Dissertations / Theses on the topic 'Herbicide efficiency in rain'

Rain gardens are low impact developments designed to mitigate a suite of issues associated with urban stormwater runoff. The site for this study was a Denton City rain garden at the Denton Waste Water Treatment Plant. Nitrogen and phosphorus removal was examined in light of two overflow events comprised of partially treated wastewater from an upslope anaerobic digester pond. Nitrate removal efficiency was examined across differing dry spell intervals of 5, 8, and 12 d, displaying a moderate negative correlation (r2 = 0.59). Continued phosphorus removal capacity was assessed, showing phosphorus removal in cases where P was in excess of 0.8 mg/L, reflecting an equilibrium phosphorus concentration. A high expanded shale component in the soil media (25%) was likely a factor in the continued removal of phosphorus. Overall the rain garden proved to be a large source of nitrate (+425%) and total nitrogen (+61%) by mass. The study showed that while the rain garden intercepted a large volume of partially treated wastewater during the overflow events, preventing it from reaching a nearby creek, the mitigation of an acute event has extended to a chronic one as nitrogen is gradually processed and flushed from the system as nitrate.

There has been little research into the compatibility of commonly utilized apple rootstocks and VA-fungal types, and even less research regarding the effects of herbicides used in orchards, on the VAM symbiosis of apple trees. Studies demonstrated that early inoculation of young apple plants, prior to transplanting, results in healthy and vigorous plants with better growth and nutrition than uninoculated plants. We studied the efficiency of VA-fungal species and isolates on young apple rootstocks, produced by in vitro propagation. Mycorrhizal inoculation promoted plant growth, dry mass production and leaf P concentration. Mycorrhizal efficiency was associated with larger external hyphal network but showed no relation with the internal colonization. Despite the high P-fertility of the soil used, growth enhancement due to mycorrhizal inoculation was attributed to an improved P nutrition.
In a second experiment, the effect of herbicides currently used in orchards was tested on the mycorrhizal symbiosis. Paraquat, simazine and dichlobenil were applied to soil with mycorrhizal and non-mycorrhizal apple plants. Mycorrhizae increased herbicide toxicity in apple, as demonstrated by the greatly increased plant mortality. While both paraquat and simazine decreased spore germination in vitro, none of the herbicide treatments affected root colonization in soil. Effects on the photosynthetic rate, measured after herbicide application, indicated a physiological interaction between mycorrhizal colonization and dichlobenil, involved in the toxic response of apple plants.

Urbanisation leads to increases in stormwater runoff, resulting in elevated contaminant (e.g. metal, sediment, and nutrient pollutant) loads, decreased local infiltration and greater peak flow intensities. Heavy metal contaminants of concern, primarily copper (Cu), lead (Pb), and zinc (Zn), originate from a variety of sources including wear-and-tear of vehicle parts, corrosion of alloy roofs, legacy petroleum contamination, and multifarious construction practices. Different technologies have been used to mitigate stormwater runoff, ranging from traditional drainage networks fitted with concrete proprietary devices (e.g. vortex sediment separators and filters) to more environmentally integrated sustainable solutions. Rain gardens, a type of Sustainable Urban Drainage System (SUDS) or Water Sensitive Urban Design (WSUD), are employed to control stormwater peak flows and runoff volumes and simultaneously reduce contaminant loads to neighbouring waterways through biologically-active landscaped design. Despite increases in use of rain gardens as a best management practice (BMP) to treat urban stormwater runoff, there is a dearth of knowledge about their treatment and infiltration performance worldwide. It is believed that incorporating topsoil into rain garden design is likely to improve contaminant removal efficiencies (Davis et al. 2001; ARC 2003; Fletcher et al. 2004; Carpenter and Hallam 2010), but design recommendations are not informed by performance data which is limiting. Performance data is necessary for understanding the long-term responses of bioinfiltrative treatment systems and for modelling efforts aiming to predict their mitigation behaviour (Fletcher et al. 2004). In order to evaluate the influence of substrate composition on stormwater treatment and hydraulic effectiveness in rain gardens, mesocosm-scale (180 L, 0.17 m2) laboratory systems were established. Saturated (constant-head) hydraulic conductivity was determined before and after contaminant (Cu, Zn, Pb and nutrients) removal experiments on three rain garden systems comprising various proportions of organic topsoil. Raw stormwater runoff from a neighbouring Christchurch city catchment was collected, characterised, and applied in the removal efficiency experiments. The system with only topsoil had the lowest saturated hydraulic conductivity (160 mm/hr initial to 164 mm/hr final) and poorest metal (Cu, Zn) removal efficiency (Cu 0.3%, Zn 60.5% and Pb 89.5%) at a ‘standard’ contaminant loading rate (Cu = 5.99 ± 0.73 µg/min, Zn = 57.89 ± 6.06 µg/min, Pb = 13.65 ± 2.80 µg/min). The sand-only system demonstrated good metal removal (Cu 56.4%, Zn 73.5%, and Pb 81.6%) with hydraulic conductivity (up to 805 mm/hr) adequate for practical implementation (i.e. greater than the 13 mm/hr minimum requirement (ARC 2003; MDE 2009; SFPUC 2009)). Overall, total metal amounts in the effluent were <50% of influent loads for all experiments, with the exception of Cu in the topsoil-only system, whose removal was negligible (0.3%). Greater metal removal was observed when effluent pH was elevated (up to pH 7.38). The pH increase (from an initial pH of 6.23 in raw stormwater) was provided by the calcareous sand, whereas the topsoil-only system lacked an alkaline source. Consequently, organic topsoil had poorer contaminant removal due to higher dissolved metal fractions, which are more difficult to immobilise at the lower pH. The relationship between pH and dissolved fraction was highly significant (Pearson’s Correlation, p < 0.0001, df = 74) for Cu, Zn, and Pb. Mesocosm-scale systems were then re-established with a calcareous substrate supplement to quantify the effects of pH augmentation on contaminant removal and hydraulic efficiencies. Mussel shells, a waste product from the shell-fish industry, were employed in two different volumetric proportions. Metal removal efficiency was increased in systems with mussel shells (Cu up to 46.6%, Zn up to 80.2%, Pb up to 88.7%) compared to the topsoil-only system (Cu 27.5%, Zn 55.5%, Pb 81.0%). Larger increases in removal efficiency were seen for Cu and Zn because increases in pH from mussel shell enhanced particulate fractions, which are easier to remove in filtration systems, while Pb is mainly in the particulate form at influent pH (Morrison et al. 1990). Effluent from systems with mussel shells also had higher hardness (hardness up to 101.7 mg/L as CaCO3) compared with 22.4 mg/L as CaCO3 in topsoil-only effluent. Hardness reduces metal ecotoxicity (Hyne et al. 2005). Results of these experiments show that mussel shells are a promising rain garden substrate capable of increasing metal removal efficiency and also decreasing metal ecotoxicity in effluent of bioinfiltration systems. Concurrently, an operational field-scale “rain garden” (42 m3; 60 m2) in Christchurch was monitored for hydraulic throughput and contaminant removal. The field system performed extremely well at mitigating peak flows, detaining water throughout storm events and removing total suspended solids (TSS) (90.6% average removal). However, the system failed to reduce effluent median total metal concentrations (Cu = 15.9 µg/L, Zn = 139.6 µg/L, Pb = 11.7 µg/L) below relevant ANZECC guidelines (Cu = 1.8 µg/L, Zn = 15.0 µg/L, Pb = 5.6 µg/L) highlighting the opportunity to optimise these field designs to improve metal removal.

In this study, the relationship of above-ground net primary productivity (ANPP) with precipitation using the enhanced vegetation index (EVI) from satellite data as surrogate for ANPP was assessed. To use EVI as a proxy for ANPP we extracted the satellite data from areas with uniform vegetation in a 2x2 km area for the multi-site approach.In the multi-site analysis in the United States our results showed a strong exponential relationship between iEVI and annual precipitation across the sites and climate regimes studied. We found convergence of all sites toward common and maximum rain use efficiency under the water-limited conditions represented by the driest year at each site. Measures of inter-annual variability in iEVI with rainfall variation across biomes were similar to that reported by Knapp and Smith (2001) in which the more herbaceous dominant sites were found to be most sensitive to interannual variations in precipitation with no relationships found in woodland sites.The relationship was also evaluated in the southern hemisphere using a multi-site analysis with information from satellite TRMM for precipitation and MOD13Q1 from MODIS for EVI values at calendar and hydrologic year periods. The tested sites were located across the 6 major land cover types inAustralia, obtained from MODIS MCD12Q1 product and used to compare the relationship across different biomes. The results showed significant agreement between the annual iEVI and annual precipitation across the biomes involved in this study showing non-significant differences between the calendar and hydrologic years for the 24 sites across different climatic conditions.At the regional scale we also assessed the ANPP-precipitation relationship across all of Australia. Precipitation data from TRMM was obtained at 0.25x0.25 degrees spatial resolution and monthly temporal resolution and EVI values were obtained from the CGM (Climate Grid Modeling) MOD13C1-16-days and 5.6km temporal and spatial resolutions, respectively. Our results were in fair agreement with those from our first two studies and previous research and provided specific insights regarding the use iEVI as a proxy for productivity over extended regions as well as its combination with data sets from TRMM sensor for precipitation data.

Les particules d'aérosol sont une composante essentielle de l'atmosphère, et cette importance s'amplifie lors d'une éventuelle libération dans l'atmosphère de matières radioactives sous forme particulaire. En effet, pour améliorer la connaissance autour de la contamination des sols consécutive à une émission de particules, il est important d'étudier le rabattement des particules par la pluie sous le nuage. Dans ce but, des expériences sont menées à l'échelle microphysique (expérience BERGAME) pour quantifier l'efficacité des gouttes de pluie à collecter les particules. Ceci permet au final d'améliorer la modélisation du lessivage des aérosols atmosphériques par la pluie à méso-échelle. Le modèle utilisé est DESCAM qui décrit de manière détaillée les distributions granulométriques en masse et en nombre des particules pour chaque type d'aérosol et des hydrométéores et calcule leur évolution due aux processus microphysiques nuageux. L'expérience BERGAME a été dimensionnée et construite pour mesurer l'efficacité de collecte car les mesures de ce paramètre se sont avérées en désaccord avec les modèles classiques de la littérature pour les gouttes de pluie d'un diamètre supérieur au millimètre. Un montage optique a été imaginé pour tenter de comprendre quels mécanismes de collecte sont négligés dans les modèles standards. Un nouveau modèle d'efficacité de collecte pour les gouttes d'un diamètre de 2 mm est alors proposé prenant en compte pour les grosses gouttes une recirculation turbulente dans le sillage de la goutte capable d'augmenter de façon importante la capture des petites particules. Les nouvelles efficacités de collecte ainsi mesurées et paramétrées sont ajoutées au modèle de nuage DESCAM. Des modifications significatives sur la modélisation du lessivage par DESCAM sont observées, ouvrant ainsi la voie à une amélioration de la modélisation de la contamination des sols par les modèles de dispersion atmosphérique.

碩士
中國科技大學
建築系
104
Taiwan area rainfall characteristics change significantly over recent years, increasing frequency of heavy rainfall, directly affect the efficiency of the drainage to the roof of the building; the poor drainage of the roof, to make people aware of the roof drainage patterns should rethink strategy. Greater Taipei basin topography, rainfall of climate change more likely. Roof drainage effectiveness was quite limited due to strong rainfall, seriously affected the damage to the building's roof, very easy to produce the phenomenon of roof water. To understand the strong rainfall on the building's roof drainage patterns in water, this study will be to gather in Taipei and his island nation Japan Tokyo roof drainage patterns of data, under heavy rain, comparative analysis of water drainage patterns and head diameter drainage impact effectiveness. First of all understand what happened in recent years several poor drainage caused by heavy rains induced by the roof of the typical examples of leaky roofs, analysis Taipei in leak case induced by heavy rainfall on the basis of, if you have good drainage effect of hedge of leaking roofs. Basis this study has put more emphasis on the literature review and data collection, and the collection and investigation of cases in order to clarify the roof drainage system related topics then analyzed the roof drainage system design specification sort, and experimentally drainage slope and displacement, with computer software checked drainage performance of qualitative factors. The results of this study include: a literature review of the drainage system of physical phenomena, Foundation of the relevant research data, set up several kinds of factors that affect the roof drainage; investigation and experimental analysis, master drainage effectiveness.

Precise engineering of genomes holds great promise to advance our understanding of gene function and biotechnological applications. DNA double strand breaks are repaired via imprecise non-homologous end joining repair or via precise homology-directed repair processes. Therefore, we could harness the DSBs to engineer the genomes with a variety of genetic outcomes and with singlebase- level precision. The major barrier for genome engineering was the generation of site-specific DNA DSBs. Programmable DNA enzymes capable of making a complete and site-specific cut in the genome do not exist in nature. However, these enzymes can be made in in vitro as chimeric fusions of two modules, a DNA binding module and a DNA cleaving module. The DNA cleaving module can be programmed to bind to any user-defined sequence and the DNA cleaving module would generate DSBs in the target sequence. These enzymes called molecular scissors include zinc finger nucleases (ZFNs) and transcriptional activator like effector nucleases (TALENs). The programmability of these enzymes depends on protein engineering for DNA binding specificity which may be complicated, recourse intensive and suffer from reproducibility issues. Recently, clustered regularly interspaced palindromic repeats (CRISPR)/ CRISPR associated endonuclease 9 (Cas9) an adaptive immune system of bacterial and archaeal species has been developed for genome engineering applications. CRISPR/Cas9 is an RNA-guided DNA endonuclease and can be reprogrammed through the engineering of single guide RNA molecule (sgRNA). CRISPR/Cas9 activity has been shown across eukaryotic species including plants. Although the engineering of CRISPR/Cas9 is quite predictable and reproducible, there are many technological challenges and improvements that need to be made to achieve robust, specific, and efficient plant genome engineering. Here in this thesis, I developed a number of technologies to improve specificity, delivery and expression and heritability of CRISRP/Cas9-modification in planta. Moreover, I used these technologies to answer basic questions to understand the molecular underpinning of the interplay between splicing and abiotic stress. To improve Cas9 specificity, I designed and constructed a chimeric fusion between catalytically dead Cas9 (dCas9) and FOKI catalytic DNA cleaving domain (dCas9.FoKI). This synthetic chimeric fusion enzyme improved Cas9 specificity which enable precision genome engineering. Delivery of genome engineering reagents into plant cells is quite challenging, I developed a virus-based system to deliver sgRNAs into plants which facilitates plant genome engineering and could bypass the need for tissue culture in engineering plant genomes. To improve the expression of the CRISPR/Cas9 machinery in plant species, I developed a meiotically-driven expression of CRISPR/Cas9 which improved genome editing and heritability of editing in seed progeny, thereby facilitating robust genome engineering applications. To understand the molecular basis of the interplay between splicing stress and abiotic stress, I used the CRISPR/Cas9 machinery to engineer components of the U2snRNP complex coupled which chemical genomics to understand the splicing stress regulation in response to abiotic stress conditions. Finally, I harnessed the technological improvements and developments I have achieved with CRISPR/Cas9 system to develop a directed evolution platform for targeted trait engineering which expands and accelerates trait discovery and engineering of plant species resilient to climate change conditions.

This work is focused on verification of the effect of chosen herbicides on Weeds occuring in sprouts of spring barley which i sone of the main crops grown in the territory of the Czech Republic. Lately, herbicides have influenc the Šeld of spring barley. So as to verify the herbicide efficiency there was founded a small parcel o fland test where there was assessed the efficiency of postmergent herbicides on Leeds which occurred in all parcels and during all the observation. The efficiency was observed on four measurements and it was recorded in percentage by Subjective Estimation Methods. The chosen postmergent herbicides took a very good effect on singl Leeds. As the best effective herbicide could be, hawevr, indicated Sekator OD which operand on all the Leeds the same way as the Catalogue of Preparation for Plant Protection 2012 states. Out of the results of efficiencies and overalobservations of tested area it can be stated that despote good preventative measures the protection of spring barley can not dispense with higt quality treatment with verified herbicides.

Student Number : 9511039F - MSc Dissertation - School of Animal, Plant and Environmental Sciences - Faculty of Science
An estimated 91 % of South Africa’s total land area is considered dryland and susceptible to desertification. In response, South Africa has prepared a National Action Programme to combat land degradation, and this requires assessment and monitoring to be conducted in a systematic, cost effective, objective, timely and geographically-accurate way. Despite a perception-based assessment of land degradation conducted in 1999, and a land-cover mapping exercise conducted for 2000/2001, there are few national scientifically rigorous degradation monitoring activities being undertaken, due largely to a lack of objective, quantitative methods for use in large-scale assessments. This study therefore tests a satellitederived index of degradation for the Limpopo Province in South Africa, which is perceived to be one of the most degraded provinces in the country. The long-term average maximum normalized difference vegetation index (NDVI), calculated from a time series (1985-2004) of NOAA AVHRR satellite images, as a proxy for vegetation productivity, was related to water balance datasets of mean annual precipitation (MAP) and growth days index (GDI), using both linear and non-linear functions. Although the linear regressions were highly significant (p<0.005), a non-linear four parameter Gompertz curve was shown to fit the data more accurately. The curve explained only a little of the variance in the data in the relationship between NDVI and GDI, and so GDI was excluded from further analysis. All pixels that fell below a range of threshold standard deviations less than the fitted curve were deemed to represent degraded areas, where productivity was less than the predicted value. The results were compared qualitatively to existing spatial datasets. A large proportion of the degraded areas that were mapped using the approach outlined above occurred on areas of untransformed savanna and dryland cultivation. However the optical properties of dark igneous derived soils with high proportions of smectitic minerals and therefore low reflectance, were shown to lower NDVI values substantially. Overall, there was an acceptable agreement between the mapped degradation and the validation datasets. While further refinement of the methodology is necessary, including a rigorous field-based resource condition assessment for validation purposes, and research into the biophysical effects on the NDVI values, the methodology shows promise for regional assessment in South Africa.

碩士
國立中興大學
應用經濟學系所
105
This study used a Cobb-Douglas Stochastic Frontier model with a heteroskedastic error structure to investigate Technical efficiency and Cost efficiency of rice farm smallholders in central region of Burkina Faso, West Africa. Allocative efficiency was derived from the two latter aforementioned. A one-stage Maximum-likelihood approach is simultaneously applied with the inefficiency model to identify the determinants factors underlying efficiency differentials among the sampled farming households. Results revealed an average technical, economic and allocative efficiency levels of 76.38%, 84.08% and 60.93% respectively. This suggests that allocative efficiency offer a higher scope for improvements with potential with 39.07%, compared to 23.62% opportunity to enhance technical efficiency, and 15.92% in economic efficiency. An interesting implication emerging from the study is that farmers are operating with substantial Technical and Economic inefficiencies and hence have possibility to raise the profitability of rice production by fully adjusting inputs use. Moreover, Age of farm manager, Access to extension services, Access to input credit, Household size, and Year of cropping were the most influential factors of efficiency levels of smallholder rice farmers.

碩士
淡江大學
水資源及環境工程學系
87
Ⅰ. Determination of the Chemical Oxgen Demand in the Wastewater Using Microwave Energy — The Comparison Between the Closed Method And the Open Focus Reflux Method. In environmental analytic chemistry microwave-assisted methods for sample preparation have been increased rapidly in recent years .The closed vessel method and open focus reflux method were used for the determination of chemical oxygen demand (COD) in the digestion-oxidation step which was by using microwave energy. The goals of this study are to develop the mercury-free microwave assisted,digestion for COD determination and to compare between the open focus microwave and the closed vessel sample preparation methods. The optimized conditions for the closed vessel method are： sample, 5ml； sulfuric acid(0.55﹪Ag+), 7ml；0.0705M silver nitrate,1ml； 0.0417M potassium dichromate, 2ml； power(using domestic microwave oven): 512 W, reaction time: 5mins. The optimized conditions for the open focus reflux method are： sample, 5ml； sulfuric acid(0.55﹪Ag+), 7ml；0.0705M silver nitrate,1ml； 0.0417M potassium dichromate, 2ml； power(using open focus microwave oven): 300W, reaction time: 5mins. The average recovery of the closed vessel method for quality control samples were 98.3﹪and S. D. 1.8﹪.The average recovery of the open focus reflux method for quality control samples was 98.7﹪and S. D. 1.2﹪The ratio between COD values, determined by the open focus method and the closed vessel methods is 0.9360. The results show that both methods are comparable. Ⅱ. Determination the Efficiency of Detection Chemical and Physical Components for the Rainwater in Chung-Li Area by Acid rain Automatic Monitoring. The aims of this study are to characterize the rainfalls by physical and chemical parameter Chung-Li area and to compare the data from acid rain monitor with the results obtained in the laboratory. The physical and chemical parameters included temperature, rainfalls intensity, electrical conductivity, turbidity, pH value cation concentration (Na+,K+,NH4+,Ca2+,Mg2+) and anion concentration( Cl-,NO3-,SO42-).The results showed that the pH values, temperature, rainfalls intensity and electrical conductivity were very good as compared with that from the lab. However, the sulfate and nitrate by acid rain monitor, s spectrophotometer were poor probably because of bubbles and contamination in the line . Ion chromatography with conductivity detector has been used to determine cations and anions separately. The nitric acid solution(0.5mM) was used with cation-exchange column (MCI GEL SCK01) having low cation exchange capacities. The dilute 3mM Vanillin Acid and 2.8mM N-Methydiethanolamine(pH6.2) have been the main eluent species used for anions. The result shows the range of ratios (SO42 /NO3-)was 1~5 and the range of pH values were 4~7 for the rainwater in Chung-Li area.

This study investigated methods to reduce herbicide application through improved targeting of weeds, thereby also reducing damage to pastures. The focus was to evaluate and improve wiper and spot-spraying application techniques for pasture herbicides as they reduce chemical use by treating just the weed. Wiper application of herbicides was shown to be a useful technique for controlling Californian thistles. In one trial, a stem reduction of over 90% when assessed 10 months post application was achieved with a double pass of clopyralid, metsulfuron and glyphosate when the plants were treated at the post-flowering stage and were vigorously growing. A double pass was superior to a single pass for glyphosate and triclopyr/picloram, but not for clopyralid and metsulfuron. Subsequent trials produced poor results possibly because of the stressed condition of the thistles and their growth stage as well as lack of consistency in wiper output and operator differences. Despite wiper applicators usually being selective, some damage to pastures was observed in the field, and from a series of experiments it was concluded that rain falling soon after wiper application was the likely cause of pasture damage. An innovative and highly sensitive technique using a spectrophotometer was developed to measure herbicide output from wiper applicators. A spectrophotometer could accurately measure clopyralid concentrations as low as 0.02 g active ingredient in a litre of water. The Eliminator and Rotowiper outputs were found to be highly variable while the Weedswiper was more consistent although it applied less herbicide than the other two wipers. Spot spraying experiments confirmed that glyphosate and metsulfuron create bare patches by damaging both grass and clover while clopyralid and triclopyr/picloram only eliminate clover. However, metsulfuron patches stayed bare for much longer while glyphosate ones quickly filled up with weeds and clover. Ingress of clover stolons appeared to be more important than re-establishment from seed in the recovery of patches. The bigger the damaged patch, the higher the likelihood of recolonisation by opportunistic weeds. Bioassay studies found that over-application of clopyralid and triclopyr/picloram provided residual activity up to 18 and 30 weeks, respectively, thereby potentially preventing re-establishment of white clover. The negative effects on clover seedlings from metsulfuron ranged from 3 to 6 weeks for standard and high rates, respectively, with a stimulatory effect on seedlings thereafter for up to 18 weeks. Dose-response curves for the application of metsulfuron and triclopyr/picloram into the centre 5% versus full plant coverage of Scotch thistle and ragwort rosettes showed that application of herbicide to the centre 5% was as effective at the same concentration and greatly reduced the risk of damage to pasture.

This work focuses on high-capacity spectral-efficient Earth-space microwave communication links, supporting the access to wider and less congested bandwidths and providing the required technological advances on radiowave propagation for the design and operation of system-technologies improving the spectral efficiency, proposing the operation of frequency-reuse schemes and polarization diversity techniques at Ka- and Q/V-bands. Because the suitable planning, successful deployment and effective, spectralefficient and interference-free, operation of all space-borne systems and services is necessarily related and directly dependent, although not exclusively, on the propagation channel conditions, this work provides a comprehensive and systematic approach intending the relevant propagation phenomena characterization and understanding, modelling and mitigation. It is proved that there is a bigger operational margin for the operation of the abovementioned system-technologies than what may be believed by considering the international recommended models. Major challenges are envisaged, specially in what concerns the ice-induced depolarization that is more persistent and takes longer than the corresponding rain-induced effects. Nevertheless, their mitigation is possible for which the depolarization shall be the controlling variable. The time lag of 15 minutes is identified as the best trade-off between affordable time and achievable gain in the framework of a time diversity scheme.
Este trabalho foca-se em links de comunicação Terra-espaço em microondas espectralmente eficientes e de elevada capacidade, suportando o acesso a larguras de banda maiores e menos congestionadas e ofereçendo os avanços tecnológicos necessários em termos de propagação de ondas de rádio para o projeto e operação de tecnologias de sistema que visam o uso otimizado do espectro, propondo a operação de esquemas de reuso de frequência e de técnicas de diversidade de polarização nas bandas Ka e Q/V. Porque o adequado planeamento, a implementação bem sucedida, bem como a efetiva operação, espectralmente eficiente e livre de interferências, de todos os sistemas e serviços espaciais está necessariamente relacionada e diretamente dependente, ainda que não exclusivamente, das condições do canal de propagação, este trabalho oferece uma abordagem completa e sistemática pretendendo a caracterização, compreensão, modelação e mitigação dos fenómenos de propagação relevantes. É provado existir uma maior margem operacional para a operação das tecnologias acima mencionadas do que aquela que se acredita existir considerando os modelos internacionais recomendados. São previstos maiores desafios, especialmente no que concerne à despolarização causada por gelo que é mais persistente e que dura mais tempo do que os correspondentes efeitos causados por chuva. De qualquer forma, a sua mitigação é possível e para a qual a despolarização deverá ser a variável de controlo. O intervalo de tempo de 15 minutos é identificado como o melhor compromisso entre tempo acessível e ganho alcançável no contexto de um esquema de diversidade temporal.
Programa Doutoral em Engenharia Eletrotécnica