Dissertations / Theses on the topic 'Aviation Meteorology'

In the atmosphere vertical extended layers that are in the state of super saturation with respect to ice can appear; these layers have been termed ice-supersaturated layers (ISSL). If an aircraft passes through an ISSL, persistent condensation trails can form. These contrails absorb the long wave radiation from the earth and reflect the incoming short wave radiation from space. The absorbing effect of the long wave radiation is although greater than the reflecting effect of the short wave radiation and therefore these contrails increase the greenhouse effect.This study contain statistics of when ice-supersaturated layers occur in the Swedish airspace, based on data from balloon soundings that take place each day at four locations in Sweden. The soundings that are used in this report were carried out from January 2006 to December of 2010. The results show that ISSL are more common in the Swedish airspace than expected. The layers are by average 42 hPa thick, located at the height of 339 hPa and are present in 44 % of the soundings.
I atmosfären kan det uppkomma vertikalt utsträckta skikt som är övermättade med avseende på is; dessa lager har blivit benämnda som ice-supersaturated layers (ISSL). Om ett flygplan flyger igenom dessa ISSL luftmassor kan permanenta kondensationsstrimmor bildas.Dessa kondensationsstrimmor absorberar den långvågiga strålningen från jorden och reflekterar den inkommande kortvågiga strålningen från rymden. Den absorberande effekten är större än den reflekterande effekten, vilket bidrar till en förstärkning av växthuseffekten. Den här studien innehåller statistik för när dessa ISSL uppkommer i det Svenska luftrummet, baserat på data från ballongsonderingar som var utförda från Januari 2006 till December 2010. Resultatet från denna statistik visar att ISSL är mer vanliga i det Svenska luftrummet än förväntat. Lagren är i medeltal 42 hPa tjocka, placerade på 339 hPa höjd och förekommer i 44 % av sonderingarna.

Thesis (Ph.D. in Philosophy (Marine, Earth, and Atmospheric Sciences))--North Carolina State University, July 2008.
Title from reproduction cover. "July 2008." Thesis advisor(s): S. Pal Arya and Michael L. Kaplan. Performed by North Carolina State University; sponsored by the United States Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio. Includes vita. "A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy, Marine, Earth, and Atmospheric Sciences from North Carolina State University. 2008."--P. [iv1]. "This research was funded by Air Force grant FA8718-04-C-0011."--p. ii. "Cl09-0007." Includes bibliographical references (p. 175-181). Also available online from the North Carolina State University Library and DTIC Online Web sites.

Aviation contributes significantly to anthropogenic climate change, and one promising possibility for mitigation is eco-efficient flight planning by avoiding climate sensitive regions with only small changes in the aircraft trajectories. Climate sensitive regions result from strong spatial variation of the global climate impact of local non-CO2 emissions, which are expressed by so-called climate change functions. Previous research established high-fidelity climate change functions (CCFs) for aviation water vapour and NOx emissions, and contrail formation with a climate model as inputs for air traffic optimisation. The mitigation potential in this case study is promising but the climate change function simulations are too computationally intensive for real-time calculation and thus cannot be applied operationally. In this study we show for the first time that this problem can be overcome by formulating algorithmic approximations of the global climate impact. Here we approximate water vapour concentration changes from local aviation water vapour emissions, ozone changes from local NOx emissions and methane changes from local NOx emissions (i.e. algorithmic climate change functions; aCCFs) from instantaneous model weather data using regression analysis. Four candidate algorithms are formulated per chemical species and traded off. The final adjusted regression coefficients, indicating how well the aCCFs represent the CCFs, are 0.59, 0.42, and 0.17 for water vapour, ozone and methane. The results show that the meteorology at the time of emission largely controls the fate of the emitted species, where the quality of the aCCF degrades with increasing lifetime of the respective species.

As a complement to existing weather forecast products for aviation, a prototype of a new product is presented and evaluated. It shows the atmosphere in a vertical cross section along the intended route. This Vertical Route Forecast introduces the possibility to examine the vertical distribution of cloud layers, wind, precipitation, turbulence and more along the flight path. Through a market research with 166 participating Swedish pilots it was found that the demand for the product is high and that 90 % of the participants would use it if available. The Vertical Route Forecast is inspired by the existing product GRAMET by Ogimet (Ballester Valor, n.d) but instead of using forecasts from the weather prediction model GFS (Global Forecast System) at 0.5° (56 km) resolution it uses data from the 2.5 km resolution model HARMONIE-AROME. The latter is operational at SMHI (Swedish Meteor-ological and Hydrological Institute) and because of its high resolution it enables more detailed structures of the weather to be presented. The product differs further from GRAMET by showing only the lower parts of the atmosphere so as to be of more use to small aircraft pilots flying at low levels. To assess the accuracy of the forecasts, a model evaluation of HARMONIE-AROME has been conducted through a case study in which the model was verified and compared to GFS over Sweden. The two models were verified against their own analyses at four different atmospheric pressure levels in terms of bias, root mean square error, standard deviation and correlation. HARMONIE-AROME performed best for temperature while GFS had the best forecasts of relative humidity. Wind speed and direction were also evaluated with insignificantly better results for GFS. However, the weather did not vary very much during the study as the two weeks were dominated by high pressure systems. Other evaluations made of HARMONIE-AROME by e.g. the HIRLAM consortium (2016a) have shown good or adequate performance of the model. It was concluded that HARMONIE-AROME would be well suited as the forecast producing model for this Vertical Route Forecast.
För att piloter ska kunna planera en säker flygning behöver de tillgång till bra och användbara väderprognoser. Med de prognosprodukter som finns tillgängliga idag kan det dock vara svårt att få en detaljerad uppfattning om hur vädret kommer vara längs med vägen. Här presenteras och utvärderas därför ett förslag till en ny prognosprodukt som visar atmosfären i en sidovy längs en valfri sträcka. Med den kan piloten granska utbredningen av bland annat molntäcken, vind, nederbörd och turbulens i höjdled längs den planerade färdvägen. Denna vertikala ruttprognos är inspirerad av den redan befintliga produkten GRAMET från Ogimet (Ballester Valor, n.d) men visar mer detaljerade prognoser som är bättre anpassade till flygningar på låga höjder. Vid en marknadsundersökning utförd med 166 medverkande svenska piloter stod det klart att efterfrågan på produkten är hög och 90 % av de medverkande påstod att de skulle använda den om den fanns tillgänglig. För att bedöma prognosernas precision har en utvärdering gjorts av den prognosmodell som använts till produkten. Modellen används annars hos SMHI (Sveriges Meteorologiska och Hydrologiska Institut) och kallas HARMONIE-AROME. I en fallstudie jämfördes den med modellen GFS som skapar prognoserna för GRAMET. Studien täckte Sverige och sträckte sig över 14 dagar i början av februari, 2017. HARMONIE-AROME visade bäst resultat för temperatur medan GFS gjorde de bästa fuktighetsprognoserna. Vindhastighet och vindriktning undersöktes också och för dem var modellerna ungefär lika bra. Vädret varierade dock inte så mycket under tvåveckorsperioden som dominerades av högtryck. Andra utvärderingar som gjorts av HARMONIE-AROME togs också i beaktande och modellen verkar generellt sett göra bra prognoser. Från samtliga resultat drogs slutsatsen att prognos-produkten skulle underlätta för småplanspiloter samt att HARMONIE-AROME är en lämplig modell att använda för att skapa dess prognoser.

This thesis is about wind shear and its influence on aviation. There is wide theoretical description of wind shear and it’s implemented into aviation practice. There are also methods of observation, forecasting and reporting, for both pilots and meteorologist described. In this thesis, pilots can find useful recommendations for dealing with wind shear during the flight. Every reader can also read about famous aviation accidents and look at models of weather that caused those accidents. At the end of thesis there are analyses of a rawiosonde measurements related to wind shear reports. This whole thesis is focused on increasing awareness of wind shear in aviation from angle of view of both pilots and aviation meteorologist.

Currently, the South Pole has a large data problem. It is estimated that 1.2 TB of data is being produced every day, but less than 500 GB of that data is being uploaded via aging satellites to researchers in other parts of the world. This requires those at the South Pole to analyze the data and carefully select the parts to send, possibly missing out on vital scientific information. The South Pole Carrier Pigeon will look to bridge this data gap. The Carrier Pigeon will be a small unmanned aerial vehicle that will carry a 30 TB solid-state hard drive from the South Pole to various destinations in the Southern Hemisphere, but it has been designed to y to Christchurch, New Zealand. This 87 lb. UAV will be able to y 3,650 nmi. up to 25,000 ft., using a 5.7 hp. engine. It will feature an de-icing system on the leading edge of its 8 ft. span wing to allow it to y through cold, moist climates. It will have a 39 in. long fuselage with a tail boom of 33 in. The aircraft has been designed to be made out of composites, thus reducing both the weight of the aircraft as well as its drag. It has been designed to come apart in order to be shipped successfully to the South Pole. There, it will be assembled and launched via a custom pneumatic launcher. It will y autonomously to 15,000 ft. and cruise climb throughout the flight to 25,000 ft., before descending to its destination. There, it will be caught by a net restraint system, where the hard drive will be extracted. The Carrier Pigeon is truly a unique vehicle for its size, range, and robustness.

During April-May 2010, the eruption of Eyjafjallajokull volcano in Iceland caused the larger breakdown of civil aviation after World War II. Although the eruption was weak in intensity, the dispersal of volcanic ash clouds over northern and central Europe resulted in more than 100.000 flights canceled and caused over USD 1.7 billion economical losses. This event and its unexpected effects raised many questions amongst the affected communities and stakeholders. How could volcanic eruptions cause severe disruptions at continental scales? Were these impacts totally unexpected? What could have been done to improve preparedness of aviation sector and reduce societal impacts of disruptions? The harmful effects of volcanic ash on aircraft's components have long been recognized, and volcanic ash dispersal patterns can be forecasted thanks to sophisticated numerical models. However, the procedures to be implemented in case of ash-contaminated airspace where applied only in few occasions, due to the relatively low frequency of explosive eruptions events. The 2010 Eyjafjallajokull crisis revealed a low preparedness of society to direct and indirect impacts of volcanic eruptions, and pointed out some flaws to be improved for mitigating impacts of explosive eruptions on aviation operations. The issues pointed out by the 2010 crisis are the starting point of this PhD research, which aims at offering new methods for improving aviation management during explosive volcanic eruptions. This manuscript describes the novel contributions developed during a 4-year period of research. The adoption of new techniques is proposed in order to improve current tephra dispersal modeling strategies and produce results focused on aviation needs. This research develops the first methodology to assess vulnerability of air traffic system and its elements to volcanic tephra dispersal. In addition, an impact assessment methodology has been designed to estimate expected impacts of explosive volcanic eruptions on the air traffic network and its elements. The impact assessment methodology has been implemented into a map-based tool to automatically assess expected impacts of volcanic eruptions based on real ash dispersal and air traffic data. Results of the vulnerability and impact assessment can support the stakeholders involved in the definition of risk-management strategies. Contributions of this research have been applied to case-studies and specific results have been published in a collection of journal papers. Main outcomes of the research are discussed identifying further work to be done in this rapidly evolving field. This research provides useful insights to reduce impacts of volcanic eruptions on civil aviation and, eventually, on the whole society.
En Abril 2010, la erupción del volcán Islandés Eyjafjallajokull causó la interrupción mas grande del tráfico aéreo en Europa desde la segunda guerra mundial. A pesar de su baja intensidad, esta erupción produjo una nube de ceniza que cubrió Europa central causando la cancelación de mas de 100.000 vuelos y perdidas económicas de más de 1.700 millones de USD. Este evento generó muchas preguntas en la opinión publica y las comunidades impactadas. ¿Pero cómo pudo una erupción volcánica provocar impactos tan fuertes a escala continental? ¿Fueron estos impactos realmente inesperados? ¿Qué se habría podido hacer para mejorar la preparación de la aviación civil? Los daños que la ceniza volcánica puede provocar en los componentes de los aviones se han documentado desde los años ochenta. También, gracias a sofisticados modelos numéricos desarrollados en las ultimas décadas, los patrones de dispersión de ceniza volcánica se pueden pronosticar. Aun así, la erupción de Eyjafjallajokull en 2010 evidenció que la sociedad no estaba preparad a lidiar con este tipo de eventos y sus impactos directos e indirectos. En Europa los procedimientos a seguir en caso de ceniza volcánica en el espacio aéreo se habían aplicado en pocas ocasiones, debido a la frecuencia relativamente baja de erupciones volcánicas explosivas. Las dificultades sufridas por los gestores del trafico aéreo en 2010 subrayan algunos aspectos a mejorar para mitigar impactos similares en el futuro. Estos aspectos son el punto de partida de esta investigación, que tiene como objetivo ofrecer nuevos métodos para mejorar la gestión del tráfico aéreo durante erupciones volcánicas explosivas. Este documento describe las contribuciones desarrolladas durante los 4 años de investigación pre-doctoral. Esta investigación propone algunas mejoras en las estrategias de modelado utilizadas actualmente para dispersión de ceniza en la atmósfera, y generar resultados que satisfagan las necesidades de la aviación civil. Se presenta la primera metodología que permite estimar la vulnerabilidad del trafico aéreo en caso de erupciones volcánicas y los impactos de la ceniza volcánica sobre sus elementos. También se ha creado una herramienta informática que permite automatizar el análisis de impactos y producir resultados utilizando datos reales de dispersión de ceniza y de trafico aéreo. Este documento discute los resultados principales de la investigación y propone directrices para su desarrollo futuro. Las contribuciones de esta investigación se han aplicado a varios casos de estudio para producir resultados específicos, y se pueden potencialmente aplicar a otras zonas. Los resultados se han presentado y discutido en un compendio de artículos científicos, publicados en revistas internacionales. Los análisis de vulnerabilidad e impacto pueden dar soporte a los actores involucrados en la gestión de trafico aéreo y la definición de estrategias para la gestión de riesgo. Sus resultados son significativos para dar soporte y definir estrategias para la gestión de riesgo. Los desarrollos futuros de esta investigación podrían utilizarse para reducir el impacto de erupciones volcánicas sobre la aviación civil, que afectan indirectamente a toda la sociedad

On April 9, 1940, Germany invaded Denmark. Instantly, the fate and status of Greenland, a Danish colony, was thrust into limbo. During the war, Greenland’s vital mineral resources and location made it significant for the warring parties on both sides of the Atlantic. However, conflicting international corporate and political interests made any act to defend the island on the part of the Allies, or the officially neutral Americans, problematic. Within a year of the Danish occupation, the American government had signed an agreement for the defense of Greenland, extending the protection of both the Monroe Doctrine and the American military to the island. This action was an important step in the formal expansion of American influence in the Western Hemisphere that occurred during the Second World War. This thesis argues that global economic, political, and technological changes led to Greenland’s increased geopolitical significance and set the stage for a shift in the balance of power within the North Atlantic Triangle. It demonstrates how decisions relating to the security of the island came to be made and how conflicting interests within and between governments affected the genesis of the occupation. It explores how Winston Churchill’s decision to mine the North Sea led to the American occupation of Greenland and examines the ways in which the effects of Churchill’s actions raised concerns in Canada about the possibility of a British defeat, which in turn led Mackenzie King, the Canadian Prime Minister, to align his foreign policy closer to that of the United States’ President Roosevelt. This thesis also asserts that Roosevelt successfully used the potential foreign occupation of Greenland to demonstrate to the American public the dangers of foreign conflicts to the United States and to further his hemispheric security objectives both domestically and abroad. These events had a profound and lasting impact on the relationships within the North Atlantic Triangle and on political identity in Greenland, and signalled an important shift in the foreign policy of the United States toward greater American involvement in world affairs.

Lau, Chi Shing = 一個應用於航空的高分辨率、快速更新的氣象數據分析系統 / 柳巳丞.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2008.
Includes bibliographical references (leaves 76-78).
Abstracts in English and Chinese.
Lau, Chi Shing = Yi ge ying yong yu hang kong de gao fen bian lu, kuai su geng xin de qi xiang shu ju fen xi xi tong / Liu Sicheng.
Abstract --- p.i
Acknowledgement --- p.iii
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Overview --- p.1
Chapter 1.2 --- Review on Windshear --- p.2
Chapter 2 --- Review of the Weather Radar System --- p.5
Chapter 2.1 --- Introduction --- p.5
Chapter 2.2 --- Reflectivity Measurement --- p.8
Chapter 2.3 --- Velocity Measurement --- p.11
Chapter 2.4 --- The Doppler Dilemma --- p.14
Chapter 2.5 --- TDWR and LIDAR used in Hong Kong --- p.16
Chapter 3 --- Design of the System --- p.19
Chapter 3.1 --- The Wind Analysis --- p.19
Chapter 3.2 --- The Cloud Analysis --- p.25
Chapter 3.3 --- Settings of the Domain --- p.26
Chapter 4 --- Data Preparation --- p.31
Chapter 4.1 --- Background Field --- p.31
Chapter 4.2 --- Non-radar Observation Data --- p.33
Chapter 4.3 --- The Radar Data --- p.33
Chapter 5 --- A Study on Sea Breeze --- p.37
Chapter 5.1 --- The Physical origin of Sea Breeze --- p.37
Chapter 5.2 --- Case Study on 10 March 2006 --- p.41
Chapter 6 --- A Study on Tropical Cyclone --- p.46
Chapter 6.1 --- The Physics of Tropical Cyclone --- p.46
Chapter 6.2 --- Case Study on 3 Aug 2006 --- p.51
Chapter 7 --- A Study on Microburst --- p.57
Chapter 7.1 --- The Physical origin of Microburst --- p.57
Chapter 7.2 --- Case Study on 8 June 2007 --- p.60
Chapter 8 --- Discussions and Conclusions --- p.67
Chapter 8.1 --- Discussions --- p.67
Chapter 8.2 --- Conclusions --- p.69
Chapter A --- Derivation of Radar Equation --- p.70
Chapter A.1 --- Radar Equation for Point Target --- p.70
Chapter A.2 --- Radar Equation for Distributed Targets --- p.71
Chapter B --- Technical Details --- p.73
Chapter B.1 --- Hardware and Timing --- p.73
Chapter B.2 --- Programming issues --- p.75
Bibliography --- p.76

Weather-related delays in the aviation sector will always occur, however, through effective delay management and improved weather forecasting, the impact and duration of delays can be reduced. The research examined the type of weather that caused departure delays, due to adverse weather at the departure station, namely O. R. Tambo International Airport (ORTIA), over the period 2010 to 2013. It was found that the most significant weather that causes such delays are thunderstorms, followed by fog. Other noteworthy elements are rainfall, without the influence of other weather elements, and icing. It was also found that the accuracy of a weather forecast does not impact on the number of departure delays, and thus departure delays due to weather at the departure station are largely unavoidable. However, the length and impact of such delays can be reduced through improved planning. The study highlights that all weather-related delays can be reduced by improved weather forecasts, effective assessment of the weather forecast, and collaborative and timely decision making. A weather impact index system was designed for ORTIA and recommendations for delay reductions are made.
Geography
M. Sc. (Geography)

Presented graduation thesis is focused on the life and public activity of the teacher at the secondary school Jaroslav Maňák. By his activity and sedulity he had merit in prosperity of club life in České Budějovice. We owe him to the development of amateur flying (sporting aviation) in South Bohemia. The thesis is divided into five main chapters except the oddments. The first chapter shortly deals with the whole life of Jaroslav Maňák. The second chapter describes level of secondary education in the town and his pedagogic activity. The most extensive chapter devoted to aviation follows this part. It is divided into six subchapters and I introduce the field of the greatest interest of Jaroslav Maňák. The next chapter deals with the meteorologic observation and it also resumes level of observation before Maňák{\crq}s activity. The last fifth chapter deals with Maňák{\crq}s activity in lesser-known associations in the town. Each association has got its separate subchapter. The Epilogue, which recapitulates the career and activity of personality, is followed by the list of used sources, literature and presentation of supplements.

Honeywell Technology Solutions Lab, India
Weather is a major contributing factor in aviation accidents, incidents and delays. Doppler weather radar has emerged as a potent tool to observe weather. Aircraft carry onboard radars but their range and angular resolution are limited. Networks of ground-based weather radars provide extensive coverage of weather over large geographic regions. It would be helpful if these data can be transmitted to the pilot. However, these data are highly voluminous and the bandwidth of the ground-air communication links is limited and expensive. Hence, these data have to be compressed to an extent where they are suitable for transmission over low-bandwidth links. Several methods have been developed to compress pictorial data. General-purpose schemes do not take into account the nature of data and hence do not yield high compression ratios. A scheme for extreme compression of weather radar data is developed in this thesis that does not significantly degrade the meteorological information contained in these data. The method is based on contour encoding. It approximates a contour by a set of systematically chosen ‘control points’ that preserve its fine structure up to a certain level. The contours may be obtained using a thresholding process based on NWS or custom reflectivity levels. This process may result in region and hole contours, enclosing `high' or `low' areas, which may be nested. A tag bit is used to label region and hole contours. The control point extraction method first obtains a smoothed reference contour by averaging the original contour. Then the points on the original contour with maximum deviation from the smoothed contour between the crossings of these contours are identified and are designated as control points. Additional control points are added midway between the control point and the crossing points on either side of it, if the length of the segment between the crossing points exceeds a certain length. The control points, referenced with respect to the top-left corner of each contour for compact quantification, are transmitted to the receiving end. The contour is retrieved from the control points at the receiving end using spline interpolation. The region and hole contours are identified using the tag bit. The pixels between the region and hole contours at a given threshold level are filled using the color corresponding to it. This method is repeated till all the contours for a given threshold level are exhausted, and the process is carried out for all other thresholds, thereby resulting in a composite picture of the reconstructed field. Extensive studies have been conducted by using metrics such as compression ratio, fidelity of reconstruction and visual perception. In particular the effect of the smoothing factor, the choice of the degree of spline interpolation and the choice of thresholds are studied. It has been shown that a smoothing percentage of about 10% is optimal for most data. A degree 2 of spline interpolation is found to be best suited for smooth contour reconstruction. Augmenting NWS thresholds has resulted in improved visual perception, but at the expense of a decrease in the compression ratio. Two enhancements to the basic method that include adjustments to the control points to achieve better reconstruction and bit manipulations on the control points to obtain higher compression are proposed. The spline interpolation inherently tends to move the reconstructed contour away from the control points. This has been somewhat compensated by stretching the control points away from the smoothed reference contour. The amount and direction of stretch are optimized with respect to actual data fields to yield better reconstruction. In the bit manipulation study, the effects of discarding the least significant bits of the control point addresses are analyzed in detail. Simple bit truncation introduces a bias in the contour description and reconstruction, which is removed to a great extent by employing a bias compensation mechanism. The results obtained are compared with other methods devised for encoding weather radar contours.

Weather is a major contributing factor in aviation accidents, incidents and delays. Doppler weather radar has emerged as a potent tool to observe weather. Aircraft carry onboard radars but their range and angular resolution are limited. Networks of ground-based weather radars provide extensive coverage of weather over large geographic regions. It would be helpful if these data can be transmitted to the pilot. However, these data are highly voluminous and the bandwidth of the ground-air communication links is limited and expensive. Hence, these data have to be compressed to an extent where they are suitable for transmission over low-bandwidth links. Several methods have been developed to compress pictorial data. General-purpose schemes do not take into account the nature of data and hence do not yield high compression ratios. A scheme for extreme compression of weather radar data is developed in this thesis that does not significantly degrade the meteorological information contained in these data. The method is based on contour encoding. It approximates a contour by a set of systematically chosen ‘control points’ that preserve its fine structure up to a certain level. The contours may be obtained using a thresholding process based on NWS or custom reflectivity levels. This process may result in region and hole contours, enclosing `high' or `low' areas, which may be nested. A tag bit is used to label region and hole contours. The control point extraction method first obtains a smoothed reference contour by averaging the original contour. Then the points on the original contour with maximum deviation from the smoothed contour between the crossings of these contours are identified and are designated as control points. Additional control points are added midway between the control point and the crossing points on either side of it, if the length of the segment between the crossing points exceeds a certain length. The control points, referenced with respect to the top-left corner of each contour for compact quantification, are transmitted to the receiving end. The contour is retrieved from the control points at the receiving end using spline interpolation. The region and hole contours are identified using the tag bit. The pixels between the region and hole contours at a given threshold level are filled using the color corresponding to it. This method is repeated till all the contours for a given threshold level are exhausted, and the process is carried out for all other thresholds, thereby resulting in a composite picture of the reconstructed field. Extensive studies have been conducted by using metrics such as compression ratio, fidelity of reconstruction and visual perception. In particular the effect of the smoothing factor, the choice of the degree of spline interpolation and the choice of thresholds are studied. It has been shown that a smoothing percentage of about 10% is optimal for most data. A degree 2 of spline interpolation is found to be best suited for smooth contour reconstruction. Augmenting NWS thresholds has resulted in improved visual perception, but at the expense of a decrease in the compression ratio. Two enhancements to the basic method that include adjustments to the control points to achieve better reconstruction and bit manipulations on the control points to obtain higher compression are proposed. The spline interpolation inherently tends to move the reconstructed contour away from the control points. This has been somewhat compensated by stretching the control points away from the smoothed reference contour. The amount and direction of stretch are optimized with respect to actual data fields to yield better reconstruction. In the bit manipulation study, the effects of discarding the least significant bits of the control point addresses are analyzed in detail. Simple bit truncation introduces a bias in the contour description and reconstruction, which is removed to a great extent by employing a bias compensation mechanism. The results obtained are compared with other methods devised for encoding weather radar contours.
Honeywell Technology Solutions Lab, India

Weather is a major contributing factor in aviation accidents, incidents and delays. Doppler weather radar has emerged as a potent tool to observe weather. Aircraft carry an onboard radar but its range and angular resolution are limited. Networks of ground-based weather radars provide extensive coverage of weather over large geographic regions. It would be helpful if these data can be transmitted to the pilot. However, these data are highly voluminous and the bandwidth of the ground-air communication links is limited and expensive. Hence, these data have to be compressed to an extent where they are suitable for transmission over low-bandwidth links. Several methods have been developed to compress pictorial data. General-purpose schemes do not take into account the nature of data and hence do not yield high compression ratios. A scheme for extreme compression of weather radar data is developed in this thesis that does not significantly degrade the meteorological information contained in these data. The method is based on contour encoding. It approximates a contour by a set of systematically chosen ‘control’ points that preserve its fine structure upto a certain level. The contours may be obtained using a thresholding process based on NWS or custom reflectivity levels. This process may result in region and hole contours, enclosing ‘high’ or ‘low’ areas, which may be nested. A tag bit is used to label region and hole contours. The control point extraction method first obtains a smoothed reference contour by averaging the original contour. Then the points on the original contour with maximum deviation from the smoothed contour between the crossings of these contours are identified and are designated as control points. Additional control points are added midway between the control point and the crossing points on either side of it, if the length of the segment between the crossing points exceeds a certain length. The control points, referenced with respect to the top-left corner of each contour for compact quantification, are transmitted to the receiving end. The contour is retrieved from the control points at the receiving end using spline interpolation. The region and hole contours are identified using the tag bit. The pixels between the region and hole contours at a given threshold level are filled using the color corresponding to it. This method is repeated till all the contours for a given threshold level are exhausted, and the process is carried out for all other thresholds, thereby resulting in a composite picture of the reconstructed field. Extensive studies have been conducted by using metrics such as compression ratio, fidelity of reconstruction and visual perception. In particular the effect of the smoothing factor, the choice of the degree of spline interpolation and the choice of thresholds are studied. It has been shown that a smoothing percentage of about 10% is optimal for most data. A degree 2 of spline interpolation is found to be best suited for smooth contour reconstruction. Augmenting NWS thresholds has resulted in improved visual perception, but at the expense of a decrease in the compression ratio. Two enhancements to the basic method that include adjustments to the control points to achieve better reconstruction and bit manipulations on the control points to obtain higher compression are proposed. The spline interpolation inherently tends to move the reconstructed contour away from the control points. This has been somewhat compensated by stretching the control points away from the smoothed reference contour. The amount and direction of stretch are optimized with respect to actual data fields to yield better reconstruction. In the bit manipulation study, the effects of discarding the least significant bits of the control point addresses are analyzed in detail. Simple bit truncation introduces a bias in the contour description and reconstruction, which is removed to a great extent by employing a bias compensation mechanism. The results obtained are compared with other methods devised for encoding weather radar contours.