Validation of the moderate-resolution satellite burned area products across different biomes in South Africa

Biomass burning in southern Africa has brought significant challenges to the research society as a fundamental driver of climate and land cover changes. Burned area mapping approaches have been developed that generate large-scale low and moderate resolution products made with different satellite data. This consequently afford the remote sensing community a unique opportunity to support their potential applications in e.g., examining the impact of fire on natural resources, estimating the quantities of burned biomass and gas emissions. Generally, the satellite-derived burned area products produced with dissimilar algorithms provide mapped burned areas at different levels of accuracy, as the environmental and remote sensing factors vary both spatially and temporally. This study focused on the inter-comparison and accuracy evaluation of the 500-meter Moderate Resolution Imaging Spetroradiomter (MODIS) burned area product (MCD45A1) and the Backup MODIS burned area product (hereafter BMBAP) across the main-fire prone South African biomes using reference data independently-derived from multi-temporal 30-meter Landsat 5 Thematic Mapper (TM) imagery distributed over six validation sites. The accuracy of the products was quantified using confusion matrices, linear regression and subpixel burned area measures. The results revealed that the highest burned area mapping accuracies were reported in the fynbos and grassland biomes by the MCD45A1 product, following the BMBAP product across the pine forest and savanna biomes, respectively. Further, the MCD45A1 product presented higher subpixel detection probabilities for the burned area fractions 50% of a MODIS pixel. Finally the results demonstrated that the probability of identifying a burned area within a MODIS pixel is directly related to the proportion of the MODIS pixel burned and thus, highlights the relevance of fractional burned area during classification accuracy assessment of lower resolution remotely-sensed products using data with higher spatial resolution.Dissertation (MSc)--University of Pretoria, 2011.Geography, Geoinformatics and Meteorologyunrestricte

Thermal analysis of the LLR optical telescope tube assembly based in Hartebeesthoek Radio Astronomy Observatory

The Hartebeesthoek Radio Astronomy Observatory of South Africa is currently developing a lunar laser ranger (LLR) system based on a one metre aperture telescope in collaboration with National Aeronautics and Space Administration and the Observatoire de la Côte d’Azur. This LLR will be an addition to a limited list of operating LLR stations globally and it is expected to achieve sub-centimetre range precision to the Moon. Key to this expectation including the overall telescope operational performance is thermal analysis of the telescope structure, based on the thermal properties of component materials and their interaction with the environment through conventional heat transfer mechanisms. This paper presents transient thermal simulation results of the telescope’s optical tube and one metre primary mirror in terms of thermal variations and consequent structural deformations. The results indicate that on a non-windy, cloud-free and winter day, the temperature gradients on the structure could be within 1 °C with respect to the temporal ambient air temperatures at the site when these are between 9 and 23 °C. Furthermore, these gradients were coupled with thermally-induced total deformations that vary between 2.9 and 40.7 μm of the assembled telescope components. In overall, these findings suggest that both the tube and especially the mirror may respond very slowly to ambient temperatures; however, correcting for structural thermal variations is imperative in maximizing the pointing accuracy of the telescope thereby increasing the chance being on-target with the retroreflectors located on the Moon surface.P. L. Tsela hereby acknowledges research support in part by the National Research Foundation of South Africa for the grant, Unique Grant No. 93952.http://link.springer.com/journal/403282017-09-30hb2016Geography, Geoinformatics and Meteorolog

Effect of impervious surface area and vegetation changes on mean surface temperature over Tshwane metropolis, Gauteng Province, South Africa

The Tshwane Metropolis, Gauteng Province, South Africa, continues to experience rapid urbanization as a result of population growth. This has led to the conversion of natural lands into large man-made landscapes i.e., increase in impervious surfaces and a decrease in vegetative cover. This land use or land cover changes are also thought to affect the climate of the Tshwane metropolis as is evidenced by heat waves in 2013 and 2014. This paper describes how vegetation and impervious surface area (ISA) or built up areas were classified from Landsat 8 LCDM, 2013, and Landsat 7 ETM+, 2003 images using thematic spectral indices and mean surface temperatures derived from the thermal bands. The linear relationship between the two land cover types and surface temperature (LST) derived from the thermal bands was also examined. The results of this research reveal that the ISA increase has occurred due to urban sprawl and this has contributed to increase in surface temperature.The Applied Centre for Climate and Earth System Science (ACCESS) and University of Pretoria.http://www.sajg.org.za/index.php/sajgam2016Geography, Geoinformatics and Meteorolog

Effect of impervious surface area and vegetation changes on mean surface temperature over Tshwane metropolis, Gauteng Province, South Africa

The Tshwane Metropolis, Gauteng Province, South Africa, continues to experience rapid urbanization as a result of population growth. This has led to the conversion of natural lands into large man-made landscapes i.e., increase in impervious surfaces and a decrease in vegetative cover. This land use or land cover changes are also thought to affect the climate of the Tshwane metropolis as is evidenced by heat waves in 2013 and 2014. This paper describes how vegetation and impervious surface area (ISA) or built up areas were classified from Landsat 8 LCDM, 2013, and Landsat 7 ETM+, 2003 images using thematic spectral indices and mean surface temperatures derived from the thermal bands. The linear relationship between the two land cover types and surface temperature (LST) derived from the thermal bands was also examined. The results of this research reveal that the ISA increase has occurred due to urban sprawl and this has contributed to increase in surface temperature.The Applied Centre for Climate and Earth System Science (ACCESS) and University of Pretoria.http://www.sajg.org.za/index.php/sajgam2016Geography, Geoinformatics and Meteorolog

Landsat satellite derived environmental metric for mapping mosquitoes breeding habitats in the Nkomazi municipality, Mpumalanga Province, South Africa

The advancement, availability and high level of accuracy of satellite data provide a unique opportunity to conduct environmental and epidemiological studies using remotely sensed measurements. In this study, information derived from remote sensing data is used to determine breeding habitats for Anopheles arabiensis which is the prevalent mosquito species over Nkomazi municipality. In particular, we have utilized the normalized difference vegetation index (NDVI) and normalized difference water index (NDWI) coupled with land surface temperature (LST) derived from Landsat 5 TM satellite data. NDVI, NDWI and LST are considered as key environmental factors that influence the mosquito habitation. The breeding habitat was derived using multi-criteria evaluation (MCE) within ArcGIS using the derived environmental metric with appropriate weight assigned to them. Additionally, notified malaria cases were analysed and spatial data layers of water bodies, including rivers and dams, were buffered to further illustrate areas at risk of malaria. The output map from the MCE was then classified into three classes which are low, medium and high areas. The resulting malaria risk map depicts that areas of Komatieport, Malelane, Madadeni and Tonga of the district are subjected to high malaria incidence. The time series analysis of environmental metrics and malaria cases can help to provide an adequate mechanism for monitoring, control and early warning for malaria incidence.The EU project QWeCI (Quantifying Weather and Climate Impacts on health in developing countries) and the European Commission’s Seventh Framework Research Programme under the [grant number 243964]).http://www.tandfonline.com/loi/rsag202017-12-30hb2016Geography, Geoinformatics and Meteorolog

Detecting changes in surface water area of Lake Kyoga sub-basin using remotely sensed imagery in a changing climate

Detection of changes in Earth surface features, for example lakes, is important for understanding the relationships between human and natural phenomena in order to manage better the increasingly scarce natural resources. This work presents a procedure of using Modified Normalised Difference Water Index (MNDWI) to detect fluctuations of Lake surface-water area and relate it to a changing climate. The study used radiometrically and geometrically rectified Landsat images for 1986, 1995 and 2010 encompassing the Kyoga Basin lakes of Uganda, in order to investigate the changes in surface-water area between the respective years. The Standard Precipitation Index (SPI) and Drought Severity Index (DSI) are applied to show the relationship between variability of surface-water area and climate parameters. The present analysis reveals that surface-water area fluctuation is linked to rainfall variability. In particular, Lake Kyoga sub-basin lakes experienced an increase in surface-water area in 2010 compared to 1986. This work has important implications to water resources management for Lake Kyoga and could be vital to water resource managers across Ugandan lakes.http://link.springer.com/journal/7042016-09-30hb2016Geography, Geoinformatics and Meteorolog

A spatiotemporal analysis of the effect of ambient temperatures on the thermal behaviour of the Lunar Laser Ranging optical telescope at Hartebeesthoek Radio Astronomy Observatory

Development of the 1-meter aperture Lunar Laser Ranging (LLR) telescope is underway at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) which is expected to achieve sub-centimeter range precision and accuracy to the Moon, for enhanced tests of Earth-Moon system dynamics. Key to the operational performance of the telescope is thermal analysis of the telescope composite structure including the optical mirrors. This study presents a thermal analysis on the integrated component materials comprising the LLR telescope in ANSYS, with the aim of simulating its thermal behaviour in response to site-based ambient air temperature (TA). Results show that for a full day TA profile spanning the time period 00:00 to 23:59 the resulting range of simulated thermal variations measured at 12:00 midday and 23:59 nighttime across the telescope composite structure was found to be 9.11 ºC to 10.03 ºC and 9.12 ºC to 9.86 ºC respectively. In particular, the spider assembly and outer tube surface had the largest range of thermal variations i.e. greater than absolute 1 ºC and thus, could be the main areas on the telescope where most thermal variations would occur. Furthermore, validation of the outer tube thermal variations using the 64 Resistant Temperature Detector (RTD) sensors mounted onto the test tube, showed relatable overall thermal variations of about 2 ºC, at wind speeds of 0 to 0.4 km/h. In overall, these findings provide a typical expectation of the LLR telescope thermal behavior in response to TA at the site; and thus could be used as a guide to develop an RTD-based thermal monitoring system for the HartRAO LLR optical telescope.The National Research Foundation of South Africahttp://www.sajg.org.za/index.php/sajgam2017Geography, Geoinformatics and Meteorolog

A spatiotemporal analysis of the effect of ambient temperatures on the thermal behaviour of the Lunar Laser Ranging optical telescope at Hartebeesthoek Radio Astronomy Observatory

Development of the 1-meter aperture Lunar Laser Ranging (LLR) telescope is underway at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) which is expected to achieve sub-centimeter range precision and accuracy to the Moon, for enhanced tests of Earth-Moon system dynamics. Key to the operational performance of the telescope is thermal analysis of the telescope composite structure including the optical mirrors. This study presents a thermal analysis on the integrated component materials comprising the LLR telescope in ANSYS, with the aim of simulating its thermal behaviour in response to site-based ambient air temperature (TA). Results show that for a full day TA profile spanning the time period 00:00 to 23:59 the resulting range of simulated thermal variations measured at 12:00 midday and 23:59 nighttime across the telescope composite structure was found to be 9.11 ºC to 10.03 ºC and 9.12 ºC to 9.86 ºC respectively. In particular, the spider assembly and outer tube surface had the largest range of thermal variations i.e. greater than absolute 1 ºC and thus, could be the main areas on the telescope where most thermal variations would occur. Furthermore, validation of the outer tube thermal variations using the 64 Resistant Temperature Detector (RTD) sensors mounted onto the test tube, showed relatable overall thermal variations of about 2 ºC, at wind speeds of 0 to 0.4 km/h. In overall, these findings provide a typical expectation of the LLR telescope thermal behavior in response to TA at the site; and thus could be used as a guide to develop an RTD-based thermal monitoring system for the HartRAO LLR optical telescope.The National Research Foundation of South Africahttp://www.sajg.org.za/index.php/sajgam2017Geography, Geoinformatics and Meteorolog