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1
Tshisaphungo, Mpho. "Validation of high frequency propagation prediction models over Africa". Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1015239.
Testo completoAbstract (sommario):
The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.
2
Opperman, B. D. L. "Reconstructing ionospheric TEC over South Africa using signals from a regional GPS network". Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1005273.
Testo completoAbstract (sommario):
Radio signals transmitted by GPS satellites orbiting the Earth are modulated as they propagate through the electrically charged plasmasphere and ionosphere in the near-Earth space environment. Through a linear combination of GPS range and phase measurements observed on two carrier frequencies by terrestrial-based GPS receivers, the ionospheric total electron content (TEC) along oblique GPS signal paths may be quantified. Simultaneous observations of signals transmitted by multiple GPS satellites and observed from a network of South African dual frequency GPS receivers, constitute a spatially dense ionospheric measurement source over the region. A new methodology, based on an adjusted spherical harmonic (ASHA) expansion, was developed to estimate diurnal vertical TEC over the region using GPS observations over the region. The performance of the ASHA methodology to estimate diurnal TEC and satellite and receiver differential clock biases (DCBs) for a single GPS receiver was first tested with simulation data and subsequently applied to observed GPS data. The resulting diurnal TEC profiles estimated from GPS observations compared favourably to measurements from three South African ionosondes and two other GPS-based methodologies for 2006 solstice and equinox dates. The ASHA methodology was applied to calculating diurnal two-dimensional TEC maps from multiple receivers in the South African GPS network. The space physics application of the newly developed methodology was demonstrated by investigating the ionosphere’s behaviour during a severe geomagnetic storm and investigating the long-term ionospheric stability in support of the proposed Square Kilometre Array (SKA) radio astronomy project. The feasibility of employing the newly developed technique in an operational near real-time system for estimating and dissimenating TEC values over Southern Africa using observations from a regional GPS receiver network, was investigated.
3
Carozzi, Tobia. "Radio waves in the ionosphere : Propagation, generation and detection". Doctoral thesis, Uppsala universitet, Institutionen för astronomi och rymdfysik, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1184.
Testo completoAbstract (sommario):
We discuss various topics concerning the propagation, generation, and detec-tionof high-frequency (HF) radio waves in the Earth's ionosphere. With re-gardsto propagation, we derive a full wave Hamiltonian and a polarization evo-lutionequation for electromagnetic waves in a cold, stratified magnetoplasma.With regards to generation, we will be concerned with three experiments con-ducted at the ionosphere- radio wave interaction research facilities at Sura, Rus-siaand Tromsø, Norway. These facilities operate high power HF transmittersthat can inject large amplitude electromagnetic waves into the ionosphere andexcite numerous nonlinear processes. In an experiment conducted at the Surafacility, we were able to measure the full state of polarization of stimulatedelectromagnetic emissions for the first time. It is expected that by using thetechnique developed in this experiment it will be possible to study nonlinearpolarization effects on powerful HF pump waves in magnetoplasmas in the fu-ture.In another experiment conducted at the Sura facility, the pump frequencywas swept automatically allowing rapid, high-resolution measurements of SEEdependence on pump frequency with minimal variations in ionospheric condi-tions.At the Tromsø facility we discovered by chance a highly variable, pumpinduced, HF emission that most probably emanated from pump excited spo-radicE. Regarding detection, we have proposed a set of Stokes parametersgeneralized to three dimension space; and we have used these parameters in aninvention to detect the incoming direction of electromagnetic waves of multiplefrequencies from a single point measurement.
4
Carozzi, Tobia D. "Radio waves in the ionosphere : propagation, generation, and detection /". Uppsala : Institutionen för astronomi och rymdfysik, Univ. [distributör], 2000. http://publications.uu.se/theses/99-3364278-2/.
Testo completo
5
Bond, Giles Edward. "The interaction of radio waves with the auroral ionosphere". Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30629.
Testo completoAbstract (sommario):
A high power radio wave propagating through the ionosphere perturbs the natural plasma in a number of ways. These include bulk changes in the electron temperature and density, and the excitation of plasma waves and instabilities. The ionosphere can be regarded as a natural plasma laboratory, with far greater scale sizes then anything achievable in a conventional laboratory, thus giving unique access to a range of plasma waves and instabilities. In this thesis results from two campaigns involving the EISCAT (European Incoherent SCATter) ionospheric modification facility (heater) at Tromso, Northern Norway are presented. The first campaign, in February 1995, was principally concerned with modification of the auroral electrojet region during both disturbed and quiet conditions. During this campaign the EISCAT UHF incoherent scatter radar was utilised to achieve the first experimental demonstration of artificial inospheric cooling by a high power radio wave. For the second campaign, in April 1996, the most important diagnostic was CUTLASS (Co-operative UK Twin Located Auroral Sounding System), which can measure power backscattered from field aligned irregularities produced during heating. It has been found that irregularities are excited over a horizontal spatial extent of around 175 km, which far exceeds the normal width of the heater beam. The temporal decay of artificial irregularities remain in the ionosphere for up to four minutes after heater-off. In addition to these experimental studies, a computer model has been developed to investigate the electron temperature and density changes which are induced in the ionospheric D- and E-regions during periods of electrojet activity. The model reproduces the experimental observations, and predicts reduced artificial heating efficiency under distributed natural conditions.
6
Stocker, Alan John. "Modification of the ionosphere by means of high power radio waves". Thesis, University of Leicester, 1990. http://hdl.handle.net/2381/35799.
Testo completoAbstract (sommario):
Experiments have been performed at Troms?, Norway and Arecibo, Puerto Rico to investigate the effects produced by high power radio waves (heating) on the high and low latitude ionospheres, respectively. The modifications induced in the F-region have been observed with both incoherent scatter radars and tow power HF diagnostic radio waves. These observations provide information on both heater-induced large scale changes, and small scale density structures. The spatial and temporal development of the perturbation in electron temperature caused by heating, measured at Troms? for the first time, compares well with theory. Observations of thermal striations, which may be the result of the thermal self-focussing of the heater wave, are also presented. The large-scale heater-induced changes in the electron density measured by EISCAT have been compared with those derived from measurements of the phase of reflected HF diagnostic signals. Both methods yield consistent results with regard to whether the electron density is enhanced or depleted but there are, however, differences in the magnitudes of the measured changes. The sign of the perturbation can reveal aeronomical information on the chemical and diffusion characteristics of the unheated ionosphere. The first observations of tow latitude heating by means of low power HF diagnostic waves are presented. The anomalous absorption measured at tow latitudes is less than that at high latitudes, in agreement with theory. The scale length and amplitude of the associated small-scale density structures are comparable at both high and low latitudes. A detailed comparison has been undertaken of the effect of heating at high and low latitudes and the results compared with current theoretical models. The two independent diagnostic techniques (incoherent scatter and low power HF waves) provide a consistent picture of the ionospheric perturbation induced by both heating facilities.
7
Hahlin, Axel. "Coupled waves as a model to describe chaotic turbulence pumped by radio waves in the ionosphere". Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-356265.
Testo completoAbstract (sommario):
Experimental results concerning plasma turbulence pumped in theionosphere by powerful radio waves suggest that the turbulence is due todeterministic chaos. To investigate the possibility of deterministic chaosin the ionosphere coupled wave systems have been studied to see chaoticdynamics. If coupled waves can exhibit chaos it is a possible way tomodel ionospheric chaos. The result showed that chaos was present inboth wave systems studied which means that they could possibly explainthe chaos, to verify this more studies needs to be done on theparameters relevant to the coupled wave systems in the ionosphere andfind if they are in a regime where chaos developsStudier av plasmaturbulens i jonosfären som pumpas av kraftfulla radiovågor antyder att turbulensen är kopplat till deterministiskt kaos. För att undersöka möjligheten för deterministiskt kaos i jonosfären studeras kopplade vågsystem om de kan innehålla kaotiska regimer. Om dessa system visar kaotiskt beteende skulle de kunna användas för att beskriva kaos i jonosfären. Resultatet visade att kaos var närvarande i de kopplade vågsystem som studerats, för att verifiera om de kan användas för att beskriva kaos i jonosfären måste närmare studier av de parametrar som modellen använder sig av göras för att se om de faller inom ett intervall där kaos uppstår.
8
Habarulema, John Bosco. "A contribution to TEC modelling over Southern Africa using GPS data". Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005241.
Testo completoAbstract (sommario):
Modelling ionospheric total electron content (TEC) is an important area of interest for radio wave propagation, geodesy, surveying, the understanding of space weather dynamics and error correction in relation to Global Navigation Satellite Systems (GNNS) applications. With the utilisation of improved ionosonde technology coupled with the use of GNSS, the response of technological systems due to changes in the ionosphere during both quiet and disturbed conditions can be historically inferred. TEC values are usually derived from GNSS measurements using mathematically intensive algorithms. However, the techniques used to estimate these TEC values depend heavily on the availability of near-real time GNSS data, and therefore, are sometimes unable to generate complete datasets. This thesis investigated possibilities for the modelling of TEC values derived from the South African Global Positioning System (GPS)receiver network using linear regression methods and artificial neural networks (NNs). GPS TEC values were derived using the Adjusted Spherical Harmonic Analysis (ASHA) algorithm. Considering TEC and the factors that influence its variability as “dependent and independent variables” respectively, the capabilities of linear regression methods and NNs for TEC modelling were first investigated using a small dataset from two GPS receiver stations. NN and regression models were separately developed and used to reproduce TEC fluctuations at different stations not included in the models’ development. For this purpose, TEC was modelled as a function of diurnal variation, seasonal variation, solar and magnetic activities. Comparative analysis showed that NN models provide predictions of GPS TEC that were an improvement on those predicted by the regression models developed. A separate study to empirically investigate the effects of solar wind on GPS TEC was carried out. Quantitative results indicated that solar wind does not have a significant influence on TEC variability. The final TEC simulation model developed makes use of the NN technique to find the relationship between historical TEC data variations and factors that are known to influence TEC variability (such as solar and magnetic activities, diurnal and seasonal variations and the geographical locations of the respective GPS stations) for the purposes of regional TEC modelling and mapping. The NN technique in conjunction with interpolation and extrapolation methods makes it possible to construct ionospheric TEC maps and to analyse the spatial and temporal TEC behaviour over Southern Africa. For independent validation, modelled TEC values were compared to ionosonde TEC and the International Reference Ionosphere (IRI) generated TEC values during both quiet and disturbed conditions. This thesis provides a comprehensive guide on the development of TEC models for predicting ionospheric variability over the South African region, and forms a significant contribution to ionospheric modelling efforts in Africa.
9
Okoh, Daniel Izuikeninachi. "Developing an ionospheric map for South Africa". Thesis, Rhodes University, 2009. http://hdl.handle.net/10962/d1005244.
Testo completoAbstract (sommario):
This thesis describes the development of an ionospheric map for the South African region using the current available resources. The International Reference Ionosphere (IRI) model, the South African Bottomside Ionospheric Model (SABIM), and measurements from ionosondes in the South African Ionosonde Network, were incorporated into the map. An accurate ionospheric map depicting the foF2 and hmF2 parameters as well as electron density profiles at any location within South Africa is a useful tool for, amongst others, High Frequency (HF) communicators and space weather centers. A major product of the work is software, written in MATLAB, which produces spatial and temporal representations of the South African ionosphere. The map was validated and demonstrated for practical application, since a significant aim of the project was to make the map as applicable as possible. It is hoped that the map will find immense application in HF radio communication industries, research industries, aviation industries, and other industries that make use of Earth-Space systems. A potential user of the map is GrinTek Ewation (GEW) who is currently evaluating it for their purposes
10
Löfås, Henrik. "Ionospheric modification by powerful HF-waves : Underdense F-region heating by X-Mode". Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121898.
Testo completoAbstract (sommario):
Observations of modifications of the electron temperature in the F-region produced by powerful high-frequency waves transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Nevertheless temperature enhancements of the order of 300-400K were obtained. The modifications found can be well described by the theory of Ohmic heating by the pump wave and both temporal and spatial changes are reproduced. A brief overview of several different experimental campaigns at EISCAT facilities in the period from October 2006 to February 2008 are also given pointing out some interesting features from the different experiments. The main focus is then on the campaign during October 2006 and modifications of the electron temperature in the F-region.
11
Moeketsi, Daniel Mojalefa. "Solar cycle effects on GNSS-derived ionospheric total electron content observed over Southern Africa". Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1005275.
Testo completoAbstract (sommario):
The South African Global Navigation Satellite System (GNSS) network of dual frequency receivers provide an opportunity to investigate solar cycle effects on ionospheric Total Electron Content (TEC) over the South Africa region by taking advantage of the dispersive nature of the ionospheric medium. For this task, the global University of New Brunswick Ionospheric Modelling Technique (UNB-IMT) was adopted, modified and applied to compute TEC using data from the southern African GNSS Network. TEC values were compared with CODE International GNSS services TEC predictions and Ionosonde-derived TEC (ITEC) measurements to test and validate the UNB-IMT results over South Africa. It was found that the variation trends of GTEC and ITEC over all stations are in good agreement and show pronounced seasonal variations with high TEC values around equinoxes for a year near solar maximum and less pronounced around solar minimum. Signature TEC depletions and enhanced spikes were prevalently evident around equinoxes, particularly for a year near solar maximum. These observations were investigated and further discussed with an analysis of the midday Disturbance Storm Time (DST) index of geomagnetic activity. The residual GTEC – ITEC corresponding to plasmaspheric electron content and equivalent ionospheric foF2 and total slab thickness parameters were computed and comprehensively discussed. The results verified the use of UNB-IMT as one of the tools for ionospheric research over South Africa. The UNB-IMT algorithm was applied to investigate TEC variability during different epochs of solar cycle 23. The results were investigated and further discussed by analyzing the GOES 8 and 10 satellites X-ray flux (0.1 – 0.8 nm) and SOHO Solar Extreme Ultraviolet Monitor higher resolution data. Comparison of UNB-IMT TEC derived from collocated HRAO and HARB GNSS receivers was undertaken for the solar X17 and X9 flare events, which occurred on day 301, 2003 and day 339, 2006. It was found that there exist considerable TEC differences between the two collocated receivers with some evidence of solar cycle dependence. Furthermore, the daytime UNB TEC compared with the International Reference Ionosphere 2001 predicted TEC found both models to show a good agreement. The UNB-IMT TEC was further applied to investigate the capabilities of geodetic Very Long Baseline Interferometry (VLBI) derived TEC using the Vienna TEC Model for space weather monitoring over HartRAO during the CONT02 and CONT05 campaigns conducted during the years 2002 (near solar maximum) and 005 (near solar minimum). The results verified the use of geodetic VLBI as one of the possible instruments for monitoring space weather impacts on the ionosphere over South Africa.
12
Norin, Lars. "Secondary Electromagnetic Radiation Generated by HF Pumping of the Ionosphere". Doctoral thesis, Uppsala universitet, Astronomi och rymdfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9393.
Testo completoAbstract (sommario):
Electromagnetic waves can be used to transmit information over long distances and are therefore often employed for communication purposes. The electromagnetic waves are reflected off material objects on their paths and interact with the medium through which they propagate. For instance, the plasma in the ionosphere can refract and even reflect radio waves propagating through it. By increasing the power of radio waves injected into the ionosphere, the waves start to modify the plasma, resulting in the generation of a wide range of nonlinear processes, including turbulence, in particular near the reflection region. By systematically varying the injected radio waves in terms of frequency, power, polarisation, duty cycle, inclination, etc. the ionosphere can be used as an outdoor laboratory for investigating fundamental properties of the near-Earth space environment as well as of plasma turbulence. In such ionospheric modification experiments, it has been discovered that the irradiation of the ionosphere by powerful radio waves leads to the formation of plasma density structures and to the emission of secondary electromagnetic radiation, a phenomenon known as stimulated electromagnetic emission. These processes are highly repeatable and have enabled systematic investigations of the nonlinear properties of the ionospheric plasma. In this thesis we investigate features of the plasma density structures and the secondary electromagnetic radiation. In a theoretical study we analyse a certain aspect of the formation of the plasma structures. The transient dynamics of the secondary radiation is investigated experimentally in a series of papers, focussing on the initial stage as well as on the decay. In one of the papers we use the transient dynamics of the secondary radiation to reveal the intimate relation between certain features of the radiation and structures of certain scales. Further, we present measurements of unprecedentedly strong secondary radiation, attributed to stimulated Brillouin scattering, and report measurements of the secondary radiation using a novel technique imposed on the transmitted radio waves.
13
Liu, Haidi. "Radio Frequency Identification (RFID) adoption in the South African retail sector: an investigation of perceptions held by members of the retail sector regarding the adoption constraints". Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1002774.
Testo completoAbstract (sommario):
Radio Frequency Identification (RFID) technology is a ethod of identifying unique items using radio waves that communicate between RFID tags and readers without line-of-sight readability. RFID technology provides great potential in many industries and a wide spectrum of possible uses. Areas of application include person identification, logistics, pharmaceutical, access control, security guard monitoring and asset management. One of the areas where RFID is being used and where it promises excellent results is the retail industry. While RFID systems have the potential to revolutionise the way products and goods are tracked and traced in the retail supply chain, barriers to its widespread adoption exist: for example; technical constraints, return on investment constraints, a lack of awareness and education and as well as privacy and security issues. The research aims to identify the barriers to the adoption of RFID and to investigate the perceptions of RFID held by members of the retail sector in South Africa (SA). Current research and available literature are used to identify RFID adoption barriers and a conceptual framework on this subject is proposed, which is then verified by SA retailers’ perceptions, established by means of a survey. Initial barriers to widespread adoption include a shortage in skills, a lack of standards, high costs associated with RFID devices, the difficulty of integrating with current legacy systems, and a lack of familiarity with the system. Finally, an enhanced framework is proposed, describing RFID adoption barriers within the South African retail sector. In summary, the framework is an outline of the barriers impacting RFID adoption in the SA retail sector that need to be considered and addressed. The framework identifies six categories of RFID adoption barriers, with each category containing two or more barriers relating to that particular category. These categories are Technological, Cost and return on investment, Privacy and security, Implementation, Organisational factors and People.
14
Opperman, B. D. L. "Reconstructing ionospheric TEC over South Africa using signals from a regional GPS network /". 2007. http://eprints.ru.ac.za/1129/.
Testo completo
15
Moeketsi, Daniel Mojalefa. "Solar cycle effects on GNSS-derived ionospheric total electron content observed over Southern Africa /". 2007. http://eprints.ru.ac.za/1155/.
Testo completo
16
Akuon, Peter Odero. "Rain cell size attenuation modelling for terrestrial and satellite radio links". Thesis, 2011. http://hdl.handle.net/10413/8958.
Testo completoAbstract (sommario):
There is need to improve prediction results in rain attenuation in order to achieve reliable wireless
communication systems. Existing models require improvements or we need fresh approaches.
This dissertation presents a model of rain attenuation prediction for terrestrial and satellite radio
links based on a novel approach. This approach postulates that the difference in rain attenuation for
various locations is attributed to the dissimilar rain drop sizes and rain cell diameter sizes and that
cell sizes derived from local measurements would depict the true nature of rain cells better than the
cells derived from long term rain data gathered from different climates. Therefore all other link
parameters used in the attenuation equation are presented by the use of mathematical analysis; but
the rain cell size is derived from local rain rate measurements.
The physical link aspects considered in the mathematical attenuation model are: the Fresnel
ellipsoid of the link path, the effect of elevation angle, the rain cell diameter size and the shape of
growth of rain rates in the cell. The effect of the elevation angle of the link on the scale of
attenuation is accounted for through the proposed coefficient of elevation equation. The coefficient
of elevation is considered to modify the size of the rain cell diameter in proportion to the elevation
angle of the link and the rain rate growth is taken to be of the truncated-Gaussian form. On the
other hand, the rain cell diameter is derived from rain rate measurements as a power law model and
substituted in the attenuation expression.
The rain cell size model evaluated in this dissertation is based on point rain rate measurement data
from the disdrometer located at the University of KwaZulu-Natal, South Africa. The “Synthetic
Storm” technique is applied to develop the rain cell diameter distributions and the rain cell
diameter model. In addition, the impact of the rain cell diameter size model in site diversity and
cellular network-area planning for the region is discussed.
To validate the model for terrestrial links, attenuation data collected from Durban, South Africa is
used while that for satellite links, attenuation data from 15 links which are located in tropical
climatic zones are used. In each case, the new model is tested against some well-known global rain
attenuation prediction models including the standard ITU-R models. The performance of the
proposed models for the sampled radio links based on error estimations shows that improvements
have been achieved and may be regarded as a universal tropical model especially for satellite links.Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.
17
Adetan, Oluwumi. "Modeling of raindrop size distribution and critical diameters for rainfall attenuation over microwave links in Southern Africa". Thesis, 2014. http://hdl.handle.net/10413/11220.
Testo completoAbstract (sommario):
The inability of service providers to constantly meet the design target of 99.99 % availability of the line-of-sight (LOS) microwave links has caused concern among both the operators and consumers. The non-availability of the links is predominantly due to propagation impairments along the propagation link. These propagation effects include cloud, snow, fog, gas attenuation, rain and atmospheric scintillation. Various studies have shown high vulnerability of radio communication systems operating at microwave (3-30 GHz) and millimeter wave (30-300 GHz) to rainfall attenuation especially in the tropical regions characterized by heavy rainfall and relatively large rain drops when compared to the temperate regions. In order to understand the effects of attenuation due to rain on communication systems in any locality (region), a good knowledge of the raindrop size distribution (DSD) and the rainfall rate estimates is necessary for accurate prediction and estimation of the rainfall attenuation.
For this study, experimental raindrop size measurements gathered over a period of three years, using the Joss-Waldvogel RD-80 disdrometer installed at the roof top of the Electrical, Electronic and Computer Engineering building, University of Kwa-Zulu Natal, Durban, a subtropical location in South Africa, is analysed. Disdrometer measurements, sampled at one-minute rate over a period of nine months from Butare, an equatorial site in Rwanda, is also analysed for the purpose of comparison. The estimated R0.01 values for Durban and Butare are employed for the purpose of analysis. Based on the statistical analysis of the measured data samples, DSD parameters are proposed from the negative exponential, modified gamma, Weibull and the lognormal models. The DSD models are compared to models from other countries within and outside the region. The Mie scattering approximation at temperature of 20oC for spherical raindrop shape is adopted for the estimation of the scattering functions. The study further investigates the influence of critical raindrop diameters on the specific rain attenuation for the annual, seasonal and various rainfall regimes in southern Africa. This is achieved analytically by integrating the total rainfall attenuation over all the raindrop sizes and observing the differential change in the attenuation over a given range of drop size diameters. The peak diameter at which the specific rainfall attenuation is maxima is determined for different rainfall regimes. Finally, the cross-polarisation discrimination (XPD) due to rain over Durban is computed at two elevation angles. The results of this study will be helpful for the proper design and allocation of adequate fade margins to achieve the expected quality of service (QoS) in a radio communication system operating in the Southern Africa region.Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2014.
18
Malinga, Senzo Jerome. "Determination of millimetric signal attenuation due to rain using rain rate and raindrop size distribution models for Southern Africa". Thesis, 2014. http://hdl.handle.net/10413/11206.
Testo completoAbstract (sommario):
The advantages offered by Super High Frequency (SHF) and Extremely High Frequency (EHF) bands such as large bandwidth, small antenna size, and easy installation or deployment have motivated the interest of researchers to study those factors that prevent optimum utilization of these bands. Under precipitation conditions, factors such as clouds, hail, fog, snow, ice crystals and rain degrade link performance. Rain fade, however, remains the dominant factor in the signal loss or signal fading over satellite and terrestrial links especially in the tropical and sub-tropical regions within which South Africa falls. At millimetre-wave frequencies the signal wavelength approaches the size of the raindrops, adversely impacting on radio links through signal scattering and absorption. In this work factors that may hinder the effective use of the super high frequency and extremely high frequency bands in the Southern African region are investigated. Rainfall constitutes the most serious impairment to short wavelength signal propagation in the region under study. In order to quantify the degree of impairment that may arise as a result of signal propagation through rain, the raindrops scattering amplitude functions were calculated by assuming the falling raindrops to be oblate spheroidal in shape. A comparison is made between the performance of the models that assume raindrops to be oblate spheroidal and those that assume them to be spherical.
Raindrops sizes are measured using the Joss-Waldvogel RD-80 Distrometer. The study then proposes various expressions for models of raindrops size distributions for four types of rainfall in the Southern Africa region. Rainfall rates in the provinces in South Africa are measured and the result of the cumulative distribution of the rainfall rates is presented. Using the information obtained from the above, an extensive calculation of specific attenuation and phase shift in the region of Southern Africa is carried out. The results obtained are compared with the ITU-R and those obtained from earlier campaigns in the West African sub region. Finally, this work also attempts to determine and characterize the scattering process and micro-physical properties of raindrops for sub-tropical regions like South Africa. Data collected through a raindrop size measurement campaign in Durban is used to compare and validate the developed models.Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2014.