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Die mittlere Windgeschwindigkeit kann aus den Komponenten der Geschwindigkeit (Vektorwind) und aus dem Windweg eines Schalensternanemometers (Skalarwind) berechnet werden. Diese beiden Geschwindigkeiten werden verglichen, indem große Datensätze von Windmeßreihen hoher Auflösung, die mittels Ultraschallanemometer gewonnen wurden, benutzt werden. Der Skalarwind ist verursacht durch die Turbulenz immer größer als der Vektorwind, die Abweichungen betrugen bis zu 4%. Durch Benutzen von Normalverteilungen für die Komponenten des Windes wird eine analytische Lösung für diesen systematischen Fehler angegeben. Windmessungen mit einem Schalensternanemometer zeigen einen zweiten systematischen Fehler, das sogenannte Overspeeding. Dieses Verhalten wird durch ein einfaches Modell beschrieben. / Mean wind velocity can be calculated from the components of velocity (vector wind) and the wind way of a cup anemometer (scalar wind). The wind velocities resulting from different definitions of mean wind velocities are compared by using large dataset of fast-response wind measurements with an ultrasonic anemometer. It is found that the scalar wind is always greater then the vector wind up to 4% owing to the turbulence. Using Gaussian normal distribution for the components of wind velocity, an analytical solution is given for this systematic error. Wind velocity measured with cup anemometer shows second systematic error called overspeeding which is described by a simple mathematical model.

Detaljerad information om vindförhållandena på en site är en nödvändighet för att göra beräkningar av lönsamhet i ett vindkraftsprojekt. Mätningarna behöver vara kontinuerliga och så korrekta som möjligt. Därtill bör de göras under minst ett års tid eftersom vindförhållandena på en plats är säsongsberoende. Under vintertid och framför allt på högre latituder eller altituder, kan mätutrustning påverkas av nedisning. En nedisad anemometer kan ge databortfall eller felaktiga mätningar. Identifiering av felaktiga data är en viktig del av analyseringsarbetet eftersom risken annars är att vindförhållandena på platsen underskattas. Då instrumentet är helt fastfruset kan en enklare analys av data göras genom att titta på standardavvikelsen av vindhastigheten. Svårigheten i detektionen är vid lätt till måttlig nedisning då vindstyrkan, och även standardavvikelsen, kan se normal ut trots att felaktiga värden redovisats. I detta arbete analyseras 1 Hz data från skålkorsanemometer för att söka ett matematiskt sätt att avgöra om lätt till måttlig nedisning påverkat instrumentet under mätperioden. I ett experiment har olika typer av nedisning simulerats på skålkorsanemometrar. Därefter har vindhastighetsfördelningen för en ”nedisad” anemometer kunnat jämföras med fördelningen uppmätt med en anemometer som varit opåverkad under samma mätperiod. I denna jämförelse har visats att trots en differens i medelvind-hastighet på upp till 15 % under mätperioden syns ingen, för detektion av nedisning, användbar skillnad i någon av de statistiska parametrar som jämförts i arbetet. Förutom analys av mätdata från egna experiment har även data från Suorva samt från en höghöjdsmast i Norrland analyserats. För analys av mätdata från masten i Norrland har ett en algoritm utarbetats för automatisk detektion av tidpunkter med instrumentell nedisning. Isdetektionen baseras på antaganden om standardavvikelse av vindhastighet och vindriktning, förändring av vindriktning samt en regression mellan vindhastigheten på två höjder. / Detailed information about the wind conditions on a site is a necessity for calculations of profitability from a wind power project. Hence the continuity and the correctitude of the measurements are crucial when making the site evaluations. Due to the season dependence of the wind conditions the measurements also needs to be done for at least a whole year. During wintertime and particularly on higher altitudes and/or latitudes the instruments may be affected by icing. An iced up anemometer often underestimates the wind speed and severe icing can lead to instrument breakage and loss of data. Identification of inaccurate measurements is of great importance in the analysis of the site’s energy potential. The difficulty in detecting light to moderate icing lies in that the wind speed and the standard deviation of the wind may seem normal, although the anemometer is underestimating the wind speed due to icing. In this thesis 1 Hz data from cup anemometers are analysed in search for a mathematical way to determine whether the instrument has been affected by icing during the measurement. An experiment has been performed simulating different types of icing on anemometers. The wind velocity distribution of an “iced up” anemometer has been compared to the wind velocity distribution of an unaffected anemometer for the same measuring period. Also the turbulence intensity and the change of mean wind velocity between observations have been evaluated. The comparison of these statistical variables between the instruments has showed that none of them are applicable for detection of icing. In addition to analysing data from the experiment a pre-study on the subject has been made analysing measurements with possible icing from the Suorva valley. Also, the results from the experiment have been compared to results from a conventional measuring mast placed in the northern part of Sweden. For the analysis of the mast data an algorithm for detection of icing during measurements has been implemented. This automatic detection of icing is based on assumptions about the standard deviation of wind speed, the standard deviation of the wind direction, the change of wind direction and regression between wind velocities of two heights.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / The Delay Mapping Receiver (DMR) is used for receiving and processing the reflected GPS signal to get the information of sea surface wind by recording and matching the data with the theoretical model. The hardware architecture and software design are described in detail in this paper. The test results at near sea of Tianjin of China are provided, which prove that the design of DMR is successful and the collected data are useful for the sea surface wind measurement.

Variable-rate technologies for sprayer applications stand to increase efficacy by ensuring the right amount of chemical is applied at the right location. However, external environmental factors such as droplet drift caused by variable ambient condition, are not yet integrated into modern sprayer systems. Real-time wind velocity measurements can be used to control droplet spectra for reducing spray drift by actuating a variable-orifice nozzle. This work aimed to develop data processing methods needed to filter noise and remove vehicle speed from wind velocity measurements collected with an ultrasonic anemometer aboard a moving platform. Using a global navigation satellite system (GNSS), vehicle speed was calculated in the field and subtracted from apparent wind velocity for comparison to static measurements. Experiments under stationary and dynamic sensor deployments were used to develop an algorithm to provide instantaneous local wind velocity and to better understand the local spatiotemporal variability of wind under field conditions.

Die mittlere Windgeschwindigkeit kann aus den Komponenten der Geschwindigkeit (Vektorwind) und aus dem Windweg eines Schalensternanemometers (Skalarwind) berechnet werden. Diese beiden Geschwindigkeiten werden verglichen, indem große Datensätze von Windmeßreihen hoher Auflösung, die mittels Ultraschallanemometer gewonnen wurden, benutzt werden. Der Skalarwind ist verursacht durch die Turbulenz immer größer als der Vektorwind, die Abweichungen betrugen bis zu 4%. Durch Benutzen von Normalverteilungen für die Komponenten des Windes wird eine analytische Lösung für diesen systematischen Fehler angegeben. Windmessungen mit einem Schalensternanemometer zeigen einen zweiten systematischen Fehler, das sogenannte Overspeeding. Dieses Verhalten wird durch ein einfaches Modell beschrieben. / Mean wind velocity can be calculated from the components of velocity (vector wind) and the wind way of a cup anemometer (scalar wind). The wind velocities resulting from different definitions of mean wind velocities are compared by using large dataset of fast-response wind measurements with an ultrasonic anemometer. It is found that the scalar wind is always greater then the vector wind up to 4% owing to the turbulence. Using Gaussian normal distribution for the components of wind velocity, an analytical solution is given for this systematic error. Wind velocity measured with cup anemometer shows second systematic error called overspeeding which is described by a simple mathematical model.

The theory of Lagrangian Coherent Structures (LCS) enables prediction of material transport by turbulent winds, such as those observed in the Earth's Atmospheric Boundary Layer. In this dissertation, both theory and experimental methods are developed for utilizing small fixed-wing unmanned aircraft systems (UAS) in detecting these atmospheric coherent structures. The dissertation begins by presenting relevant literature on both LCS and airborne wind estimation. Because model-based wind estimation inherently depends on high quality models, a Flight Dynamic Model (FDM) suitable for a small fixed-wing aircraft in turbulent wind is derived in detail. In this presentation, some new theoretical concepts are introduced concerning the proper treatment of spatial wind gradients, and a critical review of existing theories is presented. To enable model-based wind estimation experiments, an experimental approach is detailed for identifying a FDM for a small UAS by combining existing computational aerodynamic and data-driven approaches. Additionally, a methodology for determining wind estimation error directly resulting from dynamic modeling choices is presented and demonstrated. Next, some model-based wind estimation results are presented utilizing the experimentally identified FDM, accompanied by a discussion of model fidelity concerns and other experimental issues. Finally, an algorithm for detecting LCS from a single circling fixed-wing UAS is developed and demonstrated in an Observing System Simulation Experiment. The dissertation concludes by summarizing these contributions and recommending future paths for continuing research. / Doctor of Philosophy / In a natural or man-made disaster, first responders depend on accurate predictions of where the wind might carry hazardous material. A mathematical theory of Lagrangian Coherent Structures (LCS) has shown promise in ocean environments to improve these predictions, and the theory is also applicable to atmospheric flows near the Earth’s surface. This dissertation presents both theoretical and experimental research efforts towards employing small fixed-wing unmanned aircraft systems (UAS) to detect coherent structures in the Atmospheric Boundary Layer (ABL). These UAS fit several “gaps” in available sensing technology: a small aircraft responds significantly to wind gusts, can be steered to regions of interest, and can be flown in dangerous environments without risking the pilot’s safety. A key focus of this dissertation is to improve the quality of airborne wind measurements provided by inexpensive UAS, specifically by leveraging mathematical models of the aircraft. The dissertation opens by presenting the motivation for this research and existing literature on the topics. Next, a detailed derivation of a suitable Flight Dynamic Model (FDM) for a fixed-wing aircraft in a turbulent wind field is presented. Special attention is paid to the theories for including aerodynamic effects of flying in non-uniform winds. In preparation for wind measurement experiments, a practical method for obtaining better quality FDMs is presented which combines theoretically based and data-driven approaches. A study into the wind-measurement error incurred solely by mathematical modeling is presented, focusing on simplified forms of the FDM which are common in aerospace engineering. Wind estimates which utilize our best available model are presented, accompanied by discussions of the model accuracy and additional wind measurement concerns. A method is developed to detect coherent structures from a circling UAS which is providing wind information, presumably via accurate model based estimation. The dissertation concludes by discussing these conclusions and directions for future research which have been identified during these pursuits.

As wind energy plants continue to grow in size and complexity, advanced measurement technologies such as scanning Doppler LiDAR are essential for assessing site conditions and prospecting new development areas.   The RUNE project was initiated to determine best practices for the use of scanning LiDARs in resource assessments for near shore wind farms. The purpose of this thesis is to determine the optimum configuration for the plan position indicator (PPI) scan type of a scanning LiDAR. A task specific Automated Analysis Software (AAS) is created, and the sensitivity of the integrated velocity azimuth process (iVAP) reconstruction algorithm is examined using sector sizes ranging from 4 to 60 degrees. Further, a comparison to simultaneous dual Doppler measurement is presented in order to determine the necessity of deploying two LiDARs rather than one.    DTU has developed a coordinated long range coherent scanning multi-LiDAR array (the WindScanner system) based on modified Leosphere WindCube 200S devices and an application specific software framework and communication protocol. The long range WindScanner system was deployed at DTU’s test station in Høvsøre, Denmark and measurement data was collected over a period of 7 days. One WindScanner was performing 60 degree sector scans, while two others were placed in staring dual Doppler mode. All three beams were configured to converge atop a 116.5m instrumented meteorological mast.   A significant result was discovered which indicates that the accuracy of the reconstructed measurements do not differ significantly between sector sizes of 30 and 60 degrees. Using the smallest sector size which does not introduce systematic error has numerous benefits including: increasing the scan speed, measurement distance and angular resolution.   When comparing collocated dual Doppler, sector scan and in-situ met-mast instrumentation, we find very good agreement between all techniques. Dual Doppler is able to measure wind speeds within 0.1%, and 60 degree sector scan within 0.2% on average of the reference values. For retrieval of wind direction, the sector scan approach performs particularly well. This is likely attributable to lower errors introduced by the assumption of flow field homogeneity over the scanned area, in contract to wind direction which tends to be more non-uniform. For applications such as site resource assessments, where generally accurate 10 minute wind speed and direction values are required, a scanning LiDAR performing PPI scans with a sector size of between 30 and 38 degrees is recommended. The laser’s line of sight path should be directed parallel to the predominant wind direction and at the lowest elevation angle possible. / RUNE

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Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Tropical cyclones are synoptic scale rotating storms capable of generating intense wind speeds and rainfall with potentially devastating social and economic consequences. In addition to abnormally high winds and rainfall, the associated storm surge and extreme waves can lead to severe coastal erosion, damage to coastal property and inundation. A good understanding of the risk exposure to these events is therefore of great importance to planners and designers of coastal infrastructure in vulnerable regions. Probabilistic approaches have been routinely adopted for the calculation of extreme tropical cyclone induced wind speeds, with significant developments in these techniques over the last few decades. While the application of these approaches has become widely adopted in regions such as the North Atlantic, North Pacific and South Pacific Oceans, relatively little attention has been paid to the South-West Indian Ocean. This thesis focusses on the quantification of the risk exposure to tropical cyclones over the South-West Indian Ocean, using current state-of-the-art techniques. The primary results of the thesis are extreme wind speed maps at various return periods of interest for engineering design. Best track data for the South-West Indian Ocean, as archived by the Joint Typhoon Warning Centre (JTWC), has been used as the primary dataset forming the basis of this study. These data provide estimates of the location and intensity of historical tropical cyclones at six hourly intervals. Location data are provided as estimates of longitude and latitude of the eye, while intensity data are provided as estimates of the maximum sustained surface (10 m elevation) wind speed and/or minimum central pressure. The modelling of tropical cyclone wind fields has been carried out using both the Holland (1980) and the Willoughby et al. (2006) parametric wind field models. Using the limited information available in the best track data as input to the model, surface wind fields which reasonably resemble those of actual storms have been generated. Both considered parametric wind field models have been shown to yield reasonable wind speeds and directions when compared with measurements. Of the two considered models the Willoughby et al. (2006) model has been shown to provide the best fit to historical wind speed measurements. Extreme value analyses of tropical cyclone induced wind speeds based on historical data alone have been shown to lead to potentially large errors, owing to the small sample size of the historical data. This highlights the need to augment the historical database through a probabilistic approach. Largely following the methods described in Powel et al. (2005) and Emanuel et al. (2006), a synthetic track model for the South-West Indian Ocean has been developed. The objective of the synthetic track model is to simulate thousands of years of tropical cyclone tracks, thereby circumventing errors induced by small sample sizes in the available historical best track data. The synthetic track model developed as part of this study is a Markov chain model, capable of simulating track propagation and intensity evolution along the track, from track genesis through to termination. The model is purely statistical, based on properties derived from the historical best track data. Adjustments have however been made to account for physical limitations such as those imposed by the equator and the maximum potential intensity which an event can attain. The statistical characteristics of synthetic tracks have been shown to agree well with those of the historical population. Applying the Willoughby et al. (2006) wind field model along synthetic tracks has enabled the simulation of 5 000 years of tropical cyclone induced wind speeds at any location of interest in the South-West Indian Ocean. Applying calculations on a 1 degree geographical grid, wind speed maps corresponding to return periods of 50, 100, 200 and 500 years have been generated for the South-West Indian Ocean. Extreme wind speeds along coastal regions provide valuable input for the design of coastal infrastructure in the region. / AFRIKAANSE OPSOMMING: Tropiese siklone is sinoptiese orde roterende storms wat in staat is om aansienlike windspoed en reënval, tot gevolg te hê met potensiële vernietigende sosiale en ekonomiese gevolge. Benewens die abnormale sterk winde en hoë reënval kan die verwante stormdeinings en vloedgolwe lei tot ernstige kus-erosie, skade aan kusfront-eiendom en oorstromings. ‘n Goeie begrip van die risiko-blootstelling aan hierdie gebeurtenisse is daarom van groot belang vir die beplanners en ontwerpers van kus-infrastruktuur in kwesbare gebiede. As gevolg van die beduidende ontwikkeling van probabilistiese benadering tot die berekening van windspoed wat veroorsaak word deur ekstreme tropiese siklone, word hierdie tegnieke huidiglike op ‘n roetine basis aangewend. Terwyl die toepassing van hierdie benaderings wyd aanvaar word in gebiede soos die Noord-Atlantiese, Noordelike- en Suidelike Stille Oseaan, word relatief min aandag gegee aan die Suid-Westelike Indiese Oseaan. Hierdie tesis fokus op die kwantifisering van die risiko-blootstelling aan tropiese siklone in die Suid-Westelike Indiese Oseaan met die gebruik van die huidige gevorderdste tegnieke. Die primêre resultaat van die tesis is uiterste wind spoed kaarte vir ‘n verskeindenheid herhaal periodes wat van belang in vir engenieursontwerp. Beste roete-ata vir die Suid-Westelike Indiese Oseaan, soos voorsien deur die Gesametlike Tifoon Waarskuwing Sentrum (JTWC), is gebruik as die primêre data stel wat die basis vorm van hierdie studie. Hierdie data gee die beste skattings van die ligging (lengte- en breedtegraad), en intensiteit (maksimum volgehoue oppervlak (10m hoogte) wind spoed en/of sentrale druk tekort) van historiese tropiese siklone teen ses-uurlikse intervalle. Die modelering van tropiese sikloon windvelde was uitgevoer met die gebruik van die Holland (1980) en die Willoughby et al. (2006) parametriese windveldmodelle. Met die gebruik van beperkte inligting wat beskikbaar is in die beste roete data as invoer vir die model, was oppervlak wind velde gegenereer wat ‘n billike ooreenstemming het met die van werklike storms. Beide tegnieke se parametriese windveldmodelle is al bewys om redelike akkurate windspoed en windrigtings te lewer in vergelyking met waargenome waardes. Van die twee modelle het die Willoughby et al. (2006) model se resultate die beste ooreenstemming gewys met historiese wind spoed metings. Dit is al uitgewys dat uiterste waarde-analises van tropiese sikloon veroorsaakte windspoed moontlik kan lei tot groot foute in die resultate as gevolg van die klein monster-grootte van die historiese data. Dit beklemtoon die noodsaaklikheid om die historiese databasis aan te vul met behulp van probabilistiese metodes. Die metodes soos beskryf deur Powel et al. (2005) en Emanuel et al. (2006) is hoofsaaklik gebruik om ‘n sintetiese roete-model vir die Suid-Westelike Oseaan te ontwikkel. Die doelwit van die sintetiese roete model is om duisende jare se tropiese sikloonroetes te produseer, en in effek foute te vermy as gevolg van die gebruik van klein monster groottes van die beskikbare historiese beste roete data. Die sintetiese roete model wat tydens hierdie studie ontwikkel is, is ‘n Markov kettingmodel wat in staat is om die roete verspreiding asook die evolusie van intensiteit saam die roete te simuleer vanaf die onstaan tot die beëindiging van die sikloon se roete. Die model is suiwer statisties en is gebasseer op die eienskappe soos afgelei vanaf die historiese beste roete data. Aanpassings is gemaak om rekening te hou van die fisiese beperkings soos die wat opgelê word deur die ewenaar en die maksimum potensiële intensiteit wat ‘n sikloon kan bereik. Dit is voorgelê dat die statistiese einskappe van die sintetiese roetes goed saamstem met die van die historiese populasie. Die toepassing van die Willoughby et al. (2006) wind veld model langs die sintetiese roetes het dit moontlik gemaak om 5000 jaar se windspoed, wat veroorsaak is deur tropiese siklone, te genereer by enige ligging wat van belang is in die Suid-Westelike Indiese Oseaan. Met berekeninge wat op ‘n 1 grade geografiese ruitnet gedoen is, is windspoedkaarte vir herhaal periodes van 50, 100, 200 en 500 jaar opgestel vir die Suid-Westelike Indiese Oseaan. Die uiterste wind spoed in kusgebiede gee waardevolle invoer vir die ontwerp van kus-infrastruktuur in die omgewing.