Urban heat island (UHI) is an important phenomenon given its direct and indirect impacts on human populations in urban environments. The UHI phenomenon has been studied extensively using both directly measured and remotely sensed temperature data sets. This review presents an overview of the UHI background concepts and provides details of satellite remote sensing data and processing techniques applied by various studies to retrieve land surface temperatures (LSTs) in order to establish the existence of this phenomenon. The review reveals that various factors influence the utility of remote sensing in UHI studies. However, remote sensing has the potential to provide fairly accurate LST measurements that could be used to characterize UHI over large areas. UHI studies have been conducted mostly in the Americas, Europe and Asia with very few studies in Africa. Recommendations on means to improve the use of remote sensing in UHI studies have been made. Accurate and up-to-date remotely sensed assessments of UHIs will inform city planners and managers and assist in addressing challenges related to the phenomenon.

Estimation of Maize grain yield using multispectral satellite data sets (SPOT 5) and the random forest algorithm

The Rietspruit is located in Gauteng Province, South Africa, within the Witwatersrand Basin. The basin is noted for its vast gold deposit. The river extends for about 60 km before joining the Vaal River. The aim of this study was to determine the concentration of uranium in the Rietspruit and the factors that influenced the concentration of U at each of the sites. The source of uranium in the river is the discharge from the gold mine and the mine wastes. Inductively coupled plasma mass spectrometry was used for water and sediment analysis in order to determine the concentration of U. High concentration of U was found in the river water and sediment, which is above the permissible limit of U. The water is used for irrigation of farmlands, cattle watering and for human consumption despite the high concentration of uranium in it. Ingestion of uranium is dangerous to human health. Due to the toxic nature of uranium, consumption of the water for domestic use and agriculture purpose must be discouraged.

Population increase within urban environments especially in the developing countries, has posed a need to understand the urban climates. While the importance of urban climates cannot be overemphasized, acquiring knowledge about contributing factors to urban climates can be challenging. Measuring land surface temperatures is one of the ways to acquire such knowledge which could be an uphill task if done manually. However, satellite remote sensing data could be applied to spatially estimate such factors. Land surface temperatures (LST) were estimated from the thermal bands of the Landsat Enhanced Thermal Mapper Plus (ETM+) using remote sensing and geographic information system (GIS) techniques. In addition, meteorological data which included air temperature and relative humidity for the same satellite image dates were used in the analysis. Results showed that Durban metropolitan area is experiencing a major heat island over the city centre with some micro ones around the metro. Comparing the LST results to the landuse/cover of the city showed the UHI phenomenon is a reality with a 3°C and 4°C LST increase over the city centre of Durban for winter and summer seasons respectively in 2012 and being attributed greatly to the human activities within the area that has led to increase thermal radiation from land surface over highly dense and paved areas. Keywords: Urban growth, urban heat Island, land surface temperatures, satellite remote sensing

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Urban Heat Island (UHI) is among some of the challenges plaguing urban environments. There is increase human population within urban environments especially in the developing world, which is a need to understand the climates for their wellbeing. The use of multispectral satellite remote sensing to investigate the climatic conditions through radiation measurement is applied across the two major South African cities. The thermal remote sensing technique applied for this study is the direct determination of land surface temperatures (LST) using multispectral thermal imagery (ETM+). In addition, meteorological data which included air temperature and relative humidity for the same satellite image dates were used. The LST values obtained showed Johannesburg has many micro heat islands scattered across the metro than in Cape Town. These areas of heat islands corresponded to areas of human settlement and more so the unplanned as opposed to the planned ones. The estimated LST values and observed air temperature values with an R² of 0.9. It could be concluded that expansion of urban areas in South Africa has led to increased thermal radiation of land surface in densely populated areas.