Updating the ionospheric propagation factor, M(3000)F2, global model using the neural network technique and relevant geophysical input parameters
- Oronsaye, Samuel Iyen Jeffrey
- Authors: Oronsaye, Samuel Iyen Jeffrey
- Date: 2013
- Subjects: Neural networks (Computer science) , Ionospheric radio wave propagation , Ionosphere , Geophysics , Ionosondes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5434 , http://hdl.handle.net/10962/d1001609 , Neural networks (Computer science) , Ionospheric radio wave propagation , Ionosphere , Geophysics , Ionosondes
- Description: This thesis presents an update to the ionospheric propagation factor, M(3000)F2, global empirical model developed by Oyeyemi et al. (2007) (NNO). An additional aim of this research was to produce the updated model in a form that could be used within the International Reference Ionosphere (IRI) global model without adding to the complexity of the IRI. M(3000)F2 is the highest frequency at which a radio signal can be received over a distance of 3000 km after reflection in the ionosphere. The study employed the artificial neural network (ANN) technique using relevant geophysical input parameters which are known to influence the M(3000)F2 parameter. Ionosonde data from 135 ionospheric stations globally, including a number of equatorial stations, were available for this work. M(3000)F2 hourly values from 1976 to 2008, spanning all periods of low and high solar activity were used for model development and verification. A preliminary investigation was first carried out using a relatively small dataset to determine the appropriate input parameters for global M(3000)F2 parameter modelling. Inputs representing diurnal variation, seasonal variation, solar variation, modified dip latitude, longitude and latitude were found to be the optimum parameters for modelling the diurnal and seasonal variations of the M(3000)F2 parameter both on a temporal and spatial basis. The outcome of the preliminary study was applied to the overall dataset to develop a comprehensive ANN M(3000)F2 model which displays a remarkable improvement over the NNO model as well as the IRI version. The model shows 7.11% and 3.85% improvement over the NNO model as well as 13.04% and 10.05% over the IRI M(3000)F2 model, around high and low solar activity periods respectively. A comparison of the diurnal structure of the ANN and the IRI predicted values reveal that the ANN model is more effective in representing the diurnal structure of the M(3000)F2 values than the IRI M(3000)F2 model. The capability of the ANN model in reproducing the seasonal variation pattern of the M(3000)F2 values at 00h00UT, 06h00UT, 12h00UT, and l8h00UT more appropriately than the IRI version is illustrated in this work. A significant result obtained in this study is the ability of the ANN model in improving the post-sunset predicted values of the M(3000)F2 parameter which is known to be problematic to the IRI M(3000)F2 model in the low-latitude and the equatorial regions. The final M(3000)F2 model provides for an improved equatorial prediction and a simplified input space that allows for easy incorporation into the IRI model.
- Full Text:
- Date Issued: 2013
- Authors: Oronsaye, Samuel Iyen Jeffrey
- Date: 2013
- Subjects: Neural networks (Computer science) , Ionospheric radio wave propagation , Ionosphere , Geophysics , Ionosondes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5434 , http://hdl.handle.net/10962/d1001609 , Neural networks (Computer science) , Ionospheric radio wave propagation , Ionosphere , Geophysics , Ionosondes
- Description: This thesis presents an update to the ionospheric propagation factor, M(3000)F2, global empirical model developed by Oyeyemi et al. (2007) (NNO). An additional aim of this research was to produce the updated model in a form that could be used within the International Reference Ionosphere (IRI) global model without adding to the complexity of the IRI. M(3000)F2 is the highest frequency at which a radio signal can be received over a distance of 3000 km after reflection in the ionosphere. The study employed the artificial neural network (ANN) technique using relevant geophysical input parameters which are known to influence the M(3000)F2 parameter. Ionosonde data from 135 ionospheric stations globally, including a number of equatorial stations, were available for this work. M(3000)F2 hourly values from 1976 to 2008, spanning all periods of low and high solar activity were used for model development and verification. A preliminary investigation was first carried out using a relatively small dataset to determine the appropriate input parameters for global M(3000)F2 parameter modelling. Inputs representing diurnal variation, seasonal variation, solar variation, modified dip latitude, longitude and latitude were found to be the optimum parameters for modelling the diurnal and seasonal variations of the M(3000)F2 parameter both on a temporal and spatial basis. The outcome of the preliminary study was applied to the overall dataset to develop a comprehensive ANN M(3000)F2 model which displays a remarkable improvement over the NNO model as well as the IRI version. The model shows 7.11% and 3.85% improvement over the NNO model as well as 13.04% and 10.05% over the IRI M(3000)F2 model, around high and low solar activity periods respectively. A comparison of the diurnal structure of the ANN and the IRI predicted values reveal that the ANN model is more effective in representing the diurnal structure of the M(3000)F2 values than the IRI M(3000)F2 model. The capability of the ANN model in reproducing the seasonal variation pattern of the M(3000)F2 values at 00h00UT, 06h00UT, 12h00UT, and l8h00UT more appropriately than the IRI version is illustrated in this work. A significant result obtained in this study is the ability of the ANN model in improving the post-sunset predicted values of the M(3000)F2 parameter which is known to be problematic to the IRI M(3000)F2 model in the low-latitude and the equatorial regions. The final M(3000)F2 model provides for an improved equatorial prediction and a simplified input space that allows for easy incorporation into the IRI model.
- Full Text:
- Date Issued: 2013
Multi-instrument observations of ionospheric irregularities over South Africa
- Authors: Amabayo, Emirant Bertillas
- Date: 2012
- Subjects: Ionosphere -- Research , Sudden ionospheric disturbances , Ionospheric storms , Solar activity , Sunspots
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5476 , http://hdl.handle.net/10962/d1005261 , Ionosphere -- Research , Sudden ionospheric disturbances , Ionospheric storms , Solar activity , Sunspots
- Description: The occurrence of mid-latitude spread F (SF) over South Africa has not been extensively studied since the installation of the DPS-4 digisondes at Madimbo (30.88◦E, 22.38◦S), Grahamstown (33.32◦S, 26.50◦E) and Louisvale (28.51◦S, 21.24◦E). This study is intended to quantify the probability of the occurrence of F region disturbances associated with ionospheric spread F (SF) and L-band scintillation over South Africa. This study used available ionosonde data for 8 years (2000-2008) from the three South African stations. The SF events were identified manually on ionograms and grouped for further statistical analysis into frequency SF (FSF), range SF (RSF) and mixed SF (MSF). The results show that the diurnal pattern of SF occurrence peaks strongly between 23:00 and 00:00 UT. This pattern is true for all seasons and types of SF at Madimbo and Grahamstown during 2001 and 2005, except for RSF which had peaks during autumn and spring during 2001 at Madimbo. The probability of both MSF and FSF tends to increase with decreasing sunspot number (SSN), with a peak in 2005 (a moderate solar activity period). The seasonal peaks of MSF and FSF are more frequent during winter months at both Madimbo and Grahamstown. In this study SF was evident in ∼ 0.03% and ∼ 0.06% of the available ionograms at Madimbo and Grahamstown respectively during the eight year period. The presence of ionospheric irregularities associated with SF and scintillation was investigated using data from selected Global Positioning System (GPS) receiver stations distributed across South Africa. The results, based on GPS total electron content (TEC) and ionosonde measurements, show that SF over this region can most likely be attributed to travelling ionospheric disturbances (TIDs), caused by gravity waves (GWs) and neutral wind composition changes. The GWs were mostly associated with geomagnetic storms and sub-storms that occurred during periods of high and moderate solar activity (2001-2005). SF occurrence during the low solar activity period (2006-2008)can probably be attributed to neutral wind composition changes.
- Full Text:
- Date Issued: 2012
- Authors: Amabayo, Emirant Bertillas
- Date: 2012
- Subjects: Ionosphere -- Research , Sudden ionospheric disturbances , Ionospheric storms , Solar activity , Sunspots
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5476 , http://hdl.handle.net/10962/d1005261 , Ionosphere -- Research , Sudden ionospheric disturbances , Ionospheric storms , Solar activity , Sunspots
- Description: The occurrence of mid-latitude spread F (SF) over South Africa has not been extensively studied since the installation of the DPS-4 digisondes at Madimbo (30.88◦E, 22.38◦S), Grahamstown (33.32◦S, 26.50◦E) and Louisvale (28.51◦S, 21.24◦E). This study is intended to quantify the probability of the occurrence of F region disturbances associated with ionospheric spread F (SF) and L-band scintillation over South Africa. This study used available ionosonde data for 8 years (2000-2008) from the three South African stations. The SF events were identified manually on ionograms and grouped for further statistical analysis into frequency SF (FSF), range SF (RSF) and mixed SF (MSF). The results show that the diurnal pattern of SF occurrence peaks strongly between 23:00 and 00:00 UT. This pattern is true for all seasons and types of SF at Madimbo and Grahamstown during 2001 and 2005, except for RSF which had peaks during autumn and spring during 2001 at Madimbo. The probability of both MSF and FSF tends to increase with decreasing sunspot number (SSN), with a peak in 2005 (a moderate solar activity period). The seasonal peaks of MSF and FSF are more frequent during winter months at both Madimbo and Grahamstown. In this study SF was evident in ∼ 0.03% and ∼ 0.06% of the available ionograms at Madimbo and Grahamstown respectively during the eight year period. The presence of ionospheric irregularities associated with SF and scintillation was investigated using data from selected Global Positioning System (GPS) receiver stations distributed across South Africa. The results, based on GPS total electron content (TEC) and ionosonde measurements, show that SF over this region can most likely be attributed to travelling ionospheric disturbances (TIDs), caused by gravity waves (GWs) and neutral wind composition changes. The GWs were mostly associated with geomagnetic storms and sub-storms that occurred during periods of high and moderate solar activity (2001-2005). SF occurrence during the low solar activity period (2006-2008)can probably be attributed to neutral wind composition changes.
- Full Text:
- Date Issued: 2012
Using co-located radars and instruments to analyse ionespheric events over South Africa
- Authors: Athieno, Racheal
- Date: 2012
- Subjects: Ionosphere -- Research -- South Africa , Space environment -- Research -- South Africa , Meteorology -- Research -- South Africa , Ionosondes -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5493 , http://hdl.handle.net/10962/d1005279 , Ionosphere -- Research -- South Africa , Space environment -- Research -- South Africa , Meteorology -- Research -- South Africa , Ionosondes -- Research -- South Africa
- Description: Space weather and its effect on technological systems are important for scientific research. Developing an understanding of the behaviour, sources and effects of ionospheric events form a basis for improving space weather prediction. This thesis attempts to use co-located radars and instruments for the analysis of ionospheric events over South Africa. The HF Doppler radar, ionosonde, Global Positioning System (GPS) and GPS ionospheric scintillation monitor (GISTM) receivers are co-located in Hermanus (34.4°S, 19.2°E), one of the observatories for the space science directorate of the South African National Space Agency (SANSA). Data was obtained from these radars and instruments and analysed for ionospheric events. Only the Hermanus station was selected for this analysis, because it is currently the only South African station that hosts all the mentioned radars and instruments. Ionospheric events identified include wave-like structures, Doppler spread, sudden frequency deviations and ionospheric oscillations associated with geomagnetic pulsations. For the purpose of this work, ionospheric events are defined as any unusual structures observed on the received signal and inferred from observations made by the HF Doppler radar. They were identified by visual inspection of the Doppler shift spectrograms. The magnitude and nature of the events vary, depending on their source and were observed by all, some or one instrument. This study suggests that the inclusion of a wider data coverage and more stations in South Africa merit consideration, especially since plans are underway to host a co-located radar network similar to that in Hermanus at at least three additional observatory sites in South Africa. This study lays a foundation for multi-station co-located radar and instrument observation and analysis of ionospheric events which should enhance the accuracy of space weather and HF communication prediction.
- Full Text:
- Date Issued: 2012
- Authors: Athieno, Racheal
- Date: 2012
- Subjects: Ionosphere -- Research -- South Africa , Space environment -- Research -- South Africa , Meteorology -- Research -- South Africa , Ionosondes -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5493 , http://hdl.handle.net/10962/d1005279 , Ionosphere -- Research -- South Africa , Space environment -- Research -- South Africa , Meteorology -- Research -- South Africa , Ionosondes -- Research -- South Africa
- Description: Space weather and its effect on technological systems are important for scientific research. Developing an understanding of the behaviour, sources and effects of ionospheric events form a basis for improving space weather prediction. This thesis attempts to use co-located radars and instruments for the analysis of ionospheric events over South Africa. The HF Doppler radar, ionosonde, Global Positioning System (GPS) and GPS ionospheric scintillation monitor (GISTM) receivers are co-located in Hermanus (34.4°S, 19.2°E), one of the observatories for the space science directorate of the South African National Space Agency (SANSA). Data was obtained from these radars and instruments and analysed for ionospheric events. Only the Hermanus station was selected for this analysis, because it is currently the only South African station that hosts all the mentioned radars and instruments. Ionospheric events identified include wave-like structures, Doppler spread, sudden frequency deviations and ionospheric oscillations associated with geomagnetic pulsations. For the purpose of this work, ionospheric events are defined as any unusual structures observed on the received signal and inferred from observations made by the HF Doppler radar. They were identified by visual inspection of the Doppler shift spectrograms. The magnitude and nature of the events vary, depending on their source and were observed by all, some or one instrument. This study suggests that the inclusion of a wider data coverage and more stations in South Africa merit consideration, especially since plans are underway to host a co-located radar network similar to that in Hermanus at at least three additional observatory sites in South Africa. This study lays a foundation for multi-station co-located radar and instrument observation and analysis of ionospheric events which should enhance the accuracy of space weather and HF communication prediction.
- Full Text:
- Date Issued: 2012
Investigation into the extended capabilities of the new DPS-4D ionosonde
- Authors: Ssessanga, Nicholas
- Date: 2011
- Subjects: Ionosondes , Ionosphere , Ionosphere -- Observations -- South Africa -- Hermanus (Cape of Good Hope) , Ionosphere -- Research -- South Africa -- Hermanus (Cape of Good Hope)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5472 , http://hdl.handle.net/10962/d1005257 , Ionosondes , Ionosphere , Ionosphere -- Observations -- South Africa -- Hermanus (Cape of Good Hope) , Ionosphere -- Research -- South Africa -- Hermanus (Cape of Good Hope)
- Description: The DPS-4D is the latest version of digital ionosonde developed by the UMLCAR (University of Massachusetts in Lowell Center for Atmospheric Research) in 2008. This new ionosonde has advances in both the hardware and software which allows for the promised advanced capabilities. The aim of this thesis was to present results from an experiment undertaken using the Hermanus DPS-4D (34.4°S 19.2°E, South Africa), the first of this version to be installed globally, to answer a science question outside of the normally expected capabilities of an ionosonde. The science question posed focused on the ability of the DPS-4D to provide information on day-time Pc3 pulsations evident in the ionosphere. Day-time Pc3 ULF waves propagating down through the ionosphere cause oscillations in the Doppler shift of High Frequency (HF) radio transmissions that are correlated with the magnetic pulsations recorded on the ground. Evidence is presented which shows that no correlation exists between the ground magnetic pulsation data and DPS-4D ionospheric data. The conclusion was reached that although the DPS-4D is more advanced in its eld of technology than its predecessors it may not be used to observe Pc3 pulsations.
- Full Text:
- Date Issued: 2011
- Authors: Ssessanga, Nicholas
- Date: 2011
- Subjects: Ionosondes , Ionosphere , Ionosphere -- Observations -- South Africa -- Hermanus (Cape of Good Hope) , Ionosphere -- Research -- South Africa -- Hermanus (Cape of Good Hope)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5472 , http://hdl.handle.net/10962/d1005257 , Ionosondes , Ionosphere , Ionosphere -- Observations -- South Africa -- Hermanus (Cape of Good Hope) , Ionosphere -- Research -- South Africa -- Hermanus (Cape of Good Hope)
- Description: The DPS-4D is the latest version of digital ionosonde developed by the UMLCAR (University of Massachusetts in Lowell Center for Atmospheric Research) in 2008. This new ionosonde has advances in both the hardware and software which allows for the promised advanced capabilities. The aim of this thesis was to present results from an experiment undertaken using the Hermanus DPS-4D (34.4°S 19.2°E, South Africa), the first of this version to be installed globally, to answer a science question outside of the normally expected capabilities of an ionosonde. The science question posed focused on the ability of the DPS-4D to provide information on day-time Pc3 pulsations evident in the ionosphere. Day-time Pc3 ULF waves propagating down through the ionosphere cause oscillations in the Doppler shift of High Frequency (HF) radio transmissions that are correlated with the magnetic pulsations recorded on the ground. Evidence is presented which shows that no correlation exists between the ground magnetic pulsation data and DPS-4D ionospheric data. The conclusion was reached that although the DPS-4D is more advanced in its eld of technology than its predecessors it may not be used to observe Pc3 pulsations.
- Full Text:
- Date Issued: 2011
Comparison of A₄ neutrino mass models
- Barry, James Munnik Hamilton
- Authors: Barry, James Munnik Hamilton
- Date: 2010
- Subjects: Neutrinos -- Mass , Standard model (Nuclear physics) , Particles (Nuclear physics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5554 , http://hdl.handle.net/10962/d1015271
- Description: The present neutrino oscillation data are compatible with tri-bimaximal mixing, to leading order. The addition of an A₄ family symmetry and extended Higgs sector to the Standard Model can generate this mixing pattern, assuming the correct vacuum expectation value alignment of Higgs scalars. The effect of deviating this alignment is studied, for different types of A₄ models, with a phenomenological emphasis: the effect of perturbations on the model predictions for the neutrino oscillation and neutrino mass observables. The standard theoretical description of neutrino oscillations is presented, along with a summary of the past, present and future experimental efforts aimed at measuring the neutrino mixing parameters. Additionally, the current constraints on the sum of absolute neutrino masses and the amplitude for neutrinoless double beta decay, which is yet to be observed, are discussed. These constraints provide a model-independent test of family symmetery models. The Standard Model is reviewed, and extensions to the Standard Model such as the seesaw mechanism(s) are discussed: these are designed to endow neutrinos with mass, and can be incorporated into A₄ symmetry models. Models with different A₄ particle assignments are analysed for deviations from tribimaximal mixing. There are nine models presented in Chapter 5, with lepton doublets transforming as 3 (underlined) and right-handed charged leptons transforming as 1, 1', 1" (all underlined) ; five of these include right-handed neutrinos transforming as 3 (underlined) and make use of the seesaw mechanism. Chapter 6 contains the analysis of six models that assign all leptons to the 3 (underlined) representation, with four of these utilising the seesaw mechanism. The models are tested for any degree of fine tuning of the parameters that define the mass matrices. The effect of perturbations on the mixing angle observables, in particular sin² ∅₁₃ and sin² ∅₂₃, is studied, as well as the effect on the Jarlskog invariant, Jcp. Investigations of the (Mee)- ∑Mv parameter space allow for comparison with current data, and can lead to the possible exclusion of a particular model by constraints from future data.
- Full Text:
- Date Issued: 2010
- Authors: Barry, James Munnik Hamilton
- Date: 2010
- Subjects: Neutrinos -- Mass , Standard model (Nuclear physics) , Particles (Nuclear physics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5554 , http://hdl.handle.net/10962/d1015271
- Description: The present neutrino oscillation data are compatible with tri-bimaximal mixing, to leading order. The addition of an A₄ family symmetry and extended Higgs sector to the Standard Model can generate this mixing pattern, assuming the correct vacuum expectation value alignment of Higgs scalars. The effect of deviating this alignment is studied, for different types of A₄ models, with a phenomenological emphasis: the effect of perturbations on the model predictions for the neutrino oscillation and neutrino mass observables. The standard theoretical description of neutrino oscillations is presented, along with a summary of the past, present and future experimental efforts aimed at measuring the neutrino mixing parameters. Additionally, the current constraints on the sum of absolute neutrino masses and the amplitude for neutrinoless double beta decay, which is yet to be observed, are discussed. These constraints provide a model-independent test of family symmetery models. The Standard Model is reviewed, and extensions to the Standard Model such as the seesaw mechanism(s) are discussed: these are designed to endow neutrinos with mass, and can be incorporated into A₄ symmetry models. Models with different A₄ particle assignments are analysed for deviations from tribimaximal mixing. There are nine models presented in Chapter 5, with lepton doublets transforming as 3 (underlined) and right-handed charged leptons transforming as 1, 1', 1" (all underlined) ; five of these include right-handed neutrinos transforming as 3 (underlined) and make use of the seesaw mechanism. Chapter 6 contains the analysis of six models that assign all leptons to the 3 (underlined) representation, with four of these utilising the seesaw mechanism. The models are tested for any degree of fine tuning of the parameters that define the mass matrices. The effect of perturbations on the mixing angle observables, in particular sin² ∅₁₃ and sin² ∅₂₃, is studied, as well as the effect on the Jarlskog invariant, Jcp. Investigations of the (Mee)- ∑Mv parameter space allow for comparison with current data, and can lead to the possible exclusion of a particular model by constraints from future data.
- Full Text:
- Date Issued: 2010
A feasibility study into the possibility of ionospheric propagation of low VHF (30-35 MHZ) signals between South Africa and Central Africa
- Authors: Coetzee, Petrus Johannes
- Date: 2009
- Subjects: Communications, Military -- South Africa , Communications, Military -- Africa, Central , Digital communications -- South Africa , Digital communications -- Africa, Central , Signals and signaling -- South Africa , Signals and signaling -- Africa, Central , Artificial satellites in telecommunication -- South Africa , Artificial satellites in telecommunication -- Africa, Central , Shortwave radio
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5465 , http://hdl.handle.net/10962/d1005250 , Communications, Military -- South Africa , Communications, Military -- Africa, Central , Digital communications -- South Africa , Digital communications -- Africa, Central , Signals and signaling -- South Africa , Signals and signaling -- Africa, Central , Artificial satellites in telecommunication -- South Africa , Artificial satellites in telecommunication -- Africa, Central , Shortwave radio
- Description: The role of the South African National Defence Force (SANDF) has changed considerably in the last decade. The emphasis has moved from protecting the country's borders to peacekeeping duties in Central Africa and even further North. Communications between the peacekeeping missions and the military bases back in South Africa is vital to ensure the success of these missions. Currently use is made of satellite as well as High Frequency (HF) communications. There are drawbacks associated with these technologies (high cost and low data rates/interference respectively). Successful long distance ionospheric propagation in the low Very High Frequency (VHF) range will complement the existing infrastructure and enhance the success rate of these missions. This thesis presents a feasibility study to determine under what ionospheric conditions such low VHF communications will be possible. The International Reference Ionosphere (IRI) was used to generate ionospheric data for the reflection point(s) of the signal. The peak height of the ionospheric F2 layer (hmF2) was used to calculate the required antenna elevation angle. Once the elevation angle is known it is possible to calculate the required F2 layer critical frequency (foF2). The required foF2 value was calculated by assuming a Maximum Useable Frequency (MUF) of 20% higher than the planned operational frequency. It was determined that single hop propagation is possible during the daytime if the smoothed sunspot number (SSN) exceeds 15. The most challenging requirement for successful single hop propagation is the need of an antenna height of 23 m. For rapid deployment and semi-mobile operations within a jungle environment it may prove to be a formidable obstacle.
- Full Text:
- Date Issued: 2009
- Authors: Coetzee, Petrus Johannes
- Date: 2009
- Subjects: Communications, Military -- South Africa , Communications, Military -- Africa, Central , Digital communications -- South Africa , Digital communications -- Africa, Central , Signals and signaling -- South Africa , Signals and signaling -- Africa, Central , Artificial satellites in telecommunication -- South Africa , Artificial satellites in telecommunication -- Africa, Central , Shortwave radio
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5465 , http://hdl.handle.net/10962/d1005250 , Communications, Military -- South Africa , Communications, Military -- Africa, Central , Digital communications -- South Africa , Digital communications -- Africa, Central , Signals and signaling -- South Africa , Signals and signaling -- Africa, Central , Artificial satellites in telecommunication -- South Africa , Artificial satellites in telecommunication -- Africa, Central , Shortwave radio
- Description: The role of the South African National Defence Force (SANDF) has changed considerably in the last decade. The emphasis has moved from protecting the country's borders to peacekeeping duties in Central Africa and even further North. Communications between the peacekeeping missions and the military bases back in South Africa is vital to ensure the success of these missions. Currently use is made of satellite as well as High Frequency (HF) communications. There are drawbacks associated with these technologies (high cost and low data rates/interference respectively). Successful long distance ionospheric propagation in the low Very High Frequency (VHF) range will complement the existing infrastructure and enhance the success rate of these missions. This thesis presents a feasibility study to determine under what ionospheric conditions such low VHF communications will be possible. The International Reference Ionosphere (IRI) was used to generate ionospheric data for the reflection point(s) of the signal. The peak height of the ionospheric F2 layer (hmF2) was used to calculate the required antenna elevation angle. Once the elevation angle is known it is possible to calculate the required F2 layer critical frequency (foF2). The required foF2 value was calculated by assuming a Maximum Useable Frequency (MUF) of 20% higher than the planned operational frequency. It was determined that single hop propagation is possible during the daytime if the smoothed sunspot number (SSN) exceeds 15. The most challenging requirement for successful single hop propagation is the need of an antenna height of 23 m. For rapid deployment and semi-mobile operations within a jungle environment it may prove to be a formidable obstacle.
- Full Text:
- Date Issued: 2009
A real time HF beacon monitoring station for South Africa
- Authors: Mudzingwa, Courage
- Date: 2009
- Subjects: Radio , Shortwave radio , Radio and television towers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5486 , http://hdl.handle.net/10962/d1005272 , Radio , Shortwave radio , Radio and television towers
- Description: High frequency, HF (3 - 30 MHz), radio communications are greatly affected by ionospheric conditions. Both civilian and military users need reliable, real time propagation information to show at any time the feasibility of communicating to any part of the world on a particular frequency band. For this thesis, an automated receiving/monitoring station for the Northern California DX Foundation (NCDXF)/ International Amateur Radio Union (IARU) International Beacon Project was setup at the Hermanus Magnetic Observatory, HMO (34.42oS, 19.22oE) to monitor international beacons on 20 m, 17 m, 15 m, 12 m and 10 m bands. The beacons form a world wide multiband network. The task of monitoring the beacons was broken down into two steps. Initially the single band station, at 14.10 MHz, was installed and later it was upgraded to a multiband station capable of automatically monitoring all the five HF bands. The single band station setup involved the construction and installation of the half-wave dipole antenna, construction and installation of an HF choke balun; and the choice of Faros 1.3 as the appropriate monitoring software. The multiband monitoring station set-up involved the installation of an MFJ-1778 G5RV multiband antenna, construction and installation of a Communication Interface - V (CI-V) level converter and configuring the Faros 1.3 software to monitor the beacons on all five HF bands. Then a web page was created on the HMO space weather website (http://spaceweather.hmo.ac.za). Here, the real-time signal to noise ratio (SNR) and short path (SP)/long path (LP) plots are uploaded every 3 minutes, showing real time HF propagation conditions on the five HF bands. Historical propagation data are archived for later analysis. A preliminary data analysis was done to confirm the peration of the monitoring station. The archived data were analysed and compared to ICEPAC (Ionospheric Communications Enhanced Profile Analysis and Circuit) predictions. Results show that the real-time signal plots as well as the archive of historical signal plots, convey information on ropagation conditions to users in terms that are easy to interpret and understand.
- Full Text:
- Date Issued: 2009
- Authors: Mudzingwa, Courage
- Date: 2009
- Subjects: Radio , Shortwave radio , Radio and television towers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5486 , http://hdl.handle.net/10962/d1005272 , Radio , Shortwave radio , Radio and television towers
- Description: High frequency, HF (3 - 30 MHz), radio communications are greatly affected by ionospheric conditions. Both civilian and military users need reliable, real time propagation information to show at any time the feasibility of communicating to any part of the world on a particular frequency band. For this thesis, an automated receiving/monitoring station for the Northern California DX Foundation (NCDXF)/ International Amateur Radio Union (IARU) International Beacon Project was setup at the Hermanus Magnetic Observatory, HMO (34.42oS, 19.22oE) to monitor international beacons on 20 m, 17 m, 15 m, 12 m and 10 m bands. The beacons form a world wide multiband network. The task of monitoring the beacons was broken down into two steps. Initially the single band station, at 14.10 MHz, was installed and later it was upgraded to a multiband station capable of automatically monitoring all the five HF bands. The single band station setup involved the construction and installation of the half-wave dipole antenna, construction and installation of an HF choke balun; and the choice of Faros 1.3 as the appropriate monitoring software. The multiband monitoring station set-up involved the installation of an MFJ-1778 G5RV multiband antenna, construction and installation of a Communication Interface - V (CI-V) level converter and configuring the Faros 1.3 software to monitor the beacons on all five HF bands. Then a web page was created on the HMO space weather website (http://spaceweather.hmo.ac.za). Here, the real-time signal to noise ratio (SNR) and short path (SP)/long path (LP) plots are uploaded every 3 minutes, showing real time HF propagation conditions on the five HF bands. Historical propagation data are archived for later analysis. A preliminary data analysis was done to confirm the peration of the monitoring station. The archived data were analysed and compared to ICEPAC (Ionospheric Communications Enhanced Profile Analysis and Circuit) predictions. Results show that the real-time signal plots as well as the archive of historical signal plots, convey information on ropagation conditions to users in terms that are easy to interpret and understand.
- Full Text:
- Date Issued: 2009
Developing an ionospheric map for South Africa
- Authors: Okoh, Daniel Izuikeninachi
- Date: 2009
- Subjects: Ionosphere -- South Africa , Shortwave radio , Ionospheric electron density -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5459 , http://hdl.handle.net/10962/d1005244 , Ionosphere -- South Africa , Shortwave radio , Ionospheric electron density -- South Africa
- Description: This thesis describes the development of an ionospheric map for the South African region using the current available resources. The International Reference Ionosphere (IRI) model, the South African Bottomside Ionospheric Model (SABIM), and measurements from ionosondes in the South African Ionosonde Network, were incorporated into the map. An accurate ionospheric map depicting the foF2 and hmF2 parameters as well as electron density profiles at any location within South Africa is a useful tool for, amongst others, High Frequency (HF) communicators and space weather centers. A major product of the work is software, written in MATLAB, which produces spatial and temporal representations of the South African ionosphere. The map was validated and demonstrated for practical application, since a significant aim of the project was to make the map as applicable as possible. It is hoped that the map will find immense application in HF radio communication industries, research industries, aviation industries, and other industries that make use of Earth-Space systems. A potential user of the map is GrinTek Ewation (GEW) who is currently evaluating it for their purposes
- Full Text:
- Date Issued: 2009
- Authors: Okoh, Daniel Izuikeninachi
- Date: 2009
- Subjects: Ionosphere -- South Africa , Shortwave radio , Ionospheric electron density -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5459 , http://hdl.handle.net/10962/d1005244 , Ionosphere -- South Africa , Shortwave radio , Ionospheric electron density -- South Africa
- Description: This thesis describes the development of an ionospheric map for the South African region using the current available resources. The International Reference Ionosphere (IRI) model, the South African Bottomside Ionospheric Model (SABIM), and measurements from ionosondes in the South African Ionosonde Network, were incorporated into the map. An accurate ionospheric map depicting the foF2 and hmF2 parameters as well as electron density profiles at any location within South Africa is a useful tool for, amongst others, High Frequency (HF) communicators and space weather centers. A major product of the work is software, written in MATLAB, which produces spatial and temporal representations of the South African ionosphere. The map was validated and demonstrated for practical application, since a significant aim of the project was to make the map as applicable as possible. It is hoped that the map will find immense application in HF radio communication industries, research industries, aviation industries, and other industries that make use of Earth-Space systems. A potential user of the map is GrinTek Ewation (GEW) who is currently evaluating it for their purposes
- Full Text:
- Date Issued: 2009
Development of a neural network based model for predicting the occurrence of spread F within the Brazilian sector
- Authors: Paradza, Masimba Wellington
- Date: 2009
- Subjects: Neural networks (Computer science) , Ionosphere , F region
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5460 , http://hdl.handle.net/10962/d1005245 , Neural networks (Computer science) , Ionosphere , F region
- Description: Spread F is a phenomenon of the ionosphere in which the pulses returned from the ionosphere are of a much greater duration than the transmitted ones. The occurrence of spread F can be predicted using the technique of Neural Networks (NNs). This thesis presents the development and evaluation of NN based models (two single station models and a regional model) for predicting the occurrence of spread F over selected stations within the Brazilian sector. The input space for the NNs included the day number (seasonal variation), hour (diurnal variation), sunspot number (measure of the solar activity), magnetic index (measure of the magnetic activity) and magnetic position (latitude, magnetic declination and inclination). Twelve years of spread F data measured during 1978 to 1989 inclusively at the equatorial site Fortaleza and low latitude site Cachoeira Paulista are used in the development of an input space and NN architecture for the NN models. Spread F data that is believed to be related to plasma bubble developments (range spread F) were used in the development of the models while those associated with narrow spectrum irregularities that occur near the F layer (frequency spread F) were excluded. The results of the models show the dependency of the probability of spread F as a function of local time, season and latitude. The models also illustrate some characteristics of spread F such as the onset and peak occurrence of spread F as a function of distance from the equator. Results from these models are presented in this thesis and compared to measured data and to modelled data obtained with an empirical model developed for the same purpose.
- Full Text:
- Date Issued: 2009
- Authors: Paradza, Masimba Wellington
- Date: 2009
- Subjects: Neural networks (Computer science) , Ionosphere , F region
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5460 , http://hdl.handle.net/10962/d1005245 , Neural networks (Computer science) , Ionosphere , F region
- Description: Spread F is a phenomenon of the ionosphere in which the pulses returned from the ionosphere are of a much greater duration than the transmitted ones. The occurrence of spread F can be predicted using the technique of Neural Networks (NNs). This thesis presents the development and evaluation of NN based models (two single station models and a regional model) for predicting the occurrence of spread F over selected stations within the Brazilian sector. The input space for the NNs included the day number (seasonal variation), hour (diurnal variation), sunspot number (measure of the solar activity), magnetic index (measure of the magnetic activity) and magnetic position (latitude, magnetic declination and inclination). Twelve years of spread F data measured during 1978 to 1989 inclusively at the equatorial site Fortaleza and low latitude site Cachoeira Paulista are used in the development of an input space and NN architecture for the NN models. Spread F data that is believed to be related to plasma bubble developments (range spread F) were used in the development of the models while those associated with narrow spectrum irregularities that occur near the F layer (frequency spread F) were excluded. The results of the models show the dependency of the probability of spread F as a function of local time, season and latitude. The models also illustrate some characteristics of spread F such as the onset and peak occurrence of spread F as a function of distance from the equator. Results from these models are presented in this thesis and compared to measured data and to modelled data obtained with an empirical model developed for the same purpose.
- Full Text:
- Date Issued: 2009
Forecasting solar cycle 24 using neural networks
- Authors: Uwamahoro, Jean
- Date: 2009
- Subjects: Solar cycle , Neural networks (Computer science) , Ionosphere , Ionospheric electron density , Ionospheric forecasting , Solar thermal energy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5468 , http://hdl.handle.net/10962/d1005253 , Solar cycle , Neural networks (Computer science) , Ionosphere , Ionospheric electron density , Ionospheric forecasting , Solar thermal energy
- Description: The ability to predict the future behavior of solar activity has become of extreme importance due to its effect on the near-Earth environment. Predictions of both the amplitude and timing of the next solar cycle will assist in estimating the various consequences of Space Weather. Several prediction techniques have been applied and have achieved varying degrees of success in the domain of solar activity prediction. These techniques include, for example, neural networks and geomagnetic precursor methods. In this thesis, various neural network based models were developed and the model considered to be optimum was used to estimate the shape and timing of solar cycle 24. Given the recent success of the geomagnetic precusrsor methods, geomagnetic activity as measured by the aa index is considered among the main inputs to the neural network model. The neural network model developed is also provided with the time input parameters defining the year and the month of a particular solar cycle, in order to characterise the temporal behaviour of sunspot number as observed during the last 10 solar cycles. The structure of input-output patterns to the neural network is constructed in such a way that the network learns the relationship between the aa index values of a particular cycle, and the sunspot number values of the following cycle. Assuming January 2008 as the minimum preceding solar cycle 24, the shape and amplitude of solar cycle 24 is estimated in terms of monthly mean and smoothed monthly sunspot number. This new prediction model estimates an average solar cycle 24, with the maximum occurring around June 2012 [± 11 months], with a smoothed monthly maximum sunspot number of 121 ± 9.
- Full Text:
- Date Issued: 2009
- Authors: Uwamahoro, Jean
- Date: 2009
- Subjects: Solar cycle , Neural networks (Computer science) , Ionosphere , Ionospheric electron density , Ionospheric forecasting , Solar thermal energy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5468 , http://hdl.handle.net/10962/d1005253 , Solar cycle , Neural networks (Computer science) , Ionosphere , Ionospheric electron density , Ionospheric forecasting , Solar thermal energy
- Description: The ability to predict the future behavior of solar activity has become of extreme importance due to its effect on the near-Earth environment. Predictions of both the amplitude and timing of the next solar cycle will assist in estimating the various consequences of Space Weather. Several prediction techniques have been applied and have achieved varying degrees of success in the domain of solar activity prediction. These techniques include, for example, neural networks and geomagnetic precursor methods. In this thesis, various neural network based models were developed and the model considered to be optimum was used to estimate the shape and timing of solar cycle 24. Given the recent success of the geomagnetic precusrsor methods, geomagnetic activity as measured by the aa index is considered among the main inputs to the neural network model. The neural network model developed is also provided with the time input parameters defining the year and the month of a particular solar cycle, in order to characterise the temporal behaviour of sunspot number as observed during the last 10 solar cycles. The structure of input-output patterns to the neural network is constructed in such a way that the network learns the relationship between the aa index values of a particular cycle, and the sunspot number values of the following cycle. Assuming January 2008 as the minimum preceding solar cycle 24, the shape and amplitude of solar cycle 24 is estimated in terms of monthly mean and smoothed monthly sunspot number. This new prediction model estimates an average solar cycle 24, with the maximum occurring around June 2012 [± 11 months], with a smoothed monthly maximum sunspot number of 121 ± 9.
- Full Text:
- Date Issued: 2009
Geomagnetically induced current characteristics in southern Africa
- Authors: Ngwira, Chigomezyo Mudala
- Date: 2009
- Subjects: Magnetic Observatory (South African Council for Scientific and Industrial Research) Geomagnetism -- Africa,Southern Computer networks -- Africa, Southern Magnetospheric currents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5469 , http://hdl.handle.net/10962/d1005254
- Description: Geomagnetically induced currents (GICs), resulting from adverse space weather, have been demonstrated to cause damage to power transformers at mid-latitudes. There is growing concern over possible GIC effects in the Southern African network due to its long power lines. Previous efforts to model the electric field associated with GICs in the Southern Africa region used a uniform ground conductivity model. In an effort to improve the modelling of GICs, GIC data together with Hermanus Magnetic Observatory geomagnetic field data were used to obtain a multilayered ground conductivity model. This process requires a definition of the network coefficients, which are then used in subsequent calculations. This study shows that GIC computed with the new network coefficients and the multilayered ground conductivity model improves the accuracy of GIC modelling. Then GIC statistics are derived based on the recordings of the geomagnetic field at Hermanus, the new network coefficients and ground conductivity model. The geoelectric field is modelled using the plane wave method. The properties of the geomagnetic field, their time derivatives and local geomagnetic indices were investigated to determine their characteristics in relation to the GIC. The pattern of the time derivatives of the horizontal geomagnetic field closely follow the rate of change of the north-south geomagnetic component rather than the east-west component. The correlation between the GIC and the local geomagnetic field indices was also investigated. The results show that there is a higher correlation between the GIC and the east-west components of the geomagnetic local indices than between the GIC and the north-south components. This corresponds very well with the orientation of the power lines feeding the power transformers at the South African Grassridge electrical substation GIC site. Thus, the geoelectric field driving the GIC at Grassridge is north-south oriented. Further, it is shown that the geomagnetic observation sites have a strong directional preference with respect to the Grassridge GIC site.
- Full Text:
- Date Issued: 2009
- Authors: Ngwira, Chigomezyo Mudala
- Date: 2009
- Subjects: Magnetic Observatory (South African Council for Scientific and Industrial Research) Geomagnetism -- Africa,Southern Computer networks -- Africa, Southern Magnetospheric currents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5469 , http://hdl.handle.net/10962/d1005254
- Description: Geomagnetically induced currents (GICs), resulting from adverse space weather, have been demonstrated to cause damage to power transformers at mid-latitudes. There is growing concern over possible GIC effects in the Southern African network due to its long power lines. Previous efforts to model the electric field associated with GICs in the Southern Africa region used a uniform ground conductivity model. In an effort to improve the modelling of GICs, GIC data together with Hermanus Magnetic Observatory geomagnetic field data were used to obtain a multilayered ground conductivity model. This process requires a definition of the network coefficients, which are then used in subsequent calculations. This study shows that GIC computed with the new network coefficients and the multilayered ground conductivity model improves the accuracy of GIC modelling. Then GIC statistics are derived based on the recordings of the geomagnetic field at Hermanus, the new network coefficients and ground conductivity model. The geoelectric field is modelled using the plane wave method. The properties of the geomagnetic field, their time derivatives and local geomagnetic indices were investigated to determine their characteristics in relation to the GIC. The pattern of the time derivatives of the horizontal geomagnetic field closely follow the rate of change of the north-south geomagnetic component rather than the east-west component. The correlation between the GIC and the local geomagnetic field indices was also investigated. The results show that there is a higher correlation between the GIC and the east-west components of the geomagnetic local indices than between the GIC and the north-south components. This corresponds very well with the orientation of the power lines feeding the power transformers at the South African Grassridge electrical substation GIC site. Thus, the geoelectric field driving the GIC at Grassridge is north-south oriented. Further, it is shown that the geomagnetic observation sites have a strong directional preference with respect to the Grassridge GIC site.
- Full Text:
- Date Issued: 2009
Predictability of Geomagnetically Induced Currents using neural networks
- Authors: Lotz, Stefan
- Date: 2009
- Subjects: Advanced Composition Explorer (Artificial satellite) , Geomagnetism , Electromagnetic induction , Neural networks (Computer science) , Artificial intelligence
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5483 , http://hdl.handle.net/10962/d1005269 , Advanced Composition Explorer (Artificial satellite) , Geomagnetism , Electromagnetic induction , Neural networks (Computer science) , Artificial intelligence
- Description: It is a well documented fact that Geomagnetically Induced Currents (GIC’s) poses a significant threat to ground-based electric conductor networks like oil pipelines, railways and powerline networks. A study is undertaken to determine the feasibility of using artificial neural network models to predict GIC occurrence in the Southern African power grid. The magnitude of an induced current at a specific location on the Earth’s surface is directly related to the temporal derivative of the geomagnetic field (specifically its horizontal components) at that point. Hence, the focus of the problem is on the prediction of the temporal variations in the horizontal geomagnetic field (@Bx/@t and @By/@t). Artificial neural networks are used to predict @Bx/@t and @By/@t measured at Hermanus, South Africa (34.27◦ S, 19.12◦ E) with a 30 minute prediction lead time. As input parameters to the neural networks, insitu solar wind measurements made by the Advanced Composition Explorer (ACE) satellite are used. The results presented here compare well with similar models developed at high-latitude locations (e.g. Sweden, Finland, Canada) where extensive GIC research has been undertaken. It is concluded that it would indeed be feasible to use a neural network model to predict GIC occurrence in the Southern African power grid, provided that GIC measurements, powerline configuration and network parameters are made available.
- Full Text:
- Date Issued: 2009
- Authors: Lotz, Stefan
- Date: 2009
- Subjects: Advanced Composition Explorer (Artificial satellite) , Geomagnetism , Electromagnetic induction , Neural networks (Computer science) , Artificial intelligence
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5483 , http://hdl.handle.net/10962/d1005269 , Advanced Composition Explorer (Artificial satellite) , Geomagnetism , Electromagnetic induction , Neural networks (Computer science) , Artificial intelligence
- Description: It is a well documented fact that Geomagnetically Induced Currents (GIC’s) poses a significant threat to ground-based electric conductor networks like oil pipelines, railways and powerline networks. A study is undertaken to determine the feasibility of using artificial neural network models to predict GIC occurrence in the Southern African power grid. The magnitude of an induced current at a specific location on the Earth’s surface is directly related to the temporal derivative of the geomagnetic field (specifically its horizontal components) at that point. Hence, the focus of the problem is on the prediction of the temporal variations in the horizontal geomagnetic field (@Bx/@t and @By/@t). Artificial neural networks are used to predict @Bx/@t and @By/@t measured at Hermanus, South Africa (34.27◦ S, 19.12◦ E) with a 30 minute prediction lead time. As input parameters to the neural networks, insitu solar wind measurements made by the Advanced Composition Explorer (ACE) satellite are used. The results presented here compare well with similar models developed at high-latitude locations (e.g. Sweden, Finland, Canada) where extensive GIC research has been undertaken. It is concluded that it would indeed be feasible to use a neural network model to predict GIC occurrence in the Southern African power grid, provided that GIC measurements, powerline configuration and network parameters are made available.
- Full Text:
- Date Issued: 2009
Variability analysis of a sample of potential southern calibration sources
- Authors: Hungwe, Faith
- Date: 2009
- Subjects: Southern sky (Astronomy) Radio sources (Astronomy) Active galactic nuclei Very Long Baseline Array (Telescopes) Calibration Radio telescopes -- Southern Hemisphere Radio astronomy -- Southern Hemisphere Radio interferometers Very long baseline interferometry Radio astronomy -- Observations Radio astronomy -- South Africa Radio telescopes -- South Africa Square Kilometer Array (Spacecraft)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5495 , http://hdl.handle.net/10962/d1005281
- Description: A considerable number of Very Long Baseline Interferometry (VLBI) surveys have been conducted in the northern hemisphere and very few in the southern hemisphere mostly because of a lack of telescopes and therefore adequate baseline coverage. Thus there is a deficit of calibrator sources in the southern hemisphere. Further, some of the most interesting astronomical objects eg. the galactic centre and the nearest galaxies (the small and large Magellanic Clouds) lie in the southern hemisphere and these require high resolution studies. With a major expansion of radio astronomy observing capability on its way in the southern hemisphere (with the two SKA (Square Kilometre Array) precursors, meerKAT (Karoo Array Telescope) and ASKAP (Australian SKA Pathfinder), leading to the SKA itself) it is clear that interferometry and VLBI in the southern hemisphere need a dense network of calibration sources at different resolutions and a range of frequencies. This work seeks to help redress this problem by presenting an analysis of 31 southern sources to help fill the gaps in the southern hemisphere calibrator distribution. We have developed a multi-parameter method of classifying these sources as calibrators. From our sample of 31 sources, we have 2 class A sources (Excellent calibrators), 16 class B sources (Good calibrators), 9 class C sources (Poor calibrators) and 4 class D sources (Unsuitable calibrators).
- Full Text:
- Date Issued: 2009
- Authors: Hungwe, Faith
- Date: 2009
- Subjects: Southern sky (Astronomy) Radio sources (Astronomy) Active galactic nuclei Very Long Baseline Array (Telescopes) Calibration Radio telescopes -- Southern Hemisphere Radio astronomy -- Southern Hemisphere Radio interferometers Very long baseline interferometry Radio astronomy -- Observations Radio astronomy -- South Africa Radio telescopes -- South Africa Square Kilometer Array (Spacecraft)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5495 , http://hdl.handle.net/10962/d1005281
- Description: A considerable number of Very Long Baseline Interferometry (VLBI) surveys have been conducted in the northern hemisphere and very few in the southern hemisphere mostly because of a lack of telescopes and therefore adequate baseline coverage. Thus there is a deficit of calibrator sources in the southern hemisphere. Further, some of the most interesting astronomical objects eg. the galactic centre and the nearest galaxies (the small and large Magellanic Clouds) lie in the southern hemisphere and these require high resolution studies. With a major expansion of radio astronomy observing capability on its way in the southern hemisphere (with the two SKA (Square Kilometre Array) precursors, meerKAT (Karoo Array Telescope) and ASKAP (Australian SKA Pathfinder), leading to the SKA itself) it is clear that interferometry and VLBI in the southern hemisphere need a dense network of calibration sources at different resolutions and a range of frequencies. This work seeks to help redress this problem by presenting an analysis of 31 southern sources to help fill the gaps in the southern hemisphere calibrator distribution. We have developed a multi-parameter method of classifying these sources as calibrators. From our sample of 31 sources, we have 2 class A sources (Excellent calibrators), 16 class B sources (Good calibrators), 9 class C sources (Poor calibrators) and 4 class D sources (Unsuitable calibrators).
- Full Text:
- Date Issued: 2009
A feasibility study into total electron content prediction using neural networks
- Authors: Habarulema, John Bosco
- Date: 2008
- Subjects: Electrons , Neural networks (Computer science) , Global Positioning System , Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5466 , http://hdl.handle.net/10962/d1005251 , Electrons , Neural networks (Computer science) , Global Positioning System , Ionosphere , Ionospheric electron density
- Description: Global Positioning System (GPS) networks provide an opportunity to study the dynamics and continuous changes in the ionosphere by supplementing ionospheric measurements which are usually obtained by various techniques such as ionosondes, incoherent scatter radars and satellites. Total electron content (TEC) is one of the physical quantities that can be derived from GPS data, and provides an indication of ionospheric variability. This thesis presents a feasibility study for the development of a Neural Network (NN) based model for the prediction of South African GPS derived TEC. The South African GPS receiver network is operated and maintained by the Chief Directorate Surveys and Mapping (CDSM) in Cape Town, South Africa. Three South African locations were identified and used in the development of an input space and NN architecture for the model. The input space includes the day number (seasonal variation), hour (diurnal variation), sunspot number (measure of the solar activity), and magnetic index(measure of the magnetic activity). An attempt to study the effects of solar wind on TEC variability was carried out using the Advanced Composition Explorer (ACE) data and it is recommended that more study be done using low altitude satellite data. An analysis was done by comparing predicted NN TEC with TEC values from the IRI2001 version of the International Reference Ionosphere (IRI), validating GPS TEC with ionosonde TEC (ITEC) and assessing the performance of the NN model during equinoxes and solstices. Results show that NNs predict GPS TEC more accurately than the IRI at South African GPS locations, but that more good quality GPS data is required before a truly representative empirical GPS TEC model can be released.
- Full Text:
- Date Issued: 2008
- Authors: Habarulema, John Bosco
- Date: 2008
- Subjects: Electrons , Neural networks (Computer science) , Global Positioning System , Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5466 , http://hdl.handle.net/10962/d1005251 , Electrons , Neural networks (Computer science) , Global Positioning System , Ionosphere , Ionospheric electron density
- Description: Global Positioning System (GPS) networks provide an opportunity to study the dynamics and continuous changes in the ionosphere by supplementing ionospheric measurements which are usually obtained by various techniques such as ionosondes, incoherent scatter radars and satellites. Total electron content (TEC) is one of the physical quantities that can be derived from GPS data, and provides an indication of ionospheric variability. This thesis presents a feasibility study for the development of a Neural Network (NN) based model for the prediction of South African GPS derived TEC. The South African GPS receiver network is operated and maintained by the Chief Directorate Surveys and Mapping (CDSM) in Cape Town, South Africa. Three South African locations were identified and used in the development of an input space and NN architecture for the model. The input space includes the day number (seasonal variation), hour (diurnal variation), sunspot number (measure of the solar activity), and magnetic index(measure of the magnetic activity). An attempt to study the effects of solar wind on TEC variability was carried out using the Advanced Composition Explorer (ACE) data and it is recommended that more study be done using low altitude satellite data. An analysis was done by comparing predicted NN TEC with TEC values from the IRI2001 version of the International Reference Ionosphere (IRI), validating GPS TEC with ionosonde TEC (ITEC) and assessing the performance of the NN model during equinoxes and solstices. Results show that NNs predict GPS TEC more accurately than the IRI at South African GPS locations, but that more good quality GPS data is required before a truly representative empirical GPS TEC model can be released.
- Full Text:
- Date Issued: 2008
A VLBI study of OH masers in a proto-planetary nebula OH 0.9+1.3
- Authors: McAlpine, Kim
- Date: 2008
- Subjects: Very long baseline interferometry , Proto-planetary nebulae , Masers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5499 , http://hdl.handle.net/10962/d1005285 , Very long baseline interferometry , Proto-planetary nebulae , Masers
- Description: This thesis reports the calibration, imaging and analysis of one epoch of VLBA observations of the 1612 MHz OH maser emission from the protoplanetary nebula OH 0.9+1.3. These are the first polarisation VLBI observations of this source and the spatial morphology of the OH emission is resolved on this scale. Proto-planetary nebulae represent the transition phase in the evolution of stars between the asymptotic giant branch (AGB) phase and their emergence as planetary nebulae. A long-standing astronomical question is how the predominantly spherical circumstellar envelopes of AGB stars evolve into the bipolar and axisymmetric structures that are commonly observed in planetary nebula. Proto-planetary nebulae offer a unique opportunity to study this transformation process. The high-resolution VLBI maps produced in this thesis were used to investigate the morphology and kinematics of OH 0.9+1.3 with a view to gaining insight into the development of asymmetries in the circumstellar material. The OH maser emission of OH 0.9+1.3 has a double-peaked profile with one peak blue-shifted and the other red-shifted with respect to the stellar velocity. The total intensity maser maps demonstrate a considerable degree of asymmetry with the blue- and red-shifted emission located in spatially distinct regions of the envelope. The blue-shifted emission is distributed preferentially along an axis at a projected position angle of » 135± ( North through East). The morphology of this source is not consistent with the standard symmetric thin-shell model and an attempt to fit the traditional OH/IR kinematic model of a simple expanding shell to the maser components was found to be unsatisfactory. No definitive evidence of a bipolar outflow was observed either. The high degree of asymmetry observed in the source is consistent with its status as a proto-planetary nebula. The source was imaged in all four Stokes parameters and the fractional linear and circular polarisations of the maser components were derived from the Stokes parameter maps. In all except one of the components the total fractional polarisation was found to be low ( < 15%). The mean fractional linear and circular polarisation were calculated to be 5.54% and 7.11% respectively. The absence of an identifiable Zeeman pair in the Stokes V map prohibited the estimation of the magnetic field in the circumstellar envelope of this source.
- Full Text:
- Date Issued: 2008
- Authors: McAlpine, Kim
- Date: 2008
- Subjects: Very long baseline interferometry , Proto-planetary nebulae , Masers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5499 , http://hdl.handle.net/10962/d1005285 , Very long baseline interferometry , Proto-planetary nebulae , Masers
- Description: This thesis reports the calibration, imaging and analysis of one epoch of VLBA observations of the 1612 MHz OH maser emission from the protoplanetary nebula OH 0.9+1.3. These are the first polarisation VLBI observations of this source and the spatial morphology of the OH emission is resolved on this scale. Proto-planetary nebulae represent the transition phase in the evolution of stars between the asymptotic giant branch (AGB) phase and their emergence as planetary nebulae. A long-standing astronomical question is how the predominantly spherical circumstellar envelopes of AGB stars evolve into the bipolar and axisymmetric structures that are commonly observed in planetary nebula. Proto-planetary nebulae offer a unique opportunity to study this transformation process. The high-resolution VLBI maps produced in this thesis were used to investigate the morphology and kinematics of OH 0.9+1.3 with a view to gaining insight into the development of asymmetries in the circumstellar material. The OH maser emission of OH 0.9+1.3 has a double-peaked profile with one peak blue-shifted and the other red-shifted with respect to the stellar velocity. The total intensity maser maps demonstrate a considerable degree of asymmetry with the blue- and red-shifted emission located in spatially distinct regions of the envelope. The blue-shifted emission is distributed preferentially along an axis at a projected position angle of » 135± ( North through East). The morphology of this source is not consistent with the standard symmetric thin-shell model and an attempt to fit the traditional OH/IR kinematic model of a simple expanding shell to the maser components was found to be unsatisfactory. No definitive evidence of a bipolar outflow was observed either. The high degree of asymmetry observed in the source is consistent with its status as a proto-planetary nebula. The source was imaged in all four Stokes parameters and the fractional linear and circular polarisations of the maser components were derived from the Stokes parameter maps. In all except one of the components the total fractional polarisation was found to be low ( < 15%). The mean fractional linear and circular polarisation were calculated to be 5.54% and 7.11% respectively. The absence of an identifiable Zeeman pair in the Stokes V map prohibited the estimation of the magnetic field in the circumstellar envelope of this source.
- Full Text:
- Date Issued: 2008
Designing and implementing a new pulsar timer for the Hartebeesthoek Radio Astronomy Observatory
- Authors: Youthed, Andrew David
- Date: 2008
- Subjects: Astronomical observatories , Radio astronomy , Pulsars , Astronomical instruments , Reduced instruction set computers , Random access memory
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5458 , http://hdl.handle.net/10962/d1005243 , Astronomical observatories , Radio astronomy , Pulsars , Astronomical instruments , Reduced instruction set computers , Random access memory
- Description: This thesis outlines the design and implementation of a single channel, dual polarization pulsar timing instrument for the Hartebeesthoek Radio Astronomy Observatory (HartRAO). The new timer is designed to be an improved, temporary replacement for the existing device which has been in operation for over 20 years. The existing device is no longer reliable and is di±cult to maintain. The new pulsar timer is designed to provide improved functional- ity, higher sampling speed, greater pulse resolution, more °exibility and easier maintenance over the existing device. The new device is also designed to keeping changes to the observation system to a minimum until a full de-dispersion timer can be implemented at theobservatory. The design makes use of an 8-bit Reduced Instruction Set Computer (RISC) micro-processor with external Random Access Memory (RAM). The instrument includes an IEEE-488 subsystem for interfacing the pulsar timer to the observation computer system. The microcontroller software is written in assembler code to ensure optimal loop execution speed and deterministic code execution for the system. The design path is discussed and problems encountered during the design process are highlighted. Final testing of the new instrument indicates an improvement in the sam- pling rate of 13.6 times and a significant reduction in 60Hz interference over the existing instrument.
- Full Text:
- Date Issued: 2008
- Authors: Youthed, Andrew David
- Date: 2008
- Subjects: Astronomical observatories , Radio astronomy , Pulsars , Astronomical instruments , Reduced instruction set computers , Random access memory
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5458 , http://hdl.handle.net/10962/d1005243 , Astronomical observatories , Radio astronomy , Pulsars , Astronomical instruments , Reduced instruction set computers , Random access memory
- Description: This thesis outlines the design and implementation of a single channel, dual polarization pulsar timing instrument for the Hartebeesthoek Radio Astronomy Observatory (HartRAO). The new timer is designed to be an improved, temporary replacement for the existing device which has been in operation for over 20 years. The existing device is no longer reliable and is di±cult to maintain. The new pulsar timer is designed to provide improved functional- ity, higher sampling speed, greater pulse resolution, more °exibility and easier maintenance over the existing device. The new device is also designed to keeping changes to the observation system to a minimum until a full de-dispersion timer can be implemented at theobservatory. The design makes use of an 8-bit Reduced Instruction Set Computer (RISC) micro-processor with external Random Access Memory (RAM). The instrument includes an IEEE-488 subsystem for interfacing the pulsar timer to the observation computer system. The microcontroller software is written in assembler code to ensure optimal loop execution speed and deterministic code execution for the system. The design path is discussed and problems encountered during the design process are highlighted. Final testing of the new instrument indicates an improvement in the sam- pling rate of 13.6 times and a significant reduction in 60Hz interference over the existing instrument.
- Full Text:
- Date Issued: 2008
Temperature dependence of the HartRAO pointing model
- Authors: Copley, Charles Judd
- Date: 2008
- Subjects: Astronomical instruments , Observatories -- South Africa , Telescopes , Astronomical observatories , Astronomy -- Data processing , Antennas (Electronics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5491 , http://hdl.handle.net/10962/d1005277 , Astronomical instruments , Observatories -- South Africa , Telescopes , Astronomical observatories , Astronomy -- Data processing , Antennas (Electronics)
- Description: This thesis investigates control aspects of the Hartebeeshoek Radio Astronomy Observatory (HartRAO) antenna. The installation of a new 22 GHz receiver has required the pointing accuracy to be improved to less than 4 mdeg. The effect of thermal conditions on the the HartRAO antenna pointing offset is investigated using a variety of modelling techniques including simple geometric modelling, neural networks and Principal Component Analysis (PCA). Convincing results were obtained for the Declination pointing offset, where applying certain model predictions to observations resulted in an improvement in Declination pointing offset from 5.5 mdeg to 3.2 mdeg (≈50%). The Right Ascension pointing model was considerably less convincing with an improvement of approximately from 5.5 mdeg to 4.5 mdeg (≈20%) in the Right Ascension pointing offset. The Declination pointing offset can be modelled sufficiently well to reduce the pointing offset to less than 4 mdeg, however further investigation of the underlying causes is required for the Right Ascension pointing offset.
- Full Text:
- Date Issued: 2008
- Authors: Copley, Charles Judd
- Date: 2008
- Subjects: Astronomical instruments , Observatories -- South Africa , Telescopes , Astronomical observatories , Astronomy -- Data processing , Antennas (Electronics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5491 , http://hdl.handle.net/10962/d1005277 , Astronomical instruments , Observatories -- South Africa , Telescopes , Astronomical observatories , Astronomy -- Data processing , Antennas (Electronics)
- Description: This thesis investigates control aspects of the Hartebeeshoek Radio Astronomy Observatory (HartRAO) antenna. The installation of a new 22 GHz receiver has required the pointing accuracy to be improved to less than 4 mdeg. The effect of thermal conditions on the the HartRAO antenna pointing offset is investigated using a variety of modelling techniques including simple geometric modelling, neural networks and Principal Component Analysis (PCA). Convincing results were obtained for the Declination pointing offset, where applying certain model predictions to observations resulted in an improvement in Declination pointing offset from 5.5 mdeg to 3.2 mdeg (≈50%). The Right Ascension pointing model was considerably less convincing with an improvement of approximately from 5.5 mdeg to 4.5 mdeg (≈20%) in the Right Ascension pointing offset. The Declination pointing offset can be modelled sufficiently well to reduce the pointing offset to less than 4 mdeg, however further investigation of the underlying causes is required for the Right Ascension pointing offset.
- Full Text:
- Date Issued: 2008
The variability and predictability of the IRI shape parameters over Grahamstown, South Africa
- Authors: Chimidza, Oyapo
- Date: 2008
- Subjects: Ionosphere -- Mathematical models -- South Africa , Atmosphere, Upper -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5496 , http://hdl.handle.net/10962/d1005282 , Ionosphere -- Mathematical models -- South Africa , Atmosphere, Upper -- South Africa
- Description: The International Reference Ionosphere (IRI) shape parameters B0, B1, and D1 provide a representation of the shape of the F2 layer, the thickness of the F2 layer and the shape of the F1 layer of the ionosphere respectively. The aim of this study was to examine the variability of these parameters using Grahamstown, South Africa (33.3±S, 26.5±E) ionosonde data and determine their predictability by the IRI-2001 model. A further aim of this study was to investigate developing an alternative model for predicting these parameters. These parameters can be determined from electron density profiles that are inverted from ionograms recorded with an ionosonde. Data representing the B0, B1 and D1 parameters, with half hourly or hourly intervals, were scaled and deduced from the digital pulse sounder (DPS) ionosonde for the period April 1996 to December 2006. An analysis of the diurnal, seasonal, and solar variations of the behaviour of these parameters was undertaken for the years 2000, 2004 and 2005 using monthly medians. Comparisons between the observational results and that of the IRI model (IRI 2001 version) indicate that the IRI-2001 model does not accurately represent the diurnal and seasonal variation of the parameters. A preliminary model was thus developed using the technique of Neural Networks (NNs). All available data from the Grahamstown ionosonde from 1996 to 2006 were used in the training of the NNs and the prediction of the variation of the shape parameters. Inputs to the model were the day number, the hour of day, the solar activity and the magnetic index. Comparisons between the preliminary NN model and the IRI-2001 model indicated that the preliminary model was more accurate at the prediction of the parameters than the IRI-2001 model. This analysis showed the need to improve the existing IRI model or develop a new model for the South African region. This thesis describes the results from this feasibility study which show the variability and predictability of the IRI shape parameters.
- Full Text:
- Date Issued: 2008
- Authors: Chimidza, Oyapo
- Date: 2008
- Subjects: Ionosphere -- Mathematical models -- South Africa , Atmosphere, Upper -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5496 , http://hdl.handle.net/10962/d1005282 , Ionosphere -- Mathematical models -- South Africa , Atmosphere, Upper -- South Africa
- Description: The International Reference Ionosphere (IRI) shape parameters B0, B1, and D1 provide a representation of the shape of the F2 layer, the thickness of the F2 layer and the shape of the F1 layer of the ionosphere respectively. The aim of this study was to examine the variability of these parameters using Grahamstown, South Africa (33.3±S, 26.5±E) ionosonde data and determine their predictability by the IRI-2001 model. A further aim of this study was to investigate developing an alternative model for predicting these parameters. These parameters can be determined from electron density profiles that are inverted from ionograms recorded with an ionosonde. Data representing the B0, B1 and D1 parameters, with half hourly or hourly intervals, were scaled and deduced from the digital pulse sounder (DPS) ionosonde for the period April 1996 to December 2006. An analysis of the diurnal, seasonal, and solar variations of the behaviour of these parameters was undertaken for the years 2000, 2004 and 2005 using monthly medians. Comparisons between the observational results and that of the IRI model (IRI 2001 version) indicate that the IRI-2001 model does not accurately represent the diurnal and seasonal variation of the parameters. A preliminary model was thus developed using the technique of Neural Networks (NNs). All available data from the Grahamstown ionosonde from 1996 to 2006 were used in the training of the NNs and the prediction of the variation of the shape parameters. Inputs to the model were the day number, the hour of day, the solar activity and the magnetic index. Comparisons between the preliminary NN model and the IRI-2001 model indicated that the preliminary model was more accurate at the prediction of the parameters than the IRI-2001 model. This analysis showed the need to improve the existing IRI model or develop a new model for the South African region. This thesis describes the results from this feasibility study which show the variability and predictability of the IRI shape parameters.
- Full Text:
- Date Issued: 2008
Verification of Ionospheric tomography using MIDAS over Grahamstown, South Africa
- Authors: Katamzi, Zama Thobeka
- Date: 2008
- Subjects: Ionosphere -- Remote sensing -- South Africa , Atmosphere, Upper , Tomography -- Scientific applications -- South Africa , Global Positioning System
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5497 , http://hdl.handle.net/10962/d1005283 , Ionosphere -- Remote sensing -- South Africa , Atmosphere, Upper , Tomography -- Scientific applications -- South Africa , Global Positioning System
- Description: Global Positioning System (GPS) satellites and receivers are used to derive total electron content (TEC) from the time delay and phase advance of the radiowaves as they travels through the ionosphere. TEC is defined as the integralof the electron density along the satellite-receiver signal path. Electron densityprofiles can be determined from these TEC values using ionospheric tomographic inversion techniques such as Multi-Instrument Data Analysis System (MIDAS).This thesis reports on a study aimed at evaluating the suitability of ionospheric tomography as a tool to derive one-dimensional electron density profiles, using the MIDAS inversion algorithm over Grahamstown, South Africa (33.30◦S, 26.50◦E). The evaluation was done by using ionosonde data from the Louisvale (28.50◦S, 21.20◦E) and Madimbo (22.40◦S, 30.90◦E) stations to create empirical orthonormal functions (EOFs). These EOFs were used by MIDAS in the inversion process to describe the vertical variation of the electron density. Profiles derived from the MIDAS algorithm were compared with profiles obtained from the international Reference Ionosphere (IRI) 2001 model and with ionosonde profiles from the Grahamstown ionosonde station. The optimised MIDAS profiles show a good agreement with the Grahamstown ionosonde profiles. The South African Bottomside Ionospheric Model (SABIM) was used to set the limits within which MIDAS was producing accurate peak electron density (NmF2) values and to define accuracy in this project, with the understanding that the national model (SABIM) is currently the best model for the Grahamstown region. Analysis show that MIDAS produces accurate results during the winter season, which had the lowest root mean square (rms) error of 0.37×1011[e/m3] and an approximately 86% chance of producing NmF2 closer to the actual NmF2 value than the national model SABIM. MIDAS was found to also produce accurate NmF2 values at 12h00 UT, where an approximately 88% chance of producing an accurate NmF2 value, which may deviate from the measured value by 0.72×1011[e/m3], was determined. In conclusion, ionospheric tomographic inversion techniques show promise in the reconstruction of electron density profiles over South Africa, and are worth pursuing further in the future.
- Full Text:
- Date Issued: 2008
- Authors: Katamzi, Zama Thobeka
- Date: 2008
- Subjects: Ionosphere -- Remote sensing -- South Africa , Atmosphere, Upper , Tomography -- Scientific applications -- South Africa , Global Positioning System
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5497 , http://hdl.handle.net/10962/d1005283 , Ionosphere -- Remote sensing -- South Africa , Atmosphere, Upper , Tomography -- Scientific applications -- South Africa , Global Positioning System
- Description: Global Positioning System (GPS) satellites and receivers are used to derive total electron content (TEC) from the time delay and phase advance of the radiowaves as they travels through the ionosphere. TEC is defined as the integralof the electron density along the satellite-receiver signal path. Electron densityprofiles can be determined from these TEC values using ionospheric tomographic inversion techniques such as Multi-Instrument Data Analysis System (MIDAS).This thesis reports on a study aimed at evaluating the suitability of ionospheric tomography as a tool to derive one-dimensional electron density profiles, using the MIDAS inversion algorithm over Grahamstown, South Africa (33.30◦S, 26.50◦E). The evaluation was done by using ionosonde data from the Louisvale (28.50◦S, 21.20◦E) and Madimbo (22.40◦S, 30.90◦E) stations to create empirical orthonormal functions (EOFs). These EOFs were used by MIDAS in the inversion process to describe the vertical variation of the electron density. Profiles derived from the MIDAS algorithm were compared with profiles obtained from the international Reference Ionosphere (IRI) 2001 model and with ionosonde profiles from the Grahamstown ionosonde station. The optimised MIDAS profiles show a good agreement with the Grahamstown ionosonde profiles. The South African Bottomside Ionospheric Model (SABIM) was used to set the limits within which MIDAS was producing accurate peak electron density (NmF2) values and to define accuracy in this project, with the understanding that the national model (SABIM) is currently the best model for the Grahamstown region. Analysis show that MIDAS produces accurate results during the winter season, which had the lowest root mean square (rms) error of 0.37×1011[e/m3] and an approximately 86% chance of producing NmF2 closer to the actual NmF2 value than the national model SABIM. MIDAS was found to also produce accurate NmF2 values at 12h00 UT, where an approximately 88% chance of producing an accurate NmF2 value, which may deviate from the measured value by 0.72×1011[e/m3], was determined. In conclusion, ionospheric tomographic inversion techniques show promise in the reconstruction of electron density profiles over South Africa, and are worth pursuing further in the future.
- Full Text:
- Date Issued: 2008
Measuring the RFI environment of the South African SKA site
- Authors: Manners, Paul John
- Date: 2007
- Subjects: Radio telescopes , Radio telescopes -- South Africa , Radio astronomy , Radio astronomy -- South Africa , Square Kilometer Array (Spacecraft) , Radio -- Interference -- Measurement
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5474 , http://hdl.handle.net/10962/d1005259 , Radio telescopes , Radio telescopes -- South Africa , Radio astronomy , Radio astronomy -- South Africa , Square Kilometer Array (Spacecraft) , Radio -- Interference -- Measurement
- Description: The Square Kilometre Array (SKA) Project is an international effort to build the world’s largest radio telescope. It will be 100 times more sensitive than any other radio telescope currently in existence and will consist of thousands of dishes placed at baselines up to 3000 km. In addition to its increased sensitivity it will operate over a very wide frequency range (current specification is 100 MHz - 22 GHz) and will use frequency bands not primarily allocated to radio astronomy. Because of this the telescope needs to be located at a site with low levels of radio frequency interference (RFI). This implies a site that is remote and away from human activity. In bidding to host the SKA, South Africa was required to conduct an RFI survey at its proposed site for a period of 12 months. Apart from this core site, where more than half the SKA dishes may potentially be deployed, the measurement of remote sites in Southern Africa was also required. To conduct measurements at these sites, three mobile measurement systems were designed and built by the South African SKA Project. The design considerations, implementation and RFI measurements recorded during this campaign will be the focus for this dissertation.
- Full Text:
- Date Issued: 2007
- Authors: Manners, Paul John
- Date: 2007
- Subjects: Radio telescopes , Radio telescopes -- South Africa , Radio astronomy , Radio astronomy -- South Africa , Square Kilometer Array (Spacecraft) , Radio -- Interference -- Measurement
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5474 , http://hdl.handle.net/10962/d1005259 , Radio telescopes , Radio telescopes -- South Africa , Radio astronomy , Radio astronomy -- South Africa , Square Kilometer Array (Spacecraft) , Radio -- Interference -- Measurement
- Description: The Square Kilometre Array (SKA) Project is an international effort to build the world’s largest radio telescope. It will be 100 times more sensitive than any other radio telescope currently in existence and will consist of thousands of dishes placed at baselines up to 3000 km. In addition to its increased sensitivity it will operate over a very wide frequency range (current specification is 100 MHz - 22 GHz) and will use frequency bands not primarily allocated to radio astronomy. Because of this the telescope needs to be located at a site with low levels of radio frequency interference (RFI). This implies a site that is remote and away from human activity. In bidding to host the SKA, South Africa was required to conduct an RFI survey at its proposed site for a period of 12 months. Apart from this core site, where more than half the SKA dishes may potentially be deployed, the measurement of remote sites in Southern Africa was also required. To conduct measurements at these sites, three mobile measurement systems were designed and built by the South African SKA Project. The design considerations, implementation and RFI measurements recorded during this campaign will be the focus for this dissertation.
- Full Text:
- Date Issued: 2007