Land Surveying

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Change detection of invasive bracken fern (Pteridium aquilinum [L.] Kuhn) in the Royal Natal National Park and Rugged Glen Nature Reserve.
(2013) Singh, Kaveer.; Forbes, Angus Mcfarlane.; Akombelwa, Mulemwa.
Bracken fern (Pteridium aquilinum [L.] Kuhn) is an indigenous invasive plant and it is known to have a negative impact on biodiversity. This research focuses on infestations of bracken fern in two areas within the uKhahlamba Drakensberg Park World Heritage Site; the Royal Natal National Park and the Rugged Glen Nature Reserve. Prior change detection research on bracken fern were constrained due to the low resolution satellite imagery and the inability of hard classification techniques to account for the mixtures of land cover types that occur within pixels of low resolution imagery. To overcome these constraints this research applied the fuzzy image classification technique to multispectral digital aerial imagery of 0.5 m spatial resolution. Multi date imagery used for image classification was captured in the mid-winter of 2009 and mid-spring of 2011. Thereafter post-classification change detection analysis was conducted using the fuzzy classified images. The classified images were verified using ground truth surveys. The 2009 and 2011 fuzzy classified images produced overall accuracies of 81.4% and 94.4% with Kappa coefficients of 0.63 and 0.89 respectively. This research found that the distinct seasonal development pattern of bracken fern and the time of year imagery were captured were significant factors in its detection. As bracken fern was found to be more spectrally distinct in spring as compared to winter, due to the plant growth of bracken fern, grass and other shrubbery. These classified images were used in post-classification change detection analysis which revealed that the bracken fern infestation in the Royal Natal National Park and Rugged Glen Nature Reserve had increased at a rate of 24 % and 27 % per annum respectively. This showed that bracken fern is spreading in the Royal Natal National Park and Rugged Glen Nature Reserve, as expected. Fire regimes, slope and aspect were found as factors that could be promoting the spread of bracken fern, 67.5 % and 75 % of the bracken fern infestation in the Park and Reserve respectively, occurred in areas that were burnt by fire regimes and have gentle to moderately gentle slopes facing east, south east and south.
Characterization and development of optical components for the Cassegrain telescope and laser beam coudé path of the lunar laser ranger of HartRAO.
(2015) Nkosi, Nokwazi Purity.; Combrinck, Ludwig.; Akombelwa, Mulemwa.
The Observatoire de la Côte d’Azur (OCA) donated a 1-m Cassegrain telescope to be used for the dual satellite and lunar laser ranging system currently under development at the Hartebeesthoek Radio Astronomy in South Africa. As the very first of its kind in the Southern Hemisphere, the new system will be designed and developed as a permanent lunar laser ranging system with high precision laser and electronic equipment to achieve millimetre accuracy. Limited technical details of the telescope exist so tests were conducted to determine the optical characteristics and performance of the telescope and its mirrors. The optical performance of the telescope was validated through the analysis of transmission efficiency, structural efficiency and image quality. Spectroscopic measurements were conducted to determine the transmission efficiency of the telescope by taking into account all losses in light from the reflection of mirrors, transmission of lenses and the secondary spider central obstruction along the path of the proposed coudé optical path. A system transmission of ∼90% was obtained if a coudé path with no central obstruction is used. The primary mirror and its support structure was validated using finite element analysis software (ANSYS) to model the amount of deformation the mirror will experience under gravitational and external loading. Taking into account the lightweight nature (honeycomb structure) of the mirror, its material properties and multiple support mechanism, ANSYS was used to compute the gravity deformations experienced by the mirror as the telescope tracks from the horizon to zenith. The deformations when gravity acts along the axial support were in the range of 1/6th of the wavelength, which is below the maximum limit expected for such a structure at the given weight. In order to analyse the image quality of the system, an optical analysis software (OSLO) was used. Spot diagram analysis revealed coma as the dominant primary aberration in the system. The telescope is diffraction-limited for on-axis performance and yields a Strehl ratio of 0.78 for off-axis performance.
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.
Evaluation of largis application in planning, acquisition and maintenance of utility servitudes : an Eskom case study.
(2016) Monamane, Ntombizodwa A.; Chilufya, Sexton Mwitwa.; Musonda, E.; Akombelwa, Mulemwa.
GIS has been used for quite some time by utility organisations while the demands for their services by the public have also increased exponentially. This has prompted many utility organisations to constantly review their systems in operation for any potential problems associated with their use in order to propose possible and suitable improvements necessary to maximize their production. This study evaluates the performance of Land and Rights Geographic Information System (LARGIS), a GIS based information management system employed by Eskom to manage its servitudes’ land rights information. LARGIS has been analysed in terms of its application to planning, acquisition, registration and maintenance of servitudes land rights information. Information on LARGIS was collected using a questionnaire administered to Eskom personnel that work with the system while interviews were used to obtain more information not obtainable from the questionnaire. Obtained information was analysed using a relational matrix of data sets and processes in order to identify subsystems making up LARGIS. Information flows and processes in each of the subsystems were then analysed using Data Flow Diagrams (DFD) supported by associated Data Dictionary (DD) so as to identify possible shortcomings in information flows and information processing. The information collected was also used to identify institutional, legal, economic and additional technical shortcomings. The study revealed that LARGIS had made a positive impact on the way Eskom previously managed its servitudes by using a single system to plan, acquire, register and maintain land rights associated with servitudes. However, the study also identified shortcomings for which recommendation have been proposed so as to make LARGIS much more responsive to Eskom`s demands for servitudes land rights information management.
Exploring the spatial expansion of settlements in customary regions : a case study of Adams rural, KwaZulu-Natal.
(2015) Dlamini, Siboniso Msinsi.; Akombelwa, Mulemwa.; Chilufya, Sexton Mwitwa.
Adams Rural is one of KwaZulu-Natal’s customary regions which falls under the traditional boundaries of the Ingonyama Trust Board. In this rural area traditional customs are still being practiced. The major land use was previously dominated by agriculture and very few residential settlements. This study reflects on the increasing recognition of the expansion of human settlements in this customary region. The expansion of human settlements is observed to have increased over the past decade and is confirmed by annual aerial imagery of the area captured by the eThekwini Municipality. The historical images captured by the National Geo-Spatial Information (NGI) suggest that there has been a substantial land use change in the area, resulting in loss of land previously used for sugarcane plantation. Therefore the study utilised spatial analytic techniques to quantify spatial changes in Adams Rural and map the land use / land cover change between years 2001-2004, 2004-2006, 2006-2008, 2008-2010 and 2010-2012 in Adams Rural. The research employs a post-classification change detection technique performed on selected orthophoto imagery, to assess spatial change patterns, to quantify the amount and the rate of change in human settlements of Adams Rural during the period 2001 to 2012. The results show that spatial extent of human settlements has more than doubled with commensurate loss in agriculture. Demographic data for 2001 and 2011 obtained from Statistics South Africa (Statistics SA, 2001 and 2011) also confirms that the population of the area has more than doubled over the same period. The rate of increase in settlements varied between periods considered with the population increasing proportionately. A closer inspection of the area was conducted using a questionnaire administered to the community. The questionnaire shows that the major contributor to the population increase in the area is the majority of people relocating from urban areas to this customary region. The questionnaire results further show that people are attracted to the development occurring in the area, larger parcels extent and the low cost of living with no bond payments, as there are no property rates payable on customary land. An attempt was made to project the spatial growth of built-up areas over the next 10 years using the change rate obtained from change detection verifying the prediction using the results from a questionnaire survey of the residents in the study area. It is observed that change by 2022 may likely follow the trend in 2001-2012. The present study shows that spatial analysis based on land use mapping using orthophoto imagery is very effective in monitoring the spatial features in customary regions.
Investigating the feasibility of establishing a South African marine cadastre.
(2015) Reddy, Kovilen.; Akombelwa, Mulemwa.; Chilufya, Sexton Mwitwa.
Human interaction with the marine environment is increasing at a rate at which marine management systems cannot keep pace. The land cadastral systems are deemed to be well-established and understood thanks to hundreds of years of development. Meanwhile, as marine technological innovations advance and population density in coastal areas grows, human interaction with the oceans is evolving, making existing systems in place for their management seem out-dated. In South Africa, the declaration of Project Phakisa to unlock the oceans economy, which has been relatively untouched, acknowledges the potential benefits that can be extracted from the sea. A land cadastral system consists of graphically depicted boundaries that have been surveyed, and a register that assigns any rights, restrictions and responsibilities to the area enclosed by such surveyed boundaries. Management of marine property rights is not dissimilar to the land cadastre insofar as there being parallel survey and registry components. Internationally, marine cadastre initiatives are being researched and implemented to update marine management systems while there is recognition for convergence of land and sea based spatial data infrastructures. This study explores the need for the development of a seamless cadastre across the land-sea interface for South Africa by assessing the perceptions of stakeholders that deal in land and/or marine environments. The study investigates access to land versus marine spatial data, legal and technical aspects, components and features of a possible marine cadastre. By adopting a case study strategy using both qualitative and quantitative inquiry approaches, the rendered results presented later in the dissertation have increased reliability resulting from the processes of data triangulation. The main findings indicate that the spatial and accompanying registration component of the land-based cadastral system is sufficient to form the cornerstone of land administration in SA. The literature review and canvassing of persons related to the geospatial fraternity indicates, via analysis of a questionnaire and interviews, shortcomings in good ocean governance. Although a marine cadastral system is feasible for SA, it is beset with spatial, technical, legislative and institutional issues that need ironing out. The unification of the land and possible marine cadastral systems would enable a single land-sea spatial data infrastructure that would mute the effects of an uncertain land-sea interface.
Seismic risk evaluation for the eThekwini Municipality Area.
(2015) Ramirez, Jennifer Eliana Martinez.; Singh, Moganavelli.; Akombelwa, Mulemwa.; Chilufya, Sexton Mwitwa.
Abstract available in PDF file.
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.

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