Doctoral Degrees (Land Surveying)
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Item Development of an integrated model and system to enable optimal efficiency of the HartRAO LLR signal path.(2017) Ndlovu, Sphumelele Colin.; Combrinck, Ludwig.; Akombelwa, Mulemwa.; Chetty, Naven.The Lunar Laser Ranger (LLR) system under development at the Hartebeesthoek Radio Astronomy Observatory (Hartford) in South Africa is being built to accurately measure the Earth-Moon distance (at 1 cm level) through the use of short laser pulses, a single photon detection system, an accurate timing system and other sophisticated components. This LLR system is unique in Africa and indeed in the entire Southern Hemisphere. The system utilizes a 1 m diameter optical telescope, which was donated to the project by the Observatoire de la Côte d’Azur of France. In this work, the author discusses the development of an integrated model that will be utilized to obtain optimal efficiency of the HartRAO-LLR system. The model is used to estimate the expected number of returned photons by considering a number of parameters which affects the laser beam pulses as they traverse the atmosphere from the LLR telescope to the Moon and back to the telescope. Factors such as the apparent Earth-Moon range, atmospheric extinction, laser beam characteristics, optical path efficiencies and others, affect the estimated (predicted by software) and actual (measured) number of returned photons for the HartRAO-LLR station. The estimated average signal return rate (which is dependent on a number of factors) of the HartRAO-LLR ranges between 0 to 12 photons per minute, which is in agreement with the available data from five globally distributed LLR stations. It also correlated with the estimated returns that were obtained using least squares parameter estimations. They were in agreement by an average difference of 0.00272. Our estimated signal returns are strongly affected by two-way atmospheric extinction (atmospheric and cirrus cloud transmissions), variations in the laser beam incident angle on the retroreflectors located on the Moon as well as the varying Earth-Moon range. A new parameter, named lunar reflectivity ranging between 0 and 1, was introduced in the link budget equation to consider the effects of Moon Phases on the returned photons. Modelling the returned number of photons and comparing these to the actual number received leads to an understanding of the effects of numerous variables on the total laser path efficiency. Total system efficiency can be improved as well, as particular atmospheric conditions will not allow LLR to be successful on certain days. For these days, the system can be utilized for other purposes such as maintenance or satellite laser ranging.Item Evaluating cadastral systems in periods of uncertainty: a study of Cape Town's Xhosa-speaking communities.(1999) Barry, Michael Brendan.; Fourie, Clarissa.Evaluating the effectiveness of a cadastral system in situations where the social, political and economic environments are volatile and there is uncertainty over whether the cadastral system is likely to be used in the manner intended by the authorities remains a priority in developing countries. South African society, having negotiated a new democratic political dispensation in the early 1990’s, has been experiencing fundamental social and political change. In this context, the experimental focus of this study is on analysing effective cadastral system usage by people who were previously excluded from owning land in urban areas. The study explores the effectiveness of the existing cadastral system in addressing the wants of Xhosa-speaking communities in Cape Town during this period of substantial change. There is a paucity of substantive and methodological theory to evaluate a cadastral system in an uncertain, unstable situation. Based on soft systems theory, strategic management theory and existing cadastral theory, a conceptual framework to understand a particular situation has been developed. Using this conceptual framework, and drawing on the theory of planned behaviour and a social change model, an evaluative framework has been created that is germane to the South African situation. The primary focus of the empirical work in this study was on usage of the system of cadastral boundaries and the land registration system. A set of four case studies that includes an informal settlement, two site-and service schemes and a suburb where much of the land is held in private ownership were studied. These case studies were augmented by a study of a large area that is predominantly Xhosa-speaking in Cape Town’s eastern metropole. The conceptual and evaluative frameworks and the methodology adopted to conduct this research were found to constitute valid substantive and methodological theoretical foundations for studies of cadastral systems and land administration systems. In the context of the empirical work conducted, it is concluded that in Cape Town’s Xhosa speaking communities, in a stable situation where a favourable environment encourages its usage, the existing cadastral system will be effective and used in the manner intended by government. In volatile, unstable situations, the cadastral system will not be fully utilised for a variety of reasons. One reason being that in a rapidly changing social and political environment the land administration authority may not be able to govern effectively, and at the same time factions within a settlement may manipulate the land tenure rules to suit their own objectives. In such situations, conflict is inherent and natural in the relationship between the authorities and the community within a particular settlement and in the relationship between factions within that community. However, in this study it was found that in these uncertain situations that although cadastral instruments and processes were not used to effect all transactions in land, they form the essential core of a range of systems that are used to affirm an individual’s claims to rights in land. Moreover, in cases of conflict over land rights, the official records and surveyed cadastral boundaries constituted the point of departure in all negotiations.Item Seismic sources, seismotectonics and earthquake recurrence for the KZN coastal regions.(2016) Singh, Mayshree.; Akombelwa, Mulemwa.; Maud, Rodney.Historical earthquake information forms a critical dataset for seismotectonic investigations that can be used for seismic hazard investigations of hazardous and high rise structures and national seismic hazard maps. This study systematically interrogates historical earthquake data for the region from various sources in order to have a better understanding of the origins of the larger earthquakes. Several previously undocumented earthquakes were found that can supplement the national catalogue. Various sources are postulated as origins of these tremors namely local sources located in Mtubatuba and offshore sources like the Mozambique Channel. A seismotectonic model of the study region is also presented from an analysis of earthquake data, structural and kinematic systems. Geo-spatial data from geology, tectonics, regional geophysical anomalies, historical and instrumental seismicity and kinematics are considered. For what was once considered as a diffuse seismotectonic region with low levels of seismicity and where insufficient, uncertain and incomplete data existed – we now have datasets that are more complete and have higher levels of accuracy. Earthquake epicentres from both the historical and instrumental record as well as thermal spring localities correlate with old Jurassic faults. An assembly of a variety of datasets and studies are performed followed by a delineation of respective seismotectonic provinces. Earthquake recurrence parameters were assessed for the seismic provinces. Many of the provinces had insufficient seismic data to compute parameters. Improved seismic monitoring of the east coast region is required to better characterise the seismic risk. These results re-emphasize the need to better understand the coastal environment for seismotectonic characterization and to densify the seismic network towards the eastern coastline.