) of a raindrop and the acoustic energy that it creates upon impact. Rain KE flux density is estimated from measurements of the sound field in the tank, and these have been compared to measurements from a co-sited commercial disdrometer. Eight months of data have been collected in the eastern UK. Comparisons of rain KE estimated by the two instruments are presented and links between the KE and rainfall intensity are discussed. The sampling errors of the two instruments are analysed to show that the acoustic instrument can produce rain KE measurements with a 1 s integration time with sampling uncertainty of the same size as commercial instruments using a 1 min integration time.

Phase space parametrization of rain: the inadequacy of the gamma distribution

Abstract: We show that the Gamma distribution is not an adequate fit for the probability density function of drop diameters using the Kolmogorov-Smirnov goodness of fit test. We propose a different parametrization of drop size distributions, which not depending by any particular functional form, is based on the adoption of standardized central moments. The first three standardized central moments are sufficient to characterize the distribution of drop diamters at the ground. These parameters together with the drop count form a 4-tuple which fully describe the variability of the drop size distributions. The Cartesian product of this 4-tuple of parameters is the rainfall phase space. Using disdrometer data from 10 different locations we identify invariant, not depending on location, properties of the rainfall phenomenon.

Altitudinal and temporal evolution of raindrop size distribution observed over a tropical station using a K-band radar

Abstract: Rain drop size distribution (DSD) measurements at different heights were made using a micro rain radar (MRR) at Thiruvananthapuram (latitude: 8.3° N, longitude: 76.9° E). Rain DSD data obtained from the MRR have been compared with a Joss–Waldvogel impact-type disdrometer (RD-80) deployed nearby and found to have good agreement. The analysis uses data collected during 16 continuous rainfall episodes during the southwest monsoon (June to September, JJAS) season. Since all the episodes behaved similarly, a single continuous rainfall episode occurring from 1610:01 to 1612:31 hours Indian Standard Time (IST) on 12 August 2006 is presented here. The fall velocity of those drops that contributed most to the rain rate was more or less constant at different altitudes and also with time during this episode, and the average value was 4.65 m s−1. The rain rate (RR) was below 5 mm h−1 for all the heights throughout the time. At the beginning of the rain episode, the number of drops at any given altitude was lower for ...

Regime analysis of rainfall drop-size distribution models for microwave terrestrial networks

Abstract: In this study, parameters of statistical models for estimating the rainfall specific attenuation in Durban, South Africa are derived. The rainfall data in this work are based on 2-year measurements obtained via the Joss-Waldvogel RD-80 disdrometer between January 2009 and December 2010. Four rainfall regimes are applied: drizzle, widespread, shower and thunderstorm types. Using the third, fourth and sixth moments of the measured data, estimators for four rainfall drop-size distribution (DSD) models - 3-parameter lognormal model, negative exponential model, 3-parameter Weibull model and the modified gamma model - are computed. The specific attenuation estimates from our model are compared with the values from predicted measurements alongside the International Telecommunication Union (ITU) estimates for frequencies between 2 and 100-GHz. The results from the specific attenuation estimation are compared with the semi-empirical measurements for their respective regimes using root-mean-square and X 2 error tests. From the results, the best models for the various regimes are: Weibull model for drizzle regime, modified gamma model for widespread and shower regimes and lognormal model for the thunderstorm regime.

Microphysical characteristics of the raindrop size distribution in typhoon morakot(2009)

Abstract: Microphysical characteristics of the raindrop size distribution(RSD)in Typhoon Morakot(2009) have been studied through the PARSIVEL disdrometer measurements at one site in Fujian province,China during the passage of the storm from 7 to 10 August 2009.The time evolution of the RSD reveals different segments of the storm.Significant difference was observed in the microphysical characteristics between the outer rainband and the eyewall;the eyewall precipitation had a broader size distribution(a smaller slope) than the outer rainband and eye region.The outer rainband and the eye region produced stratiform rains while the eyewall precipitation was convective or mixed stratiform-convective.The RSD was typically characterized by a single peak distribution and well represented by the gamma distribution.The relations between the shape(μ)and slope(Λ)of the gamma distribution and between the reflectivity(Z)and rainfall rate(R)have been investigated.Based on the NW–Dm relationships,we suggest that the stratiform rain for the outer rainband and the eye region was formed by the melting of graupel or rimed ice particles,which likely originated from the eyewall clouds.

Skewness as measure of the invariance of instantaneous renormalized drop diameter distributions – Part 1: Convective vs. stratiform precipitation

Abstract: We investigate the variability of the shape of the renormalized drop diameter instantaneous distribution using of the third order central moment: the skewness . Disdrometer data, collected at Darwin Australia, are considered either as whole or as divided in convective and stratiform precipitation intervals. We show that in all cases the distribution of the skewness is strongly peaked around 0.64. This allows to identify a most common distribution of renormalized drop diameters and two main variations, one with larger and one with smaller skewness. The distributions shapes are independent from the stratiform vs. convective classification.

Low‐cost laser disdrometer with the capability of hydrometeor imaging

Abstract: Precision of microwave precipitation remote sensing is ensured by studying different hydrometeor classes (raindrops, snowflakes, graupel, and so on), shapes, and drop size distribution (DSD). Recently, DSD estimates and hydrometeor classification algorithms using polarimetric radars were proposed. These algorithm developments require a validation tool providing in situ hydrometeor measurement. We are working toward the development of a low-cost, light-weight, and disposable ballooning hydrometeor imaging probe with DSD measurement capabilities. This paper describes the performance of a new line-scanning laser hydrometeor imaging probe (called PROBE) and validates the DSD using a commercially available impact-type disdrometer. PROBE captures raindrop images with 0.125 mm horizontal resolution and more than six slices at the 33-kHz slice rate, providing a reasonable raindrop diameter. DSD validation shows that PROBE acquires adequate DSD shapes during every 2-min interval. These results demonstrate PROBE's performance in hydrometeor imaging and DSD measurement capabilities in a rainfall. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Skewness as measure of the invariance of instantaneous renormalized drop diameter distributions - Part 2: Orographic precipitation

Abstract: Here we use the skewness parameter, and the procedure developed in the companion paper (Ignaccolo and De Michele, 2012), to investigate the variability of instantaneous renormalized spectra of rain drop diameter in presence of orographic precipitation. Disdrometer data, available at Bodega Bay and Cazadero, California, are analyzed either as a whole, or as divided (using the bright band echo) in precipitation intervals weakly and strongly influenced by orography, and compared to results obtained at Darwin, Australia. We find that also at Bodega Bay and Cazadero exists a most common distribution of the skewness values of instantaneous spectra of drop diameter, but peaked at values greater than 0.64, found at Darwin. No appreciable differences are found in the skewness distributions of precipitation weakly and strongly influenced by orography. However the renormalized drop diameter spectra of precipitation with strong orographic component have fatter right tail than precipitation with a weaker orographic component. The differences between orographic and non-orographic precipitation are investigated within the parametric space represented by number of drops, mean value and standard deviation of drop diameter. A filter is developed which is able to identify 1 min time intervals during which precipitation is mostly of orographic origin.

Estimation of rain kinetic energy from radar reflectivity and/or rain rate based on a scaling formulation of the raindrop size distribution

Abstract: [1] This study offers an approach to estimate the rainfall kinetic energy (KE) by rain intensity (R) and radar reflectivity factor (Z) separately or jointly on the basis of a one- or two-moment scaled raindrop size distribution (DSD) formulation, which contains (1) R and/or Z observations and (2) the dimensionless probability density function (pdf) of a scaled raindrop diameter. The key point is to explain all variability of the DSD by the evolution of the explaining moments (R and Z); hence the pdf is considered as constant. A robust method is proposed to estimate the climatological values of the parameters with a 28 month DSD data set collected in the Cevennes-Vivarais region of France. Three relationships (KE-R, KE-Z, and KE-RZ), which link the observations (R and/or Z) to rainfall kinetic energy (KE), are established. As expected, the assessment using the disdrometer data indicates that (1) because of the proximity of the moment orders, the KE-Z relationship exhibits less variability than the KE-R relationship and (2) the combination of R and Z yields a significant improvement of the estimation of KE compared to the single-moment formulations. Subsequently, a first attempt to spatialize the kinetic energy using radar and rain gauge measurements is presented for a convective event, showing a promising potential for erosion process studies. Different from the application with the disdrometer data, the performance of the KE-Z relationship degrades compared to the KE-R relationship as a result of a bias and/or the sampling characteristics of the radar data.

Characterization and Design of a Readout Circuit for a Piezoelectric-based Acoustic Disdrometer

Abstract: In 2009, Department of Water Management (DWM) at TU Delft conceptualized the design of a low-cost disdrometer suitable for large scale, remote deployment. But, being a novel idea, its electrical characteristics were not well researched. Also, the system was not sensitive enough to measure the raindrops of diameter less than 0.9mm. Furthermore, it was found that the proposed disdrometer suffers from the edge effect i.e. when a raindrop hits on the edge of the disdrometer; the size of the raindrop is underestimated. All the aforementioned issues have been addressed in this research. The presented work discusses the electrical characteristics of the disdrometer. A readout circuit has been designed to improve the performance of the disdrometer and an innovative technique has been developed to solve the problem of edge effect. The impedance response of the disdrometer has been analyzed and an equivalent electrical model of the proposed disdrometer has been developed and characterized. Furthermore, an elaborative analysis of the edge effect has been presented. Based on this analysis, an innovative technique has been proposed for reducing the edge-effect. This technique uses the envelope of the transducer’s output to determine if the drop hit on edge. Also, a low-power (17.8mA@5V), low-noise (7.8µVrms) readout circuit has been designed. This readout circuit is able to measure the drops of size as low as 0.4mm. Because of the achieved results, this disdrometer is attracting a lot of attention of various groups from industry as well as from academia. A group of researchers from the DWM, TU Delft is looking forward to turn it in to a commercial product.

Effect of sampling variation on error of rainfall variables measured by optical disdrometer

Abstract: . During the sampling process of precipitation particles by optical disdrometers, the randomness of particles and sampling variability has great impact on the accuracy of precipitation variables. Based on a marked point model of raindrop size distribution, the effect of sampling variation on drop size distribution and velocity distribution measurement using optical disdrometers are analyzed by Monte Carlo simulation. The results show that the samples number, rain rate, drop size distribution, and sampling size have different influences on the accuracy of rainfall variables. The relative errors of rainfall variables caused by sampling variation in a descending order as: water concentration, mean diameter, mass weighed mean diameter, mean volume diameter, radar reflectivity factor, and number density, which are independent with samples number basically; the relative error of rain variables are positively correlated with the margin probability, which is also positively correlated with the rain rate and the mean diameter of raindrops; the sampling size is one of the main factors that influence the margin probability, with the decreasing of sampling area, especially the decreasing of short side of sample size, the probability of margin raindrops is getting greater, hence the error of rain variables are getting greater, and the variables of median size raindrops have the maximum error. To ensure the relative error of rainfall variables measured by optical disdrometer less than 1%, the width of light beam should be at least 40 mm.

ARM - Midlatitude Continental Convective Clouds Experiment (MC3E): Multi-Frequency Profilers, Parcivel Disdrometer (williams-disdro)

Abstract: This data was collected by the NOAA 449-MHz and 2.8-GHz profilers in support of the Department of Energy (DOE) and NASA sponsored Mid-latitude Continental Convective Cloud Experiment (MC3E). The profiling radars were deployed in Northern Oklahoma at the DOE Atmospheric Radiation Mission (ARM) Southern Great Plans (SGP) Central Facility from 22 April through 6 June 2011. NOAA deployed three instruments: a Parsivel disdrometer, a 2.8-GHz profiler, and a 449-MHz profiler. The parasivel provided surface estimates of the raindrop size distribution and is the reference used to absolutely calibrate the 2.8 GHz profiler. The 2.8-GHz profiler provided unattenuated reflectivity profiles of the precipitation. The 449-MHz profiler provided estimates of the vertical air motion during precipitation from near the surface to just below the freezing level. By using the combination of 2.8-GHz and 449-MHz profiler observations, vertical profiles of raindrop size distributions can be retrieved. The profilers are often reference by their frequency band: the 2.8-GHz profiler operates in the S-band and the 449-MHz profiler operates in the UHF band. The raw observations are available as well as calibrated spectra and moments. This document describes how the instruments were deployed, how the data was collected, and the format of the archived data.

Variability of raindrop size distribution and its impact on polarimetric rain rate estimators

Abstract: Four years of raindrop size distribution (DSD) by Joss-Waldvogel (JW) Disdrometer measurements made at Gadanki (13.5°N, 79.2°E) have been used to derive relations for rainfall estimation from polarimetric radar variables. The polarimetric variables are estimated in X-band (at 9.368 GHz, the chosen frequency for the radar being developed at Gadanki) from the observed DSD measurements and scattering amplitudes derived using T-matrix scattering simulations. Three rainfall estimators, namely R-Z, R-KDP and R-(ZH, ZDR), are derived for both stratiform and convective types of rain. Also, following the earlier reports, which highlighted the large variability of DSD between the seasons, the above relations are derived for three seasons (pre-monsoon, southwest monsoon and northeast monsoon). The scatter plots of R and Z show large scatter around the regression fits, even after separating the data into different seasons and types of rain, indicating the large and complex variability of DSD. Among all the relations, R-Z relation depends heavily on the DSD with its coefficients vary significantly between the seasons and types of rain. The other two relations show weak dependency on DSD, however, the coefficients are found to be distinctly different from those reported elsewhere. Both qualitative and quantitative evaluation analyses on a case study reveal that R-(ZH, ZDR) relation provides better R among the three relations.

Usefulness of dual-frequency precipitation SAR (PSAR) for next-generation space-based precipitation mission

Abstract: Basic system design of dual-frequency (13.6/35.5 GHz) Precipitation SAR (PSAR) is described, which is based on the orbit parameters of the GPM core satellite. The designed PSAR requires the along-track antenna size of about 4 m at both frequencies which are about twofold (13.6 GHz) and four-fold increase (35.5 GHz) compared with the DPR antennas. Instead of this, along-track resolution could be drastically improved to about 0.7 km in comparison with that of GPM-DPR (5 km). It also has reasonable number of independent samples for incoherent averaging (50~70), and swath width (~180 km) with the cross-track resolution of 2.5 km. Effects of apparent beam shift and the beam smearing caused by the spread of raindrop terminal velocity spectrum, inherent problems in PSAR, are quantitatively studied using a large number of disdrometer samples. The along-track beam shift of rain echo could also be used to estimate path-averaged raindrop fall velocity. Finally various issues in the system development and usefulness of the PSAR are discussed.

Variability of Rain Microphysics Using Long-term Disdrometer Observations

Abstract: This study explores variability of rain microphysics in terms of drop size distributions (DSD) using seven years of Joss-Waldvogel disdrometer data in a long-term perspective Firstly, self-consistency evaluation of the disdrometer is performed against four raingauges The result indicates that the disdrometer derived rain totals are in a good agreement to the raingauges with correlation coefficients ranging from 089 to 099 In addition, a total of 162 415 one-minute filtered raindrop spectra obtained from the disdrometer are fitted to the normalized gamma DSD model to understand DSD variability in different seasonal and atmospheric states To characterize rain microphysics, four sets of DSDs are created from the entire raindrop spectra – two are based on seasonal “equinox” criteria and the other two are based on wet bulb temperature It has been revealed that the normalized gamma DSD parameters, Nw, Dm, and μ vary from set to set because of seasonal and atmospheric variability Finally, radar Z-R relations for the four DSD sets are developed and it is shown that coefficients differ meaningfully from state to state In particular, the variability is found to be more substantial between those DSDs which have been separated using the wet bulb temperature

Effect of R-Z Relationships Derived from Disdrometer Data on Radar Rainfall Estimation during the Heavy Rain Event on 5 July 2005

Abstract: The R-Z relationship is one of important error factors to determine the accuracy of radar rainfall estimation. In this study, we have explored the effect of the R-Z relationships derived from disdrometer data in estimating the radar rainfall. The heavy rain event that produced flooding in St-Remi, Quebec, Canada has been occurred. We have tried to investigate the severity of rain for this event using high temporal (2.5 min) and spatial resolution ( by 250 m) radar data obtained from the McGill S-band radar. Radar data revealed that the heavy rain cells pass directly over St-Remi while the coarse raingauge network was not sufficient to detect this rain event. The maximum 30 min (1 h) accumulation reaches about 39 (42) mm in St-Remi. During the rain event, the two disdrometers (POSS; Precipitation Occurrence Sensor System) were available: One used for the reflectivity calibration by comparing disdrometer Z and radar Z and the other for deriving disdrometric R-Z relationships. The result shows the significant improvement with the disdrometric reflectivity-dependent R-Z relationships against the climatological R-Z relationship. The bias in radar rain estimation is reduced from +12% to -2% and the root-mean squared error from 16 to 10% for daily accumulation. Using the estimated radar rainfall rate with disdrometric R-Z relationships, the flood event was well captured with proper timing and amount.

Determining Wind Velocity from Images of Raindrops

Abstract: This study develops the method of determining wind velocity from images of raindrops. The motivation of this study was to develop a new method of finding wind velocity. In this new method, digital images or videos of raindrops are processed using computer stereo vision to extract information about the rain inclination. The rain inclination is then used to compute the wind velocity. The rain inclination changes with height (and time) due to acceleration from the force exerted by the wind on the raindrops. A simple experiment was conducted to demonstrate that it is possible to determine rain inclination from digital images. The inclination of falling water was found using two perpendicular two-dimensional digital images. This implies that it is possible to determine rain inclination from digital images. Some equations relating wind velocity and the trajectory of a raindrop are derived using Stokes’ Law. Extensive use of fluid mechanics is required to derive accurate equations. Some hypothetical setups of systems that use this method are described. Wind velocity can also be determined from stereoscopic videos of raindrop trajectory. Disdrometers may be used instead of digital cameras when applying this method. Keywords: rain inclination, raindrop, wind velocity, camera, digital images, stereoscopic vision, computer stereo vision, epipolar geometry, wind force, disdrometer, pinhole camera model, fluid mechanics.

A redesigned instrument and new data analysis method used to measure the size and velocity of hydrometeors

Abstract: A redesigned instrument and new data analysis method used to measure the size and velocity of hydrometeorsA redesigned instrument and new data analysis method used to measure the size and velocity of hydrometeors." ii To My Family and Friends iii Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it. iv ACKNOWLEDGMENTS First, I would like to thank my family and friends for their support and patience during this project. Also, I would like to thank Bill for his support during the duration of this project. He offered many ideas and solutions to problems that made this project possible. Table 6-A table breaking down the number of simultaneous drops in the sample area and the number of drops smaller than 0. Figure 7-The design of the housing constructed from copper. The laser head and detector head are made out of 2 ½ inch copper tubing. The frame is constructed from ½ inch copper tubing. The base is constructed from solid stock of 1 inch thick copper.. Figure 9-A sample of raw data as a steel sphere passes through the sample area. The two pulsed signals correspond to the raindrop passing through and blocking the first laser sheet and second laser sheet, Figure 10-Cosine functions fitted to the pulsed signals generated by a steel sphere. If the sheet lasers were infinitely thin the pulsed signals would fit the cosine curves.. Figure 11-An example of a pulsed signal produced by a sphere with a diameter smaller than the thickness of a laser sheet.. Figure 13-An example of the tails produced by a spherical hydrometeor passing through a laser sheet that has a thickness. Figure 14-An inverted and normalized data sample showing the parameters obtained from the raw data. The lag time (t lag) is the time it takes the hydrometeor to travel from the center of one laser sheet to the center of the other. The time of attenuation (t att) is the cumulative time it takes a hydrometeor to pass through one laser sheet. The time of attenuation can be measured twice from the two pulsed signalls. t att1 corresponds to the first pulsed signal, and t att2 corresponds to the second pulsed ix Figure 15-An inverted and normalized data sample showing the parameters obtained from the raw data. The lag time (t lag) is the time it …