South African Journal of Geomatics https://www.ajol.info/index.php/sajg <p>The South African Journal of Geomatics (SAJG) publishes peer-reviewed original papers within the broad discipline of Geomatics (including surveying techniques, technology and applications, mine surveying, hydrographic surveying, cadastral systems, land tenure, development planning, GIS, photogrammetry and remote sensing). The journal is designed to serve as a source reference and archive of advancements in these disciplines. The focus is on papers relevant to the South African and African context, but is not restricted to these areas. This includes both technological developments as well as social adaptations appropriate to the needs of Geomatics in Africa.</p> <p>Other websites associated with this journal:&nbsp;<a title="http://www.sajg.org.za" href="http://www.sajg.org.za" target="_blank" rel="noopener">www.sajg.org.za</a></p> CONSAS en-US South African Journal of Geomatics 2225-8531 <p>Authors who submit papers to this journal agree to the following terms:</p><p>a) Authors retain copyright over their work, while allowing the journal to place this work on the journal website under a Creative Commons Attribution License, which allows others to freely access, use, and share the work, with an acknowledgment of the work's authorship and its initial publication in this journal.</p><p>b) Authors are able to waive the terms of the CC license and enter into separate, additional contractual arrangements for the non-exclusive distribution and subsequent publication of this work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgment of its initial publication in this journal.</p><p>c) In addition, authors are encouraged to post and share their work online (e.g., in institutional repositories or on their website) at any point after publication on the journal website.</p> Monitoring vegetation phenology using MODIS NDVI 250m in the City of Tshwane, South Africa https://www.ajol.info/index.php/sajg/article/view/231066 <p>The unprecedented influx of people into urban areas has led to the horizontal and vertical growth of urban environments. One of the notable impacts of urbanisation is the encroachment of urban-like environments into non-urban areas. This is common in both developed and developing countries, and South Africa’s City of Tshwane, the administrative capital of the country, has been affected by urbanisation because of migration. One of the parameters or proxies used to quantify urban growth is vegetation cover. There is a consensus that with the increase in the population of urban dwellers, vegetation cover will decrease. To assess and monitor vegetation cover, the Normalised Difference Vegetation Index (NDVI) is commonly used. In this study, MODIS NDVI data with a 250m spatial resolution was used to assess the impact of urban growth on vegetation. A time series analysis of the MODIS NDVI with a spatial resolution of 250m was used to establish the patterns of vegetation cover. Trends in vegetation change were determined in newly developed residential areas, informal settlements, and various vegetated areas. Sen's slope estimator and Mann-Kendall’s statisticwere used to analyse the spatial trends and variations in trends among different land cover classes. The slope of the trends differs significantly but there is a general decline in vegetation cover. The temporal profiles revealed the high and low NDVI values, respectively showing greening (high vegetation) and browning (low vegetation) trends from 2000 to 2016. It is concluded that urban growth has an impact on vegetation cover. However, this does not disturb the seasonal changes in vegetation where high NDVI values prevail in summer and low values in winter.</p> James Magidi Fethi Ahmed Copyright (c) 2022-09-01 2022-09-01 11 2 176 189 10.4314/sajg.v11i2.1 GIS investigation of the fire history of Jonkershoek Nature Reserve https://www.ajol.info/index.php/sajg/article/view/231067 <p>Fire regimes have the potential to disturb ecological aspects of a landscape and/or contribute to the maintenance of the biological diversity. Thus, a gauge of the impact of planned and unplanned fire regimes is vital to South Africa’s national reserves. The Jonkershoek Nature Reserve in the Western Cape is characterized by the occurrence of indigenous Fynbos and Afromontane Forest vegetation. Geographical Information Systems (GIS) and Remote Sensing (RS) can aid the management and preservation of indigenous vegetational species. This study used knowledge of the ecological conditions of the Reserve, historical fire data, Landsat TM and Landsat OLI imagery, and geospatial analysis to investigate the impact of the fire regimes in the Reserve. Image classification was carried out from 2005 to 2015 to determine the burn patterns, with the process being aided by the fire regime history from 1970 to 2015. Ordinary Least Squares (OLS) analysis was carried out to determine how abiotic factors, such as elevation, slope and aspect, impact fires in the Reserve. The assessment of fires included the ascertainment of their location, coverage, and frequency, the Normalised Burn Ratio (NBR), the differenced Normalised Burn Ratio (dNBR) and the Normalised Difference Vegetation Index (NDVI). There were 39 fires recorded in the Jonkershoek Nature Reserve from 1970 to 2015. The largest fire events were recorded in 1999 (26503.6 ha.) and 2015 (8363.0 ha.). The lowest area of fire impact recorded occurred in the years 2010 (0.15ha.), 1973 (1.1 ha.) and 1987 (3.1 ha.). With an overall classification accuracy of 94.17%, the Landsat OLI imagery performed better with an overall classification accuracy of 94.17% than the Landsat TM at 75.83%. The OLS regression showed that fire severity was positively correlated to NDVI and elevation. This may suggest that regions of healthy vegetation at any altitude may be susceptible to burnings if there is sufficient vegetation to fuel a fire. The OLS was negatively correlated to slope and aspect. This may impact fire risk as steeper slopes may have vegetation growing in their fire shadow.</p> S. Mashele K Singh Copyright (c) 2022-09-01 2022-09-01 11 2 189 201 10.4314/sajg.v11i2.2 Geospatial assessment of land use/cover, rainfall, and flood incidents in Eti–Osa, Lagos, Nigeria https://www.ajol.info/index.php/sajg/article/view/231068 <p>Flooding in Lagos State has been on the rise in the past two decades, especially in the Eti-Osa area of the state. This is largely due to the increased volume of rainfall associated with climate variability and sea level rise. Flooding incidents have led to loss of lives and properties. The objective of this study is to examine the dynamics of flood occurrences in the Eti-Osa area of Lagos metropolis. Rainfall data for the area covering a period of 30 years (1990 to 2019) were obtained from the Nigerian Meteorological Agency (NiMET) in Lagos, and analyzed using the basic descriptive statistical technique. The purpose was to evaluate rainfall characteristics that were influencing flooding events in the area. Furthermore, remotely sensed multi-date Landsat imageries of 1990, 1997, 2001, 2012, and 2017 were obtained, and analyzed to determine how land use and land cover characteristics have changed and have been affected by flooding over the study period. The data were subjected to digital image processing and supervised classification was carried out on the images of the various dates. Results showed that flooding became prevalent as more areas became built up and as vegetated areas declined. Also, flooding events appeared to be responsive to the climatic extremes. Moreover, poor drainage, increased population number s, and non-compliance to building and current environmental regulations were key factors that exacerbated the increased prevalence of flooding in the area. The study recommended that flood control policies, including land-use planning for the area, need to be pursued urgently.<br><br></p> Toka Sunday Onajomo Copyright (c) 2022-09-01 2022-09-01 11 2 202 217 10.4314/sajg.v11i2.3 Applying Malawi Continuously Operating Reference Stations (CORS) in GNSS Meteorology https://www.ajol.info/index.php/sajg/article/view/231069 <p>Global Navigation Satellite System (GNSS) signals in the L-band are affected by the non-dispersive neutral atmosphere. Regardless of their center frequency, the L-band code and phase observations are affected by the same measure of delay. GNSS receivers play a significant role in quantifying the zenith tropospheric delay (ZTD) from satellite signals. Malawi has a Continuously Operating Reference Stations (CORS) network which was established to support research in geophysical geodesy and geodynamics. However, the quality of the observations tracked by the CORS has never been tested in terms of its meteorological application. In this paper, the ZTD estimation approach and the evaluation of results from the Global Positioning System (GPS) measurements are presented. The optimal approach of precise point positioning (PPP) was used to estimate ZTD from one-week datasets which were collected from six CORS monuments distributed in the northern and southern regions of Malawi. In addition, the zenith wet delay (ZWD) and zenith hydrostatic delay (ZHD) were also estimated to determine their respective contributions to the total delay in all the stations. Alongside the meteorological parameters, the positioning repeatabilities were also established for all stations. Results indicate that the averaged ZTD, ZWD and ZHD can reach as high as 247mm, 47 mm, and 199 mm, respectively. The minimum ZTD, ZWD, and ZHD for the stations can drop to as low as 220 mm, 24 mm, and 181 mm, respectively. This indicates that the ZHD contributes to more than 90% of the total delay at the stations. For the positioning performance, there was no obvious disparity in the latitude (less than 0.5 cm), longitude (less than 1 cm), and ellipsoidal height repeatabilities (less than 1.5 cm). Thus, the results clearly demonstrate that the Malawi CORS network may be used for GNSS-based meteorological applications using the available geodetic receivers. However, for high precision meteorological applications, Malawi may consider densifying the available network with geodetic grade receivers.</p> <p>&nbsp;</p> Robert Galatiya Suya Charles Chisha Kapachika Mphatso Oscar Soko Vincent Luhanga John Bosco Ogwang Harvey Chilembwe Francis Gitau Copyright (c) 2022-09-01 2022-09-01 11 2 218 233 10.4314/sajg.v11i2.4 The application of Geographical Information Systems to armed violent conflict resolution and peacebuilding: a literature review https://www.ajol.info/index.php/sajg/article/view/231070 <p>Many conventional approaches to resolving armed violent conflicts, including negotiations, peace talks, and stabilization, have been adopted, especially in Asia and Africa, but sustainable peace is still illusive in some of these areas. Most of these approaches emphasize the economic and political aspects of peace negotiations and tend to ignore the spatial component. There are several innovative technologies, such as smart cell phones, the internet, Global Position Systems (GPS), and satellite data for mapping armed violent conflict resolution. However, GIS has been recognized as an invaluable tool, a decision support system, and has the potential to assist in conflict resolution. This paper aims to review literature on the application of GIS in the prevention of armed violent conflict, its resolution, post-conflict reconstruction, and peacebuilding. The literature review reveals that while GIS continues to be applied in armed violent conflict resolution and peacebuilding, several challenges remain, including amongst others, its availability, its acceptance by conflicting parties, its accessibility, the accuracy of its data, and the expertise of GIS personnel undertaking the data analysis and integration of data from different sources. A suggested area of further study includes either the application of remote sensing to violent conflict resolution or an integrated application of GIS and Remote Sensing to armed conflict resolution.</p> Stanislas Rwandarugali Njoya Ngeta Copyright (c) 2022-09-01 2022-09-01 11 2 234 246 10.4314/sajg.v11i2.5 The effect of poorly controlled physical development on urban food production in Ibadan, Nigeria https://www.ajol.info/index.php/sajg/article/view/231071 <p>Urban expansion, mainly occasioned by poorly controlled physical development, continues to pose severe threats to sustainable food production. While studies have concentrated more on food production in the hinterlands of Nigeria, there is a dearth of information on empirical investigations into urban food supply. This study, therefore, examined the effect of poorly controlled physical development on urban food production in Ibadan. An ecological footprint model was used to provide its theoretical anchor, while a longitudinal survey was the research design of choice. Both primary and secondary data were sourced. Geographical and remote sensing methods of analysis were used, with the primary focus being on Ibadan City and the dairy farm that has been converted to non-agricultural uses. This research revealed that Ibadan’s total urban area increased from 70.3584 ha in 1986 to 411.8877 ha in 2019. This expansion was accompanied by the loss of agricultural land, the depletion of water bodies, and agricultural land conversion. Validation of the research findings revealed a relatively high accuracy in terms of the Kappa value of 0.72 and an overall classification accuracy of 79.17% for 1986, of 0.84 and 88.33% for 2000, and of 0.91 and 92.5% for 2019. This studyrecommends that farmers should be trained on soilless farming practices such as aeroponics and hydroponics which both require relatively small portions of land to produce food.</p> Umar Usman Jimoh Kolade Victor Otokiti Copyright (c) 2022-09-01 2022-09-01 11 2 247 261 10.4314/sajg.v11i2.6 Remote sensing-based evapotranspiration determination: A review of single-source energy balance models https://www.ajol.info/index.php/sajg/article/view/231072 <p>Remote Sensing evapotranspiration models are critical in order to understand the cycling of water in the environment. Initially, an outline of the concepts related to evapotranspiration, as well as the shortcomings of land-based methods, is presented. The aim of the study was based on reviewing remote sensing evapotranspiration models which provide an alternative data source. These models have proved to be a cheaper alternative to mapping and estimating spatiotemporal evapotranspiration measurements across local and regional scales. This paper reviews the single-source energy balance model, which differs from the two-source model, for estimating spatiotemporal measurements of evapotranspiration. The single-source energy balance model is underpinned by mathematical equations which differentiate the various single-source evapotranspiration models (Surface Energy Balance Systems, Simplified Surface Energy Systems, Surface Energy Balance Algorithm, and Mapping Evapotranspiration at high Resolution and with Internalised Calibration). The soil surface and forest canopy components were observed to be the major difference between the single and dual-source models. Further advice was discussed on the implementation of the OpenET tool, which provides an open and accessible satellite-based estimation of evapotranspiration for improved water management.</p> Lehlohonolo Sello Akhona Maqhubela Gaathier Mahed Copyright (c) 2022-09-01 2022-09-01 11 2 262 273 10.4314/sajg.v11i2.7 Congruence through repeatability of position solutions by different GNSS survey techniques https://www.ajol.info/index.php/sajg/article/view/231073 <p>In this study, we determined three-dimensional (3D) position coordinates for eight new Continuous Operating Reference Stations (CORS) in Ghana through three different GNSS positioning techniques. The three GNSS positioning techniques whereby the network of CORS was tied to ITRF14 and War Office 1926 datums included:1) Precise Point Positioning (PPP); 2) Precise Differential GNSS (PDGNSS), using reference stations based on ITRF14; and 3) PDGNSS, using reference stations based on War Office. The PPP solutions were computed using the Canadian Spatial Reference System Precise Point Positioning software (CSRS-PPP), available online and as an open source GNSS laboratory tool software (gLAB). The PDGNSS solutions were obtained from OPUS and AUSPOS online services, as well as from self-post-processing using Topcon Tools software v8.2.3. All solutions were computed using 24-hour data for twelve consecutive days in the month of October 2018 (GPS DoY 284 to GPS DoY 295). The quality, reliability, and acceptability of position solutions were measured by computing the average positioning error, the rate of ambiguity resolution and the repeatability ratios of the solutions. The variability of coordinate differences for each pair of different positioning techniques was computed to determine their solution congruences. Ultimately, , the average positioning errors in northing, easting, and height were 0.003m, 0.005m and 0.009m, respectively. The rate of ambiguity resolution was between 75.3% and 90.3%. Repeatability ratios ranged between 1: 68,500,000 and 1: 411,100,000. Finally, the minimum and maximum range of variability in coordinate differences for each pair of positioning techniques was 1mm to 16mm for horizontal positions and 2mm to 137mm for vertical positions.</p> Osman Mohammed Abukari Akwasi Afrifa Acheampong Isaac Dadzie Samuel Osah Copyright (c) 2022-09-01 2022-09-01 11 2 274 289 10.4314/sajg.v11i2.8 Small dams: determining the minimum waterbody surface area that can be successfully detected using Sentinel-1 SAR imagery https://www.ajol.info/index.php/sajg/article/view/231083 <p>Water is a scarce resource in South Africa, and approximately 62% of the water used in South Africa is for irrigation. This water is stored in many small dams scattered across the country. If not managed correctly, they could have a negative effect on catchment areas and on the availability of water. As such, there is a need for a new monitoring and management system to be developed. This study determined the minimum surface area that would be required for a waterbody to be detected on Sentinel-1 Synthetic Aperture Radar imagery. A Random Forest classifier was used to detect waterbodies on a Sentinel-1 image calculated from a time series of imagery taken over a period of three months. Steep incidence angles outperformed shallow incidence angles, with the classification having an overall accuracy of 80%. Detection rates were almost 90% for waterbodies of one hectare and greater, with no false positives, and a 10% false negative rate. These findings provide the foundation for developing a detection and monitoring system, which would allow for the better management of water resources in South Africa.</p> M von Fintel J. Kemp Copyright (c) 2022-09-02 2022-09-02 11 2 290 309 10.4314/sajg.v11i2.9 Geospatial assessment of land suitability for oil palm (<i>Elaeis guineensis</i> Jacq.) growing in Northern Uganda. https://www.ajol.info/index.php/sajg/article/view/231084 <p>Under the second phase of the National Oil Palm Project, the Government of Uganda plans to extend the oil palm project to Northern Uganda. According to the Final Project Design Report (2017) of the National Oil Palm Project, and based on the rainfall, soil and temperature of the region, areas in Northern Uganda have already been mapped for the project. However, no detailed information on the degree of suitability of the areas has been provided. In this research, other parameters such as land cover, elevation and slope were identified through the literature review. Furthermore, on the basis of the reclassify tool in ArcMap 10.8, the data were then reclassified into four classes, namely, highly suitable (S1), moderately suitable (S2), marginally suitable (S3) and unsuitable (N.) With the aid of the Analytical Hierarchical Process (AHP), pairwise comparison matrices were constructed and the weight of each parameter was computed. The suitability map obtained from a weighted linear combination identified 38.18%, 35.54%, 21.41% and 4.87% of the land area as highly suitable, moderately suitable, marginally suitable and unsuitable, respectively. A geospatial assessment of the suitability of the land for oil palm growing was carried out. It was based on only the soil types, but excluded the chemical properties of the soil. Therefore, further research on the chemical properties of the soils at suitable sites should be carried out. In-depth research should be carried out While considering social and economic factors among the criteria to determine the willingness and financial capability of the people to venture into oil palm growing as a source of income, Oil Palm Uganda Limited should conduct in-depth research into this issue.</p> Anjo Abraham Ivan Bamweyana Copyright (c) 2022-09-02 2022-09-02 11 2 310 324 10.4314/sajg.v11i2.10 Analysing the changes in the bathymetry of Saldanha Bay between the years 1977 and 2021 https://www.ajol.info/index.php/sajg/article/view/231089 <p>The construction of the Saldanha Port has been the reason for the major changes in the bathymetry and sediment dynamics observed in Saldanha Bay in the last decades. In this paper, newly acquired soundings from the National Hydrographer were used to analyse the changes between 1977 and 2021 - over a 44-year period - in the bathymetry of Saldanha Bay. The Ordinary Kriging (OK) interpolation method, available through the Geostatistical Wizard in ArcGIS Pro, was used for creating surface models to conduct comparisons with the bathymetry of Saldanha Bay. The results indicate a general increase in depth since 1977 of between 0.395 and 3.203 m, and an average increase in depth within the Big Bay of 1.799 m. Between 1977 and 2021, a total volume loss of 49 364 560.0 m3 in sediment was calculated - an indication of how the sedimentation process in Saldanha Bay has changed subsequent to the construction of the harbour.</p> Louis Du Toit Ivan Henrico Jacques Bezuidenhout Babalwa Mtshawu Copyright (c) 2022-09-02 2022-09-02 11 2 325 339 10.4314/sajg.v11i2.11