Browsing by Author "Van Niekerk, Adriaan"

Now showing 1 - 20 of 43
  • No Thumbnail Available
    Item
  • No Thumbnail Available
    Item
    A GIS database of tourism infrastructure in the Western Cape Province
    (2007) Van der Merwe JH; Ferreira SLA; Van Niekerk, Adriaan
  • No Thumbnail Available
    Item
  • Thumbnail Image
    Item
    Advances in optical earth observation for geological mapping : a Review
    (CONSAS Conference, 2016) Ngcofe, Luncedo Dalithemba; Van Niekerk, Adriaan
    Recent increases in the availability of earth observation (EO) data and the advances made in its processing have opened up new opportunities for earth monitoring studies. This article reviews recent advances in EO, specifically in the optical domain, and comments on their potential for geological investigations. A review of the literature revealed that much work has been done on the use of multispectral to hyperspectral EO data for geological investigations, but that relatively little emphasis has been placed on the value of high spatial resolution in geological studies. From the literature it was found that geographic object based image analysis (GEOBIA) is a relatively new paradigm in remote sensing that has been shown to reduce the intra-class spectral variability in high spatial resolution imagery, thereby increasing image classification accuracies. It has been used for many applications, but relatively little research has been done on the application of GEOBIA for geological investigations. Another finding of this review is that the power of EO data increases substantially when different types of data are used (fused) together. Data fusion seizes the advantages of the capabilities of each sensor while reducing its limitations. By its nature, GEOBIA offers the ability to fuse disparate data sources and the review concludes that more research is required on the use of GEOBIA and data fusion of high resolution EO data for geological mapping.
  • No Thumbnail Available
    Item
    Ants, altitude and change in the northern Cape Floristic Region
    (Blackwell publishing Ltd, 2006) Botes, A.; McGeoch, M. A.; Robertson, H. G.; Van Niekerk, Adriaan; Davids, H. P.; Chown, S. L.; 0000-0002-5631-0206
    Aim: Climate-modelling exercises have demonstrated that the Cape Floristic Region is highly sensitive to climate change and will apparently lose much of its northern limits over the next few decades. Because there is little monitoring of diversity in this area, ant assemblage structure was investigated within the main vegetation types in the Greater Cederberg Biodiversity Corridor. In particular, we sought to determine how ant assemblage structure differs between the main vegetation types, how restricted ants – and in particular the major myrmecochores – are to the major vegetation types, and which environmental variables might underlie differences in the ant assemblages and in the specificity of species to particular areas. Location: Northern Cape Floristic Region, Western Cape, South Africa. Methods: Sampling was undertaken during October 2002 and March 2003 across an altitudinal gradient ranging from sea level (Lambert’s Bay) to c. 2000 m a.s.l. (Sneeukop, Cederberg) and down again to 500 m a.s.l. (Wupperthal) in the Western Cape, South Africa. Pitfall traps were used to sample ants at 17 altitudinal bands, stretching over three vegetation types (Strandveld, Mountain Fynbos and Succulent Karoo). Biotic and abiotic environmental variables were collected at each sampling site. Generalized linear models were used to determine the relationships between species richness, density, abundance and the abundance of the major myrmecochores, and the environmental variables. Redundancy analysis was used to determine the relationship between ant assemblage structure and the environmental variables. The Indicator Value Method was used to identify characteristic ant species for each vegetation type and altitudinal site. Results: Temperature explained significant proportions of the variation in species density and abundance, and, together with area and several vegetation variables, contributed significantly to the separation of the assemblages in the major vegetation types and biomes. Four major myrmecochores were identified [Anoplolepis sp. (cf. custodiens), Anoplolepis sp. (cf. steinergroeveri), Camponotus niveosetosus, Tetramorium quadrispinosum]. The abundances of the two Anoplolepis species were related to vegetation variables, while the abundance of the other two species showed opposite relationships with temperature variables. Fourteen ant species were characteristic of certain vegetation types and altitudes. Several of these species contributed to the differences between the assemblages. Main conclusions: There are likely to be substantial and complex changes to ant assemblages as climates change in the northern Cape Floristic Region. Moreover, the importance of ants for ecosystem functioning suggests that these responses are not only likely to be a response solely to vegetation changes, but might also precipitate vegetation changes. The changes that are predicted to take place in the next 50 years in the Cape Floristic Region could be substantially exacerbated by such synergistic effects, which have major implications for long-term conservation plans. Ongoing monitoring of this transect will reveal the nature and pace of the change as it unfolds.
  • Thumbnail Image
    Item
    Application of geospatial technology for gap analysis in tourism planning for the Western Cape
    (Academy of Science of South Africa, 2013) Van der Merwe, Johannes H.; Van Niekerk, Adriaan
    ENGLISH ABSTRACT: We report on the use of modern spatial computing technology in the development of spatial tourism policy and planning in the context of a bounded resource base. We refer briefly to provincial tourism development policy, expand on the tourism marketing framework and use the express tourist preferences to determine suitability indicators or attraction features for a spatial tourism resource base, paying special attention to the conceptual foundations of attraction and the mapping of tourism potential variables. We applied the methodology to a combination of tourism products in the Western Cape Province of South Africa in an approach that involved applying the spatial multiple criteria evaluation through the weighted linear combination of spatial factor layers as images in a geographical information system. We performed an analysis of the gap between tourism potential and tourism resource provision at a spatial resolution of individual towns’ spheres of influence, as represented by Thiessen polygons. The outcome in map format demonstrates the applicability of the technique to the Western Cape. The fine-scale spatial result was analysed for its strategic planning implications. Our results are useful for entrepreneurial and regulatory planning and can be replicated in different spatial locations if the appropriate database can be constructed.
  • Thumbnail Image
    Item
    Assessing the influence of DEM source on derived streamline and catchment boundary accuracy
    (South African Water Research Commission, 2019) Mashimbye, Zama Eric; De Clercq, Willem Petrus; Van Niekerk, Adriaan
    Accurate DEM-derived streamlines and catchment boundaries are essential for hydrological modelling. Due to the popularity of hydrological parameters derived mainly from free DEMs, it is essential to investigate the accuracy of these parameters. This study compared the spatial accuracy of streamlines and catchment boundaries derived from available digital elevation models in South Africa. Two versions of Stellenbosch University DEMs (SUDEM5 and DEMSA2), the second version of the 30 m advanced spaceborne thermal emission and reflection radiometer global digital elevation model (ASTER GDEM2), the 30 and 90 m shuttle radar topography mission (SRTM30 and SRTM90 DEM), and the 90 m Water Research Commission DEM (WRC DEM) were considered. As a reference, a 1 m GEOEYE DEM was generated from GeoEye stereo images. Catchment boundaries and streamlines were extracted from the DEMs using the Arc Hydro module. A reference catchment boundary was generated from the GEOEYE DEM and verified during field visits. Reference streamlines were digitised at a scale of 1:10 000 from the 1 m orthorectified GeoEye images. Visual inspection, as well as quantitative measures such as correctness index, mean absolute error, root mean squares error and figure of merit index were used to validate the results. The study affirmed that high resolution (<30 m) DEMs produce more accurate parameters and that DEM source and resampling techniques also play a role. However, if high resolution DEMs are not available, the 30 m SRTM DEM is recommended as its vertical accuracy was relatively high and the quality of the streamlines and catchment boundary was good. In addition, it was found that the novel Euclidean distance-based MAE and RMSE proposed in this study to compare reference and DEM-extracted raster datasets of different resolutions is a more reliable indicator of geometrical accuracy than the correctness and figure of merit indices.
  • No Thumbnail Available
    Item
  • No Thumbnail Available
    Item
    Biomass estimation using satellite imagery
    (2011) Van Niekerk, Adriaan; Stephenson GR
  • No Thumbnail Available
    Item
    Climate and the evolution of group-living behaviour in the armadillo lizard (Ouroborus cataphractus)
    (ZOOLOGICAL SOC SOUTHERN AFRICA, AFRICAN ZOOLOGY CIRCULATION OFFICE, PO BOX11663,, PRETORIA, SOUTH AFRICA,0028, 2013) Shuttleworth C; Mouton PLN; Van Niekerk, Adriaan
  • Thumbnail Image
    Item
    CLUES : a web-based land use expert system for the Western Cape
    (Stellenbosch : Stellenbosch University, 2008-12) Van Niekerk, Adriaan; Van der Merwe, J. H.; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies.
    GIS has revolutionized geographic analysis and spatial decision support and has greatly enhanced our understanding of the real world though it’s mapping and spatial modelling capabilities. Although GIS software is becoming more powerful, less expensive and more userfriendly, GIS still remains the domain of a selected few who can operate and afford these systems. Since the introduction of web mapping tools such as Google Earth, accessibility to geographic information has escalated. Such tools enable anyone with access to a computer and the Internet to explore geographic data online and produce maps on demand. Web mapping products have, however, a very narrow range of functionality. In contrast to GIS that focuses on spatial data capture, storage, manipulation, analysis and presentation, the function of web mapping tools is to visualize and communicate geographical data. The positive impact of web mapping tools suggests, however, that GIS has not yet developed to a level where anyone can use the technology to support spatial decisions and enhance productivity. A possible solution is to close the functional gap between web mapping tools and GIS to make spatial analysis more accessible, thereby promoting geographical awareness and supporting better spatial decisions.
  • Thumbnail Image
    Item
    A comparison of geographical information science competency requirements
    (CONSAS Conference, 2013) Du Plessis, Heindrich; Van Niekerk, Adriaan
    Because universities often provide training in geographical information science (GISc) as part of geography, surveying as well as environmental and computer science programmes, the content, outcomes, extent and quality of training can vary significantly. Very little research has been done on how the existing sets of competency requirements for GISc overlap or differ. No literature exists that identifies commonalities and inconsistencies (gaps) at detail level that could assist with developing a framework that incorporates both South African and international GISc curricula guidelines. Three sets of competency guidelines, namely the U.S.-developed Geographic Information Science and Technology (GI S&T) Body of Knowledge (BoK) developed by the University Consortium for Geographic Information Science (UCGIS), the South African Unit Standards-Based Qualifications (USBQ) and the South African Council for Professional and Technical Surveyors (PLATO) model, are compared qualitatively and quantitatively to identify commonalities and inconsistencies. The exercise identified duplication among the three models and highlighted themes that the South African GISc community deems to be important. The study further identifies topics in the GI S&T BoK that the GISc community in the U.S. considers to be essential knowledge for anyone wishing to practice in the GISc field. The BoK offers the most comprehensive and detailed set of GI competencies, but lacks generic competencies such as physics. Some competencies are unique to a specific set, for example physics and geographical science in the PLATO model, while training is unique to the USBQ. The authors conclude that a new competency set based on the findings of the research is needed to best serve the GISc industry and academia. Recommendations for further research are made.
  • Thumbnail Image
    Item
    A comparison of land unit delineation techniques for land evaluation in the Western Cape, South Africa
    (Elsevier, 2010-07) Van Niekerk, Adriaan; 0000-0002-5631-0206
    Land evaluation, an integral part of land use planning, has been established as one of the preferred methods to support sustainable land use management. In essence, land evaluation aims to compare and match each potential land use with the properties of individual parcels of land, also called land units. A land unit is an area that is, according to predetermined properties, different from the surrounding land and can be assumed to have homogeneous land properties (e.g. climate, soils, cover). Land components (also called landform elements, terrain units or land surface segments) are often used as land units, mainly because their boundaries frequently coincide with transitions in environmental conditions. Although land components have traditionally been delineated by studying topographical maps, interpreting aerial photographs and making field measurements, such manual mapping techniques are very time-consuming and subjective. Land component maps can be generated more objectively and faster by using computer algorithms. This paper compares the maps produced by three algorithms, namely the automated land component mapper (ALCoM), the iterative self-organizing data analysis technique algorithm (ISODATA) and multi-resolution image segmentation (MRS), to determine which technique produces the most homogenous and morphologically representative land components for an area in the Western Cape province of South Africa. The results revealed that the three methods produced significantly different land component maps. While ISODATA's units were relatively homogenous, their boundaries rarely followed morphological discontinuities. ALCoM performed better in delineating land components along terrain discontinuities, but produced relatively heterogeneous land components. Overall, MRS performed consistently well and was significantly more sensitive to morphological discontinuities than the other two methods tested. Land use managers should, however, use MRS with care as more research is needed to determine what effect its different input parameters have on land unit boundaries.
  • Thumbnail Image
    Item
    Development of a composite soil degradation assessment index for cocoa agroecosystems in southwestern Nigeria
    (European Geosciences Union, 2017-08-09) Adeniyi, Sunday Adenrele; De Clercq, Willem Petrus; Van Niekerk, Adriaan
    Cocoa agroecosystems are a major land-use type in the tropical rainforest belt of West Africa, reportedly associated with several ecological changes, including soil degradation. This study aims to develop a composite soil degradation assessment index (CSDI) for determining the degradation level of cocoa soils under smallholder agroecosystems of southwestern Nigeria. Plots where natural forests have been converted to cocoa agroecosystems of ages 1–10, 11–40, and 41–80 years, respectively representing young cocoa plantations (YCPs), mature cocoa plantations (MCPs), and senescent cocoa plantations (SCPs), were identified to represent the biological cycle of the cocoa tree. Soil samples were collected at a depth of 0 to 20 cm in each plot and analysed in terms of their physical, chemical, and biological properties. Factor analysis of soil data revealed four major interacting soil degradation processes: decline in soil nutrients, loss of soil organic matter, increase in soil acidity, and the breakdown of soil textural characteristics over time. These processes were represented by eight soil properties (extractable zinc, silt, soil organic matter (SOM), cation exchange capacity (CEC), available phosphorus, total porosity, pH, and clay content). These soil properties were subjected to forward stepwise discriminant analysis (STEPDA), and the result showed that four soil properties (extractable zinc, cation exchange capacity, SOM, and clay content) are the most useful in separating the studied soils into YCP, MCP, and SCP. In this way, we have sufficiently eliminated redundancy in the final selection of soil degradation indicators. Based on these four soil parameters, a CSDI was developed and used to classify selected cocoa soils into three different classes of degradation. The results revealed that 65 % of the selected cocoa farms are moderately degraded, while 18 % have a high degradation status. The numerical value of the CSDI as an objective index of soil degradation under cocoa agroecosystems was statistically validated. The results of this study reveal that soil management should promote activities that help to increase organic matter and reduce Zn deficiency over the cocoa growth cycle. Finally, the newly developed CSDI can provide an early warning of soil degradation processes and help farmers and extension officers to implement rehabilitation practices on degraded cocoa soils.
  • No Thumbnail Available
    Item
    Die ontwikkeling van geografiese inligtingstelsels vir omgewingsbestuur in die Wes-Kaap
    (Stellenbosch : Stellenbosch University, 1996) Van Niekerk, Adriaan; Stellenbosch University. Faculty of . Dept. of .
  • Thumbnail Image
    Item
    Effect of feature dimensionality on object-based land cover classification : a comparison of three classifiers
    (CONSAS Conference, 2013) Myburgh, Gerhard; Van Niekerk, Adriaan
    The efficient mapping of land cover from remotely sensed data is highly desirable as land cover information is essential for a range of environmental and socio-economic applications. Supervised classifiers are often applied in remote sensing to extract land cover information. While spectral information is typically used as the main discriminating features for such classifiers, additional features such as vegetation indices, transformed spectral data, textural information, contextual information and ancillary data may also considerably influence the accuracy of classification. Geographic object-based image analysis (GEOBIA) allows the easy integration of such additional features into the classification process. This paper compares the performance of three supervised classifiers in a GEOBIA environment as an increasing number of object features are included as classification input. Classification tree analysis (CTA) was employed for feature selection and importance ranking. Object features were considered in the order of their obtained rank. The support vector machine (SVM) produced superior classification accuracies when compared to those of nearest neighbour (NN) and maximum likelihood (ML) classifiers. Both SVM and NN produced stable results as the feature-set size was increased towards the maximum (22 features). ML’s performance, however, decreased considerably when few training samples are used and when the feature-set size (dimensionality) is increased.
  • No Thumbnail Available
    Item
    Evolution of flora and vegetation in saline habitats of South Africa
    (2007) Mucina L; Jurenka R; Steffen S; Van Niekerk, Adriaan
  • Thumbnail Image
    Item
    Game, fences and motor vehicle accidents : spatial patterns in the Eastern Cape
    (South African Wildlife Management Association, 2005-10) Eloff, P. J.; Van Niekerk, Adriaan; 0000-0002-5631-0206
    In South Africa, very little research on motor vehicle accidents involving animals has been done. Transport networks expand while traffic volumes and speed increases. Animals entering the road reserve pose dangers to vehicles. In the Eastern Cape, the presence of an abundance of kudu creates hazardous driving conditions for motorists. For collision prevention and the establishment of public awareness programmes, it is imperative to identify hazardous sections. In this study road traffic collision reports of a chosen route in the Eastern Cape were analysed. It was determined that the presence of long stretches of game proof fences partially clustered the spatial distribution of collision sites. Road trajectories with few or no game proof fences displayed a random distribution of collision sites. “Hotspots” were identified on which traffic authorities can focus mitigating and preventative measures.
  • Thumbnail Image
    Item
    Growth potential study 2014
    (Western Cape Government, 2014-03) Van Niekerk, Adriaan; Du Plessis, Danie; Spocter, Manfred; Ferreira, Sanette; Dondaldson, Ronnie; Loots, Lieb; Boonzaaier, Ilze; Janeke, Dudley; Terhoven, Quinton
    This study determined the growth potential and socio-economic needs of settlements in the Western Cape outside of the Cape Town metropolitan area using quantitative data (e.g. factors relating to socio-economic, economic, physical-environmental, infrastructure and institutional aspects). The results of the quantitative analyses were combined with qualitative information (e.g. stakeholder engagements) to identify potential interventions that might unlock latent potential within settlements and regions.
  • No Thumbnail Available
    Item
    Habitat-level Classification of the Albany Coastal, Pondoland Scarp and Eastern Scarp Forests
    (2007) Mucina L; Pienaar E; Van Niekerk, Adriaan; Lötter MC