3. Electronic Theses and Dissertations (ETDs) - All submissions
Permanent URI for this communityhttps://wiredspace.wits.ac.za/handle/10539/45
Browse
3 results
Search Results
Item The Southward spread of Johannesburg and its impact on precolonial stone walled structures(2018) Naidu, Saireeni LatishaThere are thousands of Stone Walled Structures (SWS) located in the southern half of the Gauteng Province. In the absence of relevant historical documents, these SWS are all the information we have about how pre-colonial societies were organized in this area. Unfortunately, they are threatened by rapid urbanization and development. This research attempts to estimate how many Iron Age SWS have been lost to urban development in Johannesburg South during the last 80 years. I mapped and quantified the SWS and urbanization in four chronological snapshots using remote sensing techniques. Aerial photographs from 1937 and 1961 were used as well as Google Earth satellite images from 2005 and 2015. The data was analyzed on the ESRI software ArcGIS 10.3. The four snapshots show the trend in urban sprawl and destruction of SWS and this information is valuable for mitigation strategies. Fortunately, there are legislations and procedures in place to ensure that not all these sites are lost forever.Item Land degradation in the Limpopo Province, South Africa(2007-02-26T13:25:10Z) Gibson, Donald J. D.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.Item The applicability of remote sensing methods for the detection of fires on coal discard dumps(2006-11-17T08:56:25Z) Mistry, PratibhaThis report investigates the viability of satellite remote sensing in monitoring the rehabilitation of coal discard dumps. Four levels of thermal monitoring data were assessed in this project. These were: ground and below surface temperature probes; aerial thermal and atmospheric monitoring surveys; high altitude aircraft; and satellites. Remote sensing methods measure only variation of temperatures on the surface of the dump. Fires on discard dumps are sub-surface fires, and the depth and extent of the fire below the surface cannot be easily inferred. The resolution of satellite sensors is a limiting factor for detecting individual hotspots on dumps. Small mine dumps occupy just a few pixels and the position of fires cannot be accurately assessed. Although the larger dumps are discernable, the variation of temperatures across the dump cannot be easily determined. For the present, aircraft monitoring may be the most viable means of monitoring spontaneous combustion in coal discard dumps, until satellite resolutions improve further.