Dissertations / Theses on the topic 'Disdrometer'

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 thesis describes the development of an acoustic instrument that determines rain parameters from the sound of raindrops falling into a tank of water. It is known as the acoustic water tank disdrometer (AWTD).There is a direct relationship between the kinetic energy of a raindrop and the acoustic energy generated upon impact. Rain kinetic energy flux density (KE) is estimated from measurements of the sound field in the tank and these have been compared to measurements from a co-sited commercial disdrometer.Furthermore, using an array of hydrophones it is possible to determine the drop size and impact position of each raindrop falling into the tank. Accumulating the information from many impacts allows a drop size distribution (DSD) to be calculated.Eight months of data have been collected in the eastern UK. The two methods of parameter estimation are developed and analysed to show that the acoustic instrument can produce rain KE measurements with a one-second integration times and DSDs with accurate large drop-size tails.

This thesis considers the problem of estimating the three parameters of a gamma distribution with grouped and truncated data. Sample sizes may be small and commonly subject to lower and perhaps upper truncation. A new simple, closed form, rehable. almost unbiased and low-variance method is developed. It is shown that the new 'hybrid' approach is a first order approximation to maximum like.hood with a constraint that incorporates a single sample moment ratio. Traditional moment methods require three distinct sample moments and typically give ised estimates. The operation of the hybrid method is discussed and extended to encompass the estimation of parameters for a Generalized Gamma mode.

The aim of the present Thesis is to observe the characteristics of the precipitation and to check the quality of the radar data under different meteorological conditions. This aim is achieved through a combined analysis of the data collected by two instruments that have different operating principles: a C-band polarimetric radar and a PARSIVEL2 disdrometer. Radar variables are compared with the characteristics and the microphysics evolution of the precipitation retrieved by the disdrometer. The disdrometer is located in the city center of Bologna, at about 28 km far from the radar site. The combined analysis of the two instruments is done for a dataset that includes 11 months of the years 2019 and 2020. The dataset contains convective and stratiform precipitation events. The lower radar elevations are affected by anthropogenic interferences that slightly reduce the dataset extension. The analyses show a good correlation between the reflectivity factors retrieved by the radar and by the disdrometer through the Drop Size Distribution (DSD). The correlation coefficient between the two estimations is 0.84. A verification of the operational algorithm of the hydrometeor classification is obtained through the radar data. Moreover, the convective and stratiform discrimination developed through the disdrometer data is consistent with the polarimetric variables of the radar. For example, the distribution of the differential reflectivity peaks for higher values in a regime of convective precipitation in comparison to the stratiform regime. The convective distribution of the differential reflectivity has a median of 1.5 dB, while the stratiform one has a median of 0.9 dB. Lastly, the case study of a thunderstorm occurred in Bologna on May 28th 2019 is described. This case study shows precipitation structures of different intensities and different types of hydrometeors, allowing a verification of the previous results and a more-detailed analysis of the DSD characteristics.

Nederbördsmätning är viktigt inom många områden och en relativt ny teknik är enoptisk distrometer som med hjälp av laserteknik mäter nederbördspartiklarnasdroppstorlek och fallhastighet. Syftet med detta arbete var att undersöka hur välThies distrometer stämmer överens med nederbördsmätning från ett vippkärl ochmanuella mätningar från institutionen för geovetenskaper vid Uppsala universitet.Institutionen för geovetenskaper överväger att gå över till denna teknik och därmedbehövdes distrometern utvärderas för olika faktorer som kan påverka instrumentet.Vid jämförelse mellan instrumenten visade det sig att distrometern totalt sett samladein mer nederbörd än de andra mätarna. Det är svårt att avgöra vad skillnaden mellaninstrumenten kan bero på men felkällor så som avdunstning och vätning hos vippkärletoch manuella mätningar kan ge mindre nederbörd. En annan orsak kan varafelkalibrering av datan från distrometern. Inga samband hittades för vindhastighet,vindriktning och typ av nederbörd mellan de tre instrumenten. En vidare undersökning gjordes för droppstorleksfördelningen för att ge exempelpå fördelar med en distrometer. Droppstorleksfördelningen från distrometernjämfördes med exponentialfördelningen framtagen av Marshall & Palmer (1948).Resultatet visade sig stämma överens med tidigare studier, fördelningen stämmerbra överens för stratiforma väder, men sämre för konvektiva och snö.
Measuring precipitation is important in many areas of research. A relatively newtechnology for measuring precipitation is the optical disdrometer, which measures thefalling velocity and drop size of particles by using lasers. The purpose of this workwas to compare data from a disdrometer with data from a tipping bucket and amanual measurement series from the Department of Earth Sciences at UppsalaUniversity. The comparison between the instruments showed that the disdrometermeasured more precipitation than the tipping bucket and the manual measurements.A reason for this can be due to evaporation and wetting from the tipping bucket andmanual measurement. Errors in calibration of data from the disdrometer may alsohave influence. Furthermore, an analysis of the drop size distribution was done in order todetermine areas of special use for the device. The drop size distribution calculatedfrom the distrometer was compared with the Marshall and Palmer (1948) distribution.The results showed that the MP-distribution was a good fit for stratiform weather;however, for convective clouds and snow the fit was not satisfactory and some otherrelationship should be used instead.

Vindtunneln som drivs av Sports Tech Research Centres   är en unik anläggning för att bedriva forskning på både atletiska utövare och   utrustning. Vindtunnelns avancerade system möjliggör för forskning och tester   på material och produkter kan utföras i en verklighetstrogen miljö. Det finns   även sedan byggnationen ett regnsystem installerat i vindtunneln. Detta   system är inte uppmätt efter viktiga faktorer och ingen vetskap om det   simulerade regnets egenskaper eller likhet med naturligt förekommande regn   finns. Syftet med arbetet var att utföra mätningar på det   befintliga regnsystemet med avseende på storlek och fallhastighet för   dropparna. Arbetets syfte var även att jämföra de uppmätta regn egenskaperna   mot vetenskapliga modeller som beskriver ett naturligt regn. Där målet med   arbetet var att ta fram ett underlag på det befintliga regnet i vindtunneln. Testerna utfördes med en optisk distrometer som   mätte de fallande vattendropparna med en laser. Distrometern användes för att   mäta storlek samt fallhastighet på vattendropparna. Distrometer placerades   vid tester på olika höjder i vindtunneln, regnet undersöktes även vid   varierande vattenflöde och vindhastigheter. Resultatet visade på att simulerade regnet hade en   lägre hastighet i förhållande till den uppmätta droppstorleken högt i   tunneln. Hastigheten på dropparna lågt i tunneln visade mer följa modellernas   beskrivning av en naturligfallhastighet. Droppstorleksfördelningen visades   inte överstämma mot naturligt regn utan visar på en högre mängd stora droppar   än vad som är naturligt förekommande. Intensiteten i vindtunneln var som   lägst 62 mm/h vilket väldigt högt sett från naturligt regn. Utifrån dessa   parametrar följer inte det simulerade regnet ett naturligt förekommande regn.
The wind tunnel operated by Sport Tech Research Centres,   are a unique facility to conduct research on athletic practitioners and their   equipment. The advanced systems in the wind tunnel allows for research and   testing of materials and product in a realistic environment. Since the   construction of the wind tunnel a rain system was fitted. This system is not   measured for important factors and no knowledge of the simulated rainfall   properties or similarities to naturally occurring rain exists. The aim of this work was to perform measurements of   the existing rainfall system with regards to size and falls speed of the   droplets. The purpose was also to compare the measure rain properties to   scientific models describing natural rainfall. The goal of the work was to   get a foundation of the existing rain in the wind tunnel. The tests were performed with an optic disdrometer   that measured the falling water particles with a laser. The disdrometer   measured size and fall speed of the droplets. The tests were carried out on   different heights in the wind tunnel, the rain was also investigated at   varying water pressure and wind speeds. The result shows that the simulated rainfall had   lower speed relative to the measured drop size high in the tunnel. Fall speed   of droplets low in the tunnel showed more according to the model’s   description of a natural rain fall speed. Drop size distribution was shown   not to be consistent with natural rainfall. The distribution shows a higher   amount of large drops than is naturally occurring. Rainfall intensity was   measured to 62 mm/h as lowest which is very high compared to natural rain.   Based on these parameters the simulated rain is not a naturally occurring   rainfall.

Betyg: 180803

The primary mass input of the Antarctic ice sheet is represented by snow precipitation. Despite of their crucial role, the estimates of precipitation over Antarctica are sparse and characterized by large uncertainties. Recently, the Italian Mario Zucchelli station (MZS) at Terra Nova Bay was equipped with instruments for monitoring precipitation. This thesis is part of the APP-PNRA project (Antarctic precipitation properties from ground-based instruments), whose object is to set up an observatory to characterize precipitation at MZS. The present study was focused on the evaluation of the response of solid hydrometeors to the electromagnetic radiation and on the microphysical characterization of precipitation. The former was investigated using a pre-computed discrete dipole approximation (DDA) database for complex-shape snowflakes and a T-Matrix code for soft-spheroids. The backscattering cross sections, calculated at the K-band by the two methods, were compared. In case of aggregate particles the methods show a poor agreement, comparable values were found when pristine crystals were considered. The latter was examined through in-situ observations by a Parsivel disdrometer and Micro Rain Radar. By exploiting the Parsivel data collected during the summer seasons 2016-17 and 2017-18, the particle size distributions (PSD) of hydrometeors were derived, showing a high number of particles with very small diameter. Numerical simulations, driven by DDA and T-Matrix, were also performed by using the PSDs, to obtain the simulated radar reflectivity. The comparative analysis of simulated and actual reflectivity allowed inferring microphysical characterization of precipitation. Based on this methodology, 16 out of 22 snow days were categorized: 6 as having aggregate-like features and 10 as pristine crystal-like. These results will be of practical interest, giving an important contribution toward a more accurate quantification of snow accumulation in Antarctica.

En cas de rejets de polluants ou de radionucléides dans l’atmosphère, l’estimation du lessivage des particules d’aérosol atmosphérique par les précipitations est une donnée essentielle pour évaluer la contamination de la biosphère. De nombreuses études se sont déjà intéressées à ce processus de dépôt humide, mais la plupart d’entre elles sont d’ordre théoriques ou ont été menées en laboratoire. Cette étude a donc pour objectif d’améliorer la connaissance du potentiel de lessivage des particules d’aérosol par les précipitations par une approche expérimentale en conditions in situ. Durant plusieurs mois, trois sites aux environnements distincts en termes de climatologie et d’empoussièrement ambiant ont été instrumentés pour disposer d’une palette de situations précipitations/empoussièrement la plus variée possible. Un disdromètre laser et un granulomètre (compteur électrique et/ou optique) ont mesurés respectivement les caractéristiques des précipitations et les concentrations de particules à une résolution temporelle élevée et sur une large gamme de diamètre. L’utilisation de ce couplage instrumental original a permis de déterminer les potentiels de lessivage pour des particules de la gamme nanométrique à supermicronique et pour différents types de précipitations (chutes de neige et pluies avec des hyétogrammes spécifiques). Dans un premier temps, le coefficient de lessivage ᴧ (paramètre décrivant la cinétique du processus) a été calculé en considérant l’effet global d’une précipitation. Cette approche « macroscopique » est limitée par l’influence de processus « concurrents », tels que l’advection ou les sources d’émissions de particules à proximité des sites de mesures. Pour minimiser l’impact de ces processus sur nos résultats, une seconde méthodologie basée sur la résolution temporelle élevée de l’instrumentation utilisée a été définie. Par cette approche « intra-évènementielle », les coefficients de lessivage ᴧ sont calculés sur de courtes périodes de temps, permettant ainsi d’étudier l’influence de la variabilité du diamètre des particules et des caractéristiques des précipitations sur ces coefficients. Les résultats obtenus par les deux types d’approches ont mis en évidence la nécessité de prendre en compte le diamètre des particules et les caractéristiques des précipitations pour modéliser fidèlement le lessivage des particules d’aérosol atmosphérique. En comparant les résultats des deux types de précipitations, la prédominance du lessivage par des chutes de neige par rapport au lessivage par la pluie a été illustrée. L’importance du diamètre des particules lessivées a été démontrée. Entre le mode « ultrafin » et le mode « grossiers », la variation du coefficient de lessivage est d’un ordre de grandeur (entre environ 2.10¯³et 2.10¯⁴ s¯¹). Le potentiel de lessivage minimum est obtenu pour des particules d’environ 100 nm, ce qui est cohérent avec la théorie du « Greenfield gap » (entre 0,1 et 1 µm). Pour les besoins de la modélisation, une paramétrisation robuste entre le coefficient de lessivage ᴧ et le diamètre des particules d’aérosol (de 10 nm à 10 µm) a été établie. Différentes relations entre le coefficient ᴧ et l’intensité pluviométrique sont proposées aussi pour différentes gammes de diamètre de particules et comparées notamment aux valeurs implémentées actuellement dans le modèle ldX utilisé à l’Institut de Radioprotection et de Sûreté Nucléaire
In case of release of pollutant or radionuclides into the atmosphere, estimate of below-cloud scavenging of aerosol particles by precipitation (or washout) is an essential data to evaluate contamination of the biosphere. Many studies have already shown an interest to this wet deposition process, but most of them are theoretical or have been conducted in laboratories conditions. This study in situ conditions aims to improve knowledge of below-cloud scavenging of aerosol particles by precipitation. For several months, three sites with separate environments in terms of climate and ambient dust have been instrumented to have such a varied palette of precipitation/dust conditions as possible. A laser disdrometer and a granulomètre (electrical and/or optical counter) measure respectively precipitations characteristics and particles concentrations with a high temporal resolution (one minute). The use of this original instrumental coupling has allowed determining washout potentials for the nanometric size range of particles aerosol to the supermicronique size range and for different types of precipitation (snowfalls and rainfalls with specifics hyetograms).Initially, below-cloud scavenging coefficients ᴧ (parameter describing kinetic of this process) were calculated considering the gobal effet of a precipitation. This “macroscopic” approach is limited by the influence of “concurrent” processes, as advection or local emissions of aerosol particles close to the measurements sites. To minimise effect of these processes on our results, a second methodology based on the high temporal resolution of the instrumentation used was defined. With this “intra-event” approach, washout coefficients are calculated on short time scales, allowing study of impact of the variability of aerosol size and precipitations characteristics on these coefficients.Results obtained with the two approaches highlighted the need of considering particles diameter and characteristics of precipitation to model accurately below-cloud scavenging of aerosol particles. Comparing results for both type of precipitation, predomination of below-cloud scavenging by snowfalls compared with below-cloud scavenging by rainfalls was shown. The importance of the scavenged aerosol diameter was demonstrated. From the “ultrafine” size range to coarse mode of particles, below-cloud scavenging coefficient varies by an order of magnitude (from 2.10¯³ to 2.10¯⁴ s¯¹). Minimum potential is obtained for particles of about 100 nm, which is consistent with theory of “Greenfield gap” (from 0.1 to 1 µm). For modeling needs, a robust parametrization between washout coefficient ᴧ and aerosol particles diameter (from 10 nm to 10 µm) has been established. Also some relationships between coefficient ᴧ and rainfall intensity are proposed for different particles size range and compared in particular with values implemented in model ldX currently used at the French Institute of Radioprotection and Nuclear Safety

Les panaches volcaniques de téphras constituent un des aléas volcaniques majeurs. Pour prévoir leur dispersion et les zones d'impacts de leurs retombées, des modèles numériques sont utilisés en opérationnel et basés sur des paramètres éruptifs, regroupés sous la notion de terme source, caractérisant l'émission des panaches. L'ensemble du terme source est cependant difficile à mesurer en temps réel. C'est pourquoi les modèles de dispersion sont souvent basés sur des scénarios d'éruptions passées et utilisent des lois empiriques reliant la hauteur des panaches avec les flux massiques à la source. Cependant, les résultats qui découlent de ces modèles sont peu contraints, moyennés sur la durée des éruptions, et souffrent de larges incertitudes. Dans cette optique, les radars Doppler, capables de sonder l'intérieur des colonnes éruptives avec des échelles spatio-temporelles fines, peuvent fournir des contraintes cruciales sur le terme source des panaches en temps réel. Ce travail de thèse traite des applications de radars volcanologiques dédiés, potentiellement transposables aux radars météorologiques communément utilisés, afin de fournir des paramètres éruptifs à la source des panaches de téphras en surveillance opérationnelle mais également pour contraindre la dynamique des colonnes éruptives et les charges internes des panaches et de leurs retombées. Une campagne de mesures au volcan Stromboli a permis de montrer les capacités d'un couplage innovant entre un disdromètre optique (Parsivel2) avec un nouveau radar Doppler à onde millimétrique (Mini-BASTA). Grâce à l'excellente résolution spatio-temporelle de Mini-BASTA (12,5 m et 1 s), des figures intermittentes de sédimentation ont été observées dans les retombées de panaches transitoires dilués. Observées également au disdromètre mesurant la vitesse et la taille des retombées, ces figures ont été reproduites en laboratoire grâce à un modèle analogique. Un modèle conceptuel de formation de thermiques de sédimentation inversés est proposé pour expliquer ces figures et implique que les processus menant à une sédimentation irrégulière typique des panaches soutenus et concentrés peuvent s'appliquer à des panaches dilués, y compris ceux issus d'éruptions Stromboliennes normales en régime transitoire. Ensuite, une caractérisation physique d'un grand nombre de particules de cendres échantillonnées à Stromboli a permis de valider les mesures de tailles et de vitesses terminales de chutes par disdromètre sur le terrain et en laboratoire, justifiant par ailleurs son utilisation opérationnelle. A partir de ces contraintes, une loi reliant les concentrations de cendres avec les facteurs de réflectivité calculés a pu être comparée aux mesures radar in situ. Les concentrations internes modale et maximale des panaches de Stromboli sont respectivement autour de 1 × 10-5 kg m-3 et 7,45 × 10-4 kg m-3, largement supérieures au seuil fixé pour la sécurité aérienne. Les concentrations en cendres des retombées s’étalent entre 1,87 × 10-8 - 2,42 × 10-6 kg m-3 avec un mode vers 4 × 10-7 kg m-3.Finalement, ce travail de thèse montre les applications opérationnelles du radar UHF VOLDORAD 2B dans le cadre de la surveillance de l'activité de l'Etna. Une méthodologie, applicable à tout radar Doppler, a été développée pour obtenir des flux de masse de téphras en temps réel à partir d’un proxy de masse, uniquement basé sur les vitesses d'éjection et puissances mesurées, calibré avec un modèle de colonne tenant compte de l'influence du vent sur les panaches. La gamme de flux trouvée pour 47 paroxysmes entre 2011 et 2015 s’étend de 2.96 × 104 à 3.26 × 106 kg s-1. A partir d’un autre modèle de colonne éruptive, Plume-MoM, les flux radar ont permis de modéliser des hauteurs des panaches de téphras émis lors de quatre paroxysmes de l'Etna cohérentes avec les observations faites en temps réel par imagerie visible et par radar en bande-X. (...)
Volcanic tephra plumes are one of the major volcanic hazards. To forecast their dispersion and the impact zones of their fallout, the numerical models used in operational monitoring are based on eruptive parameters, called the source term, characterizing the plume emission. Source term parameters are challenging to measure in real time. This is why dispersion models are often based on past eruptive scenarios and use empirical laws that relate plume heights to source mass fluxes. However, the model outputs are not well constrained, averaged over the eruption duration, and suffer from large uncertainties. In this topic, Doppler radars are capable of probing the interior of eruptive columns and plumes at high space-time resolution and can provide crucial constraints on the source term in real time. This thesis deals with applications in operational monitoring of dedicated volcanological radars, potentially transposable to most common meteorological radars, to provide eruptive parameters at the source of tephra plumes but also to constrain the dynamics and internal mass load of eruptive columns, volcanic plumes and their fallout.A measurement campaign at Stromboli volcano has shown the capabilities of an innovative coupling between an optical disdrometer (Parsivel2) and a new 3-mm wave Doppler radar (Mini-BASTA). Owing to its high spatio-temporal resolution (12.5 m and 1 s), intermittent sedimentation patterns were observed in the fallout of dilute transient plumes typical of normal strombolian activity. These features, also recorded with the disdrometer, measuring the particle settling speeds and sizes, were reproduced in the laboratory using an analog model. A conceptual model for the formation of reversed sedimentation thermals is proposed to explain these features. It implies that processes leading to irregular sedimentation typical of sustained concentrated strong plumes can be applied to dilute weak plumes, including those formed by normal transient Strombolian activity. Then, a physical characterization of a large number of ash particles sampled at Stromboli allowed the validation of particle size and terminal velocity measurements by the disdrometer in the field and in the laboratory, arguing in favor of its operational use. Then, a physical characterization of a large number of ash particles sampled at Stromboli allowed to validate the measurements of size and terminal velocity of falls by disdrometer in the field and in laboratory, justifying also its operational use. From these constraints, a law relating ash concentrations with calculated reflectivity factors was found and compared to in situ radar measurements inside ash plumes and fallout. The modal and maximum internal concentrations of Strombolian plumes are at about 1 × 10-5 kg m-3 and 7.5 × 10-4 kg m-3 respectively, well above the threshold for aviation safety. Ash concentrations in the fallout range from 1.9× 10-8 to 2.4 × 10-6 kg m-3 with a mode at about 4 × 10-7 kg m-3.Finally, this thesis work shows operational applications of the UHF VOLDORAD 2B radar for the monitoring of explosive activity at Etna. A methodology, applicable to any Doppler radar, has been developed to obtain tephra mass eruption rates in real time from a mass proxy, based only on measured ejection velocities and power, and calibrated with an eruptive column model taking crosswinds into account. Tephra mass fluxes found for 47 paroxysms between 2011 and 2015 range from 3 × 104 to over 3 × 106 kg s-1. Then, tephra plumes heights of four Etna paroxysms were simulated using the eruptive column model Plume-MoM from the radar-derived mass eruption rates and were found consistent with real-time observations made by visible imagery and by X-band radar. This last part demonstrates the capabilities of VOLDORAD 2B to provide quantitative input parameters for dispersion models in the case of future Etna paroxysms. (...)

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
One of the challenges of modern agriculture is adapting to climatic effects, including the capability of rainfall events in causing erosion. Understanding the climatic phenomena depends on the monitoring of rain variables that express the magnitude and pattern of erosive agents. The kinetic energy of rain (E) and the maximum intensity of 30 minutes (I30) are key variables to represent the capability of rain in causing erosion, and the product of the two being one of the most known and used erosivity indices (EI30). However, in Brazil, to obtain direct and continuous measurements of E are incipient, as long series of rain intensity data (I) are scarce. Therefore, empirical equations based on rainfall information that are easy to acquire as daily or monthly accumulated rain (P) are used. The aim of this study is to analyze a set of data with hydrological variables, especially rainfall characteristics (volume, duration and energy) responsible for triggering the erosion process and its relationship with flow behavior (Q), suspended sediment concentration (SSC) and sediment yield (SY) in a rural catchment. From the analysis of the variables, E and EI30 estimation equations are proposed for the study site. The study was conducted in a 1.23 km² experimental catchment located in southern Brazil, where monitoring of the main hydrological flows (P, Q and SSC) has been carried out since 2002. P is monitored with pluviometers and rain gauges, and E has been measured since 2014 by a disdrometer (Parsivel2 - OTT). From this set of data, different equations for the estimation of E=f(I) and models for the estimation of EI30 were explored. Complementarily, a comparison was made between the equations obtained with equations available in the literature for the estimation of E and EI30. Additionally, this study also explored seasonal variations in rainfall characteristics (I30 P, E) and related them to Q, SSC and SY of the catchment in order to demonstrate the importance of E and I30 for the hydrossedimentological modeling. The measured E values were similar to the values estimated by the equations of Foster et al. (1981) and van Dijk et al. (2002), while Brown and Foster (1987) equation underestimate the values of E. EI30 was also quantified over a period of 8 years and an equation was proposed to estimate EI30 by accumulated daily rainfall variables. From 15 years of data, an annual EI30 value is presented and its average distribution between the 12 months of the year. The main results are: (a) a new equation for estimating E from the I measurement, its seasonal variability and similarities with equations previously known; (B) the relationship between measured E data and measured hydrological variables at catchment scale; (C) the EI30 factor for the Arvorezinha/RS region; (D) new indices for estimating EI30 from daily rainfall records.
Um dos desafios da agricultura moderna é a adaptação aos efeitos climáticos, dentre eles a capacidade dos eventos chuvosos em causar erosão. A compreensão dos fenômenos climáticos depende necessariamente do monitoramento das variáveis da chuva que expressarão a magnitude e o padrão dos agentes erosivos. A energia cinética da chuva (E) e a intensidade máxima de 30 minutos (I30) são variáveis fundamentais para representar a capacidade da chuva em causar erosão, sendo o produto das duas um dos índices de erosividade (EI30) mais conhecidos e utilizados. Entretanto, no Brasil, a obtenção de medidas diretas e contínuas da E são incipientes, assim como longas séries de dados de intensidade da chuva (I) são escassos. Por conta disso, são utilizadas equações empíricas baseadas em informações da chuva que são de fácil aquisição como chuva acumulada (P) diária ou mensal. O objetivo deste trabalho é analisar um conjunto de dados com variáveis hidrológicas, especialmente propriedades da chuva (volume, duração e energia) responsáveis pelo desencadeamento do processo de erosão hídrica, e sua relação com o comportamento da vazão (Q), concentração de sedimentos em suspensão (CSS) e produção de sedimentos (PS) em uma bacia hidrográfica rural. A partir da análise das variáveis são propostas equações de estimativa da E e EI30 para o local de estudo. O estudo foi conduzido em uma bacia hidrográfica experimental de 1.23 km², localizada no sul do Brasil onde é realizado o monitoramento dos principais fluxos hidrológicos (P, Q e CSS) desde 2002. A P é monitorada com pluviômetros e pluviógrafos, e a E tem sido medida desde 2014 por um disdrômetro (Parsivel2 – OTT). A partir desse conjunto de dados foram exploradas diferentes equações para a estimativa da E = f(I) e também modelos para a estimativa do EI30. Complementarmente, foi realizada uma comparação entre as equações obtidas com equações disponíveis na literatura para a estimativa da E e EI30. Além disso, esse estudo também explorou variações sazonais nas propriedades da chuva (I30, P, E) e as relacionou com a Q, CSS e PS da bacia na busca de demonstrar a importância da E e I30 para a modelagem hidrossedimentológica. Os valores de E medidos foram semelhantes aos valores estimados pelas equações de Foster et al. (1981) e van Dijk et al. (2002), ao passo que a equação de Brown e Foster (1987) subestima os valores de E. Também foi quantificado o EI30 em um período de 8 anos e proposto uma equação para estimativa do EI30 por variáveis de chuva acumulada na escala diária. A partir de 15 anos de dados é apresentado um valor de EI30 anual e sua distribuição média entre os 12 meses do ano. Os principais resultados encontrados são: (a) uma nova equação para estimativa da E a partir da I medida, sua variabilidade sazonal e semelhanças com equações conhecidas previamente; (b) a relação entre dados de E medida e variáveis hidrológicas medidas na escala de bacia hidrográfica; (c) o fator EI30 para a região de Arvorezinha/RS; (d) novos índices para estimativa do EI30 a partir de registros de chuva diários.

In questo lavoro di tesi si studiano quattro sistemi precipitanti di carattere principalmente convettivo che hanno interessato la regione Emilia-Romagna tra la primavera 2012 e l'inverno 2013. Si fornisce una trattazione che prevede l'utilizzo di due strumenti basati sulla tecnologia radar: il pluviometro disdrometro a microonde PLUDIX e il radar polarimetrico in banda C di San Pietro Capofiume (SPC). Gli strumenti sono posizionati ad una distanza di circa 30 km in linea d'aria. PLUDIX, situato al Consiglio Nazionale delle Ricerche (CNR) di Bologna, rileva le idrometeore al suolo e fornisce informazioni pluviometriche e disdrometriche sulla precipitazione in corso. Il radar SPC analizza echi provenienti dall'atmosfera circostante, fino alla distanza di 112.5 km e all'elevazione di 13° rispetto a terra. Si confrontano i profili temporali di intensità di precipitazione ottenuti da PLUDIX con quelli ricavati dalle variabili polarimetriche radar, che permettono di meglio interpretare l'evoluzione temporale degli eventi. Si procede, inoltre, alla classificazione delle idrometeore in atmosfera. A tal fine si implementa un algoritmo di classificazione polarimetrico basato sul lavoro di Park et al. (2009) e modificato in funzione della letteratura scientifica al riguardo. La classificazione di idrometeore che più interessa è quella relativa alle quote radar sulla verticale del CNR, che può essere messa a confronto con le evidenze disdrometriche da PLUDIX al suolo. I risultati sono soddisfacenti e mostrano che i due strumenti vedono gli stessi fenomeni da due punti di vista. L'analisi combinata dei dati eterogenei da PLUDIX e dal radar SPC permette di ricavare importanti informazioni sui processi fisici in nube e sull'evoluzione temporale e spaziale dei sistemi precipitanti.

碩士
國立清華大學
電機工程學系
104
In this sturdy, an image-based disdrometer has been developed. The system uses a CCD camera to capture falling raindrops and applies proper image processing techniques to determine the characteristics of raindrops. The observed data can be used to analyze raining condition and increase the accuracy of analyzing precipitation in small area. In the system, a telecentric lens is applied with the camera to reduce the blur effect and distortion from out of focus, which is easier to measure the shape more accurately. However, the telecentric lens needs enough illuminance to capture raindrops, so a light source is also applied. Due to the limitation of camera frame rate, it is difficult to measure the raindrop shape and velocity in one measurement. That is, two different exposure time measurements, 100us and 2000us, are applied to measure shape and velocity respectively. Furthermore, the details of image processing procedures are also introduced. Finally, three kinds of experiments were done to verify the system. Marble experiments verified the feasibility and performance of the system structure and image processing procedures. Water sprinkling experiments simulated the raining condition with more uncertainty than the marble experiment. Last, real raining condition pictures were taken and analyzed by the system. The analyzed data was compared with the data from Hsinchu weather station, Central Weather Bureau, Taiwan. An error rate of 14.42% in rain rate was obtained.

博士
國立中央大學
大氣物理研究所
98
The drop size distribution (DSD) and drop shape relation (DSR) characteristics observed by a ground based 2D-Video disdrometer and retrieved from the C-band polarimetric radar in the typhoon systems during landfall and on the ocean near the northern Taiwan in the Western Pacific regions were analyzed. The DSDs evolution and its relation with the vertical development of the reflectivity of two rain band cases were investigated. Three different types of precipitation system were studied: 1) weak stratiform type 2) stratiform type and 3) convective type according to characteristics of the mass-weighted diameter (Dm), the maximum diameter and the vertical structure of reflectivity. Further study of the relationship between the 15 dBZ contour height (H) of the vertical reflectivity profile, surface reflectivity (ZHH) and the mass-weighted diameter (Dm) showed that Dm increased with corresponding increase in the system depth (H) and reflectivity (ZHH). The analysis of DSDs retrieved from NCU C-band polarimetric radar measurements and disdrometer in typhoon concluded that the DSDs from the typhoon systems on the ocean were mainly maritime convective type. However, the DSDs collected over land tended to uniquely locate in between of the continental and maritime clusters. The ”effective DSR” of typhoon systems tends to be more spherical with drops greater than 1.5 mm when higher horizontal winds (maximum wind speed was less than 8 m sec-1). A detailed observing system simulation experiment (OSSE) was used for evaluating performance of the variational-based attenuation correction method and the ΦDP-based method. The variational-based method always estimates more accurate attenuation than the ΦDP-based method. The accuracy of attenuation-corrected X-band measurements in actual field measurements was evaluated by comparing the measurements with collocated NCAR S-band radar measurements. It was shown that the variational-based method is less sensitive to measurement noise in radar observations. Attenuation-corrected X-band radar measurements are also compared with disdrometer-based simulated ZHH and ZDR observations. There were instances, where large artifacts in ZDR (differential reflectivity) and ΦDP (differential phase shift) due to steep gradients in storm intensity, limited the usefulness of the variational-based method.

碩士
國立中央大學
太空科學研究所
102
The research is to record the rainfall phenomenon of TRAMI-typhoon.We can obtain precipitation terminal velocity, echo power, rain fall rate, DSD and the spectral width etc by using the Chung-Li 52MHz VHF radar and ground 2DVD- Disdrometer. The data is the events from August 20th 15:01~August 22th,2013.We can distinguish the cold precipitation events and the warm precipitation events with the air vertical velocity and bright band,and make scatter diagram by using the relation between precipitation terminal velocity and echo power in air to obtain the N_0 from exponential and gamma of DSD of precipitation particle and the N_0 from ground 2DVD- Disdrometer. The slope is closer to 1 and the correlation coefficient is very well,when only takes not only the cold precipitation events but the DSD is exponential. We take the time from August 20th 19:02:04 to 20:03:10 to make the scatter diagram of air echo power with the spectral width,and air echo power with the air vertical velocity,because we found the presence of the strong updraft, average Doppler velocity maximum nearly 15m/s on August 20 at about 19:42 near 8-10 km.Then we found the correlation coefficient ratio of the range 7.05km~12.3km is better than the range 1.65km~6.9km. We can use the filter criteria to distinguish the character between ice and supercooled above melting layer(5.4km) by terminal velocity greater than 2.5m/s.The average echo power between ice and supercooled water is 8-11dB,and supercooled water is greater than ice about 0.15Hz in average spectral width.We have lightning echo signals in this observing data.

碩士
國立臺灣大學
生物環境系統工程學研究所
104
The equation for evaluating rainfall kinetic energy currently used in Taiwan is not derived from the local rainfall data. Because rainfall kinetic energy is quite related to the region, it is necessary to develop an equation of rainfall kinetic energy for each area. The main purposes of this study are to measure the rain drop size distribution in northern Taiwan using disdrometer and to establish the equation for evaluating rainfall kinetic energy using the measured data. In this study, the data of rainfall and rain drop size distribution collected at three observation stations, namely, National Central University station, Xiayun station and Feitsui station, using disdrometer from 2012 to the Jun. of 2016 were used to evaluate the rainfall kinetic energy. To accomplish this, three methods for evaluating rainfall kinetic energy were applied. The first is the method of energy per unit volume (KEmm ), a conventional method, and its coefficient of determination( R2) between rainfall kinetic energy and rainfall intensity is approximately 0.6. The second is the method of energy per unit time (KEtime ), a relatively newly developed method, and the coefficient of determination( R2) between rainfall kinetic energy and rainfall intensity is greater than 0.97. The third is the method using attribute characteristics such as drop size distribution, precipitation types and the rainfall intensity to categorize the rainfall events and develop the KE-I relationship. While the rainfall is categorized with the drop size distribution (DSD), the KEmm remains constant over various rainfall intensities, and the results are very good. However, while the precipitation types and the rainfall intensity are used for categorizing, the results are not satisfactory. In this study, several methods are used to develop the equations for evaluating rainfall kinetic energy using the local rainfall data. Among these, the results of the KEtime method and the third method using the drop size distribution (DSD) to categorize the rainfall are much better. Accordingly, the findings in this study are expected to be useful for evaluating rainfall kinetic energy and rainfall erosion index in the future.

碩士
國立中央大學
大氣物理研究所
97
In this study, we used the wind profiler and 2D-Video disdrometer (2DVD) to observed different precipitating system during the Southwest Monsoon Experiment (SoWMEX/TiMREX). At first, we use three classification methods to classify precipitation type and basically we can get the same characteristics of different type of precipitation, no matter what method is used. When we used the classification algorithms from 2DVD, we could find that, the ratio of straitiform precipitation time is about 90%. However, the ratio of convective precipitation time is about 10%. And then we used the wind profiler to classify precipitating clouds into either stratiform, mixed stratiform/convective, deep convective, or shallow convective clouds by analyzing the vertical structure of Doppler vertical velocity and spectral width. If the mixed stratiform/convective classification and the convective classification are combined into one type, then we can also get similar result, the ratio of precipitation time is about 90%, and the convective precipitation time is about 90%. Using wind profiler to classify different precipitating system into either strati- form, mixed stratiform/convective, deep convective, or shallow convective clouds during the SoWMEX/TiMREX experiment, we can find that, the vertical velocity of stratiform precipitation of Mei-Yu front is greater than MCS about 1 m/s. But the vertical velocity of convective precipitation of Mei-Yu front is smaller than MCSs about 1 m/s. The CFADS (Contoured Frequency by Altitude Diagrams) of reflectivity and vertical velocity of mixed and stratiform types, it shows a distinct bright band and associated large vertical gradient in Doppler velocity at the altitude of 4~5 km. But for the convective rain, no bright band was found. The spectral width frequency distribution for the stratiform precipitating system shaws narrow distribution above melting layer. However, mixed type precipitating system had broad distribution of spectral widths above melting layer, this means turbulent motions are possibly occurring within the cloud. However the spectral width frequency distribution for the convective precipitating system, the shape is different from above. It appears narrow in the lower layer, but broad in the higher layer of atmosphere. At the same time, the observational results of 2DVD of Mei-Yu and MCS, when rainfall rate smaller than 50 mm/hr, will greater with rainfall rate. But when rainfall rate greater than 50 mm/hr, seems stop growing at the value 2.1, it shows drop size has some limitation. When rainfall rate is small, log10( ) is scattered. When rainfall rate greater, log10( ) will also larger. It seems the log10( ) and rainfall rate is much closed related in larger rainfall rate. The relationship between μ、Λ and rainfall rate, when rainfall rate smaller than 10 mm/hr, μ、Λ is scattered and broad. But when rainfall rate is greater, μ、Λ will also become smaller. From the μ、Λ scatter plot, we can see that μ、Λ has positive correlation. For the afternoon thundershowers, we also can see that when rainfall rate smaller than 10 mm/hr, μ、Λ are scattered and broad, and μ、Λ has positive correlation. For the rainfall of mixed and convective type, the average of drop size distribution of MCS is larger and greater than Mei-Yu front case. However there is no big DSD difference for stratiform type between Mei-Yu front and MCS, but Mei-yu front case has more big rain drop. For the afternoon thundershowers, the average of drop size distribution is the most narrow and N(D) is the smallest, the result may be due to the afternoon thundershowers systems already dissipated when they moved over the wind profiler and 2DVD site.

Storms in the SE-US often evolve in different environments than those in the central Plains. Many poorly understood aspects of these differing environments may impact the tornadic potential of SE-US storms. Among these differences are potential variations in the CCN concentration owing to differences in land cover, combustion, industrial and urban activity, and proximity to maritime environments. The relative influence of warm and cold rain processes is sensitive to CCN concentration, with higher CCN concentrations producing smaller cloud droplets and more efficient cold rain processes. Cold rain processes result in DSDs with relatively larger drops from melting ice compared to warm rain processes. Differences in DSDs impact cold pool and downdraft size and strength, that influence tornado potential. This study investigates the impact of CCN concentration on DSDs in the SE-US by comparing DSDs from ARPS-EnKF model analyses and forecasts to observed DSDs from portable disdrometer-equipped probes collected by a collaboration between Purdue University, the University of Oklahoma (OU), the National Severe Storms Laboratory (NSSL), and the University of Massachusetts in a tornadic QLCS on 30 April 2017 during VORTEX-SE.

The ARPS-EnKF configuration, which consists of 40 ensemble members, is used with the NSSL triple-moment microphysics scheme. Surface and radar observations are both assimilated. Data assimilation experiments with CCN concentrations ranging from 100 cm^-3 (maritime) to 2,000 cm^-3 (continental) are conducted to characterize the variability of DSDs and the model output DSDs are verified against the disdrometer observations. The sensitivity of the DSD variability to CCN concentrations is evaluated. Results indicate continental CCN concentrations (close to CCN 1,000 cm³) produce DSDs that align closest to the observed DSDs. Other thermodynamic variables also accord better to observations in intermediate CCN concentration environments.

Natural phenomena such as rainfall are responsible for communication service disruption, leading to severe outages and bandwidth inefficiency in both terrestrial and satellite systems, especially above 10 GHz. Rainfall attenuation is a source of concern to radio engineers in link budgeting and is primarily related to the rainfall mechanism of absorption and scattering of millimetric signal energy. Therefore, the study of rainfall microstructure can serve as a veritable means of optimizing network parameters for the design and deployment of millimetric and microwave links. Rainfall rate and rainfall drop-size are two microstructural parameters essential for the appropriate estimation of local rainfall attenuation. There are several existing analytical and empirical models for the prediction of rainfall attenuation and their performances largely depend on regional and climatic characteristics of interest. In this study, the thrust is to establish the most appropriate models in South African areas for rainfall rate and rainfall drop-size. Statistical analysis is derived from disdrometer measurements sampled at one-minute interval over a period of two years in Durban, a subtropical site in South Africa. The measurements are further categorized according to temporal rainfall regimes: drizzle, widespread, shower and thunderstorm. The analysis is modified to develop statistical and empirical models for rainfall rate using gamma, lognormal, Moupfouma and other ITU-R compliant models for the control site. Additionally, rain drop-size distribution (DSD) parameters are developed from the modified gamma, lognormal, negative exponential and Weibull models. The spherical droplet assumption is used to estimate the scattering parameters for frequencies between 2 GHz and 1000 GHz using the disdrometer diameter ranges. The resulting proposed DSD models are used, alongside the scattering parameters, for the prediction and estimation of rainfall attenuation. Finally, the study employs correlation and regression techniques to extend the results to other locations in South Africa. The cumulative density function analysis of rainfall parameters is applied for the selected locations to obtain their equivalent models for rainfall rate and rainfall DSD required for the estimation of rainfall attenuation.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.