4 research outputs found
Analysis of the performance of hydrogen maser clocks at the Hartebeesthoek Radio Astronomy Observatory
Hydrogen maser frequency standards are commonly utilised in various space geodetic techniques such as Very Long Baseline Interferometry (VLBI) as local reference clocks. The Hartebeesthoek Radio Astronomy Observatory in South Africa is currently operating two maser frequency standards i.e., an EFOS28 and an iMaser72 for the 15 m and 26 m VLBI radio telescopes respectively, an older EFOS6 is a standby spare. This study utilised the least-squares method to derive clock parameters, which indicates the performance levels of the masers by making use of the offset measurements obtained between hydrogen maser clock 1 PPS and GNSS 1 PPS for a period of 35 days. The masers were also compared using a frequency comparator (VCH-314) for a time period of 100 s. The results indicate that the performances of both Masers are relatively similar to each other, with short-term and long-term results indicating good agreement. The iMaser72 has a better standard error of 0.0039 μs compared to the standard error of 0.0059 μs for the EFOS28 maser clock. In general, both masers performed at an expected level required for radio astronomy and geodetic VLBI applications. The method used in this study proved to be useful in managing local hydrogen maser clocks to ensure accurate VLBI observations are obtained
Environmental factors and population at risk of malaria in Nkomazi municipality, South Africa
OBJECTIVE : Nkomazi local municipality of South Africa is a high-risk malaria region with an
incidence rate of about 500 cases per 100 000. We examined the influence of environmental factors
on population (age group) at risk of malaria.
methods R software was used to statistically analyse data. Using remote sensing technology, a Landsat
8 image of 4th October 2015 was classified using object-based classification and a 5-m resolution. Spot
height data were used to generate a digital elevation model of the area. RESULTS : A total of 60 718 malaria cases were notified across 48 health facilities in Nkomazi municipality between January 1997 and August 2015. Malaria incidence was highly associated with
irrigated land (P = 0.001), water body (P = 0.011) and altitude ≤400 m (P = 0.001). The multivariate
model showed that with 10% increase in the extent of irrigated areas, malaria risk increased by almost
39% in the entire study area and by almost 44% in the 2-km buffer zone of selected villages. Malaria
incidence is more pronounced in the economically active population aged 15–64 and in males. Both
incidence and case fatality rate drastically declined over the study period. CONCLUSION : A predictive model based on environmental factors would be useful in the effort towards malaria elimination by fostering appropriate targeting of control measures and allocating of resources.This study was supported by the EU project ‘Quantifying
Weather and Climate Impacts on health in developing
countries’, an European Commission’s Seventh Framework
Research Programme by providing a 2-year student
bursary to the primary author. We acknowledge the support
of the University of Pretoria, Centre for Sustainable
Malaria Control and of the Earth and Atmospheric
Remote Sensing Research Group, University of Pretoria.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-31562017-05-31hb2016Centre for Environmental StudiesCentre for Geoinformation ScienceGeography, Geoinformatics and Meteorolog
Comparison of Site Velocities Derived from Collocated GPS, VLBI and SLR Techniques at The Hartebeesthoek Radio Astronomy Observatory (Comparison of Site Velocities)
Space geodetic techniques provide highly accurate methods for estimating bedrock stability at subcentimetre level. We utilize data derived from Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI) and Global Positioning Systems (GPS) techniques, collocated at the Hartebeesthoek Radio Astronomy Observatory, to characterise local plate motion and compare the solutions from the three techniques. Data from the GNSS station were processed using the GAMIT/GLOBK (version 10.4) software, data from the SLR station (MOBLAS-6)were processed using the Satellite Laser Ranging Data Analysis Software (SDAS) and the VLBI data sets were processed using the Vienna VLBI Software (VieVS) software. Results show that there is a good agreement between horizontal and vertical velocity components with a maximum deviation of 1.7 mm/yr, 0.7 mm/yr and 1.3 mm/yr between the North, East and Up velocity components respectively for the different techniques. At HartRAO there is no significant trend in the vertical component and all the techniques used are consistent with the a-priori velocities when compared with each other. This information is crucial in monitoring the local motion variations since geodetic instruments require a very stable base to minimise measurement errors. These findings demonstrate that station coordinate time-series derived with different techniques and analysis strategies provide comparable results