Development of a distributed optical fiber sensor for geological applications
- Authors: James, Jena
- Date: 2022-04
- Subjects: Polymers--Optical properties -- South Africa , Detectors—Materials
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/56156 , vital:55973
- Description: The purpose of the study was to develop a distributed optical fiber acoustic sensor for monitoring ground subsidence before collapse sinkholes form causing costly damage on infrastructure. Costs in excess of R1.3 billion have been incurred while dealing with sinkhole related measures in South Africa. Monitoring sinkholes and the presence of an early warning alert system can drastically reduce the impact, risk and cost caused by sudden ground collapse. A related goal was to construct a reliable collapse alert early warning system to facilitate disaster preparedness and avoid further damage from accidents. This was achieved by developing a spectroscopic shift monitoring algorithm which analysed changes in the subsurface vibration modes using ambient noise signals. For the first time to our knowledge, an optic fiber sensor with an early warning alarm, using ambient noise vibrations to detect and monitor sinkholes was developed at NMU. A polarisation-based, interferometric optical fiber seismic sensor was developed and compared to a commercial geophone. The fiber sensor exhibited superior performance in sensitivity, bandwidth, signal response and recovery times. The sensitivity of the optical fiber sensor was 0.47 rad/Pa surpassing the geophone sensitivity by 9.32%, and the bandwidth of 3.349kHz was 20 times greater for the optical fiber sensor. The fiber sensor was used to measure millisecond events as the impact duration of a bouncing ball was successfully obtained. It was used to detect sinkhole formation in the simulator model, designed. Ground collapse precursors were identified, and early warning alert was achieved using the spectral analysis algorithm, developed. The collapse precursor condition was identified as a functional combination of variations in the peak frequency, bandwidth and peak intensity. A distributed acoustic sensor was built to detect ambient noise induced subsurface signals. Vibrations were located along the 28km length of optical fiber with a relative error of 9.6%. The sensor demonstrated a frequency response range of 212.25Hz, an event distance precision of 224m with time resolution of 1.12µs, and a spatial resolution of 1km. The position of disturbance was measured within 300m of its actual point of 3.21km along the optical fiber. The results showed that distributed optical fiber sensing allows real-time monitoring of the subsurface over extended distances, using ambient noise signals. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: James, Jena
- Date: 2022-04
- Subjects: Polymers--Optical properties -- South Africa , Detectors—Materials
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/56156 , vital:55973
- Description: The purpose of the study was to develop a distributed optical fiber acoustic sensor for monitoring ground subsidence before collapse sinkholes form causing costly damage on infrastructure. Costs in excess of R1.3 billion have been incurred while dealing with sinkhole related measures in South Africa. Monitoring sinkholes and the presence of an early warning alert system can drastically reduce the impact, risk and cost caused by sudden ground collapse. A related goal was to construct a reliable collapse alert early warning system to facilitate disaster preparedness and avoid further damage from accidents. This was achieved by developing a spectroscopic shift monitoring algorithm which analysed changes in the subsurface vibration modes using ambient noise signals. For the first time to our knowledge, an optic fiber sensor with an early warning alarm, using ambient noise vibrations to detect and monitor sinkholes was developed at NMU. A polarisation-based, interferometric optical fiber seismic sensor was developed and compared to a commercial geophone. The fiber sensor exhibited superior performance in sensitivity, bandwidth, signal response and recovery times. The sensitivity of the optical fiber sensor was 0.47 rad/Pa surpassing the geophone sensitivity by 9.32%, and the bandwidth of 3.349kHz was 20 times greater for the optical fiber sensor. The fiber sensor was used to measure millisecond events as the impact duration of a bouncing ball was successfully obtained. It was used to detect sinkhole formation in the simulator model, designed. Ground collapse precursors were identified, and early warning alert was achieved using the spectral analysis algorithm, developed. The collapse precursor condition was identified as a functional combination of variations in the peak frequency, bandwidth and peak intensity. A distributed acoustic sensor was built to detect ambient noise induced subsurface signals. Vibrations were located along the 28km length of optical fiber with a relative error of 9.6%. The sensor demonstrated a frequency response range of 212.25Hz, an event distance precision of 224m with time resolution of 1.12µs, and a spatial resolution of 1km. The position of disturbance was measured within 300m of its actual point of 3.21km along the optical fiber. The results showed that distributed optical fiber sensing allows real-time monitoring of the subsurface over extended distances, using ambient noise signals. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2022
- Full Text:
- Date Issued: 2022-04
Marine Plastic Pollution
- Vilakazi, Bathobile Thandazile Unittah
- Authors: Vilakazi, Bathobile Thandazile Unittah
- Date: 2021-12
- Subjects: Waste minimization --Law and legislation -- South Africa , Plastic marine debris , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55605 , vital:53364
- Description: Human activities can alter the ordinary operation of Earth-system processes in such a way that it escalates risks in societies across the globe. One of the more visible human activities is the production, consumption and disposal of plastic items and/or materials, the consequences of which are borne by marine life. The dissertation is founded on the premise that conservation of the marine environment must be a priority for all States. States must take responsibility for the prevention of pollution of the marine environment and further take accountability where activities within their territory are causing pollution of the marine environment through the enforcement of legislative measures. The dissertation is drafted in a manner that aims to ultimately deduce whether the current pollution laws in South Africa adequately address marine plastic pollution (MPP). As such, Chapter Two relies on the regulatory position of MPP at the international level. Various legal instruments relating to marine pollution are expounded on such as the LOSC, MARPOL, London Convention and other regional instruments relating particularly to the African continent. The chapter aims to detail the most relevant global instruments that South Africa is a party to and which promote and mandate States parties to protect the marine environment through the implementation and enforcement of regulatory measures. The global measures either exclusively address MPP or provide general provisions for marine environment protection. Chapter Three and Four of the dissertation provide a critical analysis of the legal measures adopted at the national, provincial and local levels respectively to control, reduce and prevent pollution, including MPP. The Constitution of the Republic of South Africa, 1996 requires the national, provincial and local levels of government to co-operate with each other to provide ―effective, efficient, transparent, accountable and coherent governance‖. Therefore, it is essential for this study to investigate the regulation of MPP at all levels of government particularly when the programmes of the national and provincial government must be implemented by local government. The regulatory measures at these levels of government promote the protection of the environment and further prohibit the illegal dumping of waste and littering. They also encourage communities to reduce, re-use and recycle waste. Additionally, the national government further commits itself to adopting regulations to x plastic carrier bags and plastic flat bags. These regulations will urge the plastic industry to produce recyclable plastic bags which will further encourage consumers to recycle and therefore, decrease the entry of plastic into the marine environment. The conclusion in Chapter Five is inferred from Chapter One to Chapter Four of the dissertation. Several shortcomings were observed in the regulatory measures discussed in Chapter Three and Chapter Four, most of which relate to a legal framework weakened by a lack of knowledge on MPP and therefore, an inability to firstly develop measures that expressly deal with the issue, or secondly, develop comprehensive legislative measures that address various types of marine pollution. It is therefore submitted that although South Africa‘s pollution laws in general are exceptional and do address marine pollution, they fail to address MPP sufficiently. As such, Chapter Five presents several policy recommendations in reaction to the findings. , Thesis (LLM) -- Faculty of Law , Public Law, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Vilakazi, Bathobile Thandazile Unittah
- Date: 2021-12
- Subjects: Waste minimization --Law and legislation -- South Africa , Plastic marine debris , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55605 , vital:53364
- Description: Human activities can alter the ordinary operation of Earth-system processes in such a way that it escalates risks in societies across the globe. One of the more visible human activities is the production, consumption and disposal of plastic items and/or materials, the consequences of which are borne by marine life. The dissertation is founded on the premise that conservation of the marine environment must be a priority for all States. States must take responsibility for the prevention of pollution of the marine environment and further take accountability where activities within their territory are causing pollution of the marine environment through the enforcement of legislative measures. The dissertation is drafted in a manner that aims to ultimately deduce whether the current pollution laws in South Africa adequately address marine plastic pollution (MPP). As such, Chapter Two relies on the regulatory position of MPP at the international level. Various legal instruments relating to marine pollution are expounded on such as the LOSC, MARPOL, London Convention and other regional instruments relating particularly to the African continent. The chapter aims to detail the most relevant global instruments that South Africa is a party to and which promote and mandate States parties to protect the marine environment through the implementation and enforcement of regulatory measures. The global measures either exclusively address MPP or provide general provisions for marine environment protection. Chapter Three and Four of the dissertation provide a critical analysis of the legal measures adopted at the national, provincial and local levels respectively to control, reduce and prevent pollution, including MPP. The Constitution of the Republic of South Africa, 1996 requires the national, provincial and local levels of government to co-operate with each other to provide ―effective, efficient, transparent, accountable and coherent governance‖. Therefore, it is essential for this study to investigate the regulation of MPP at all levels of government particularly when the programmes of the national and provincial government must be implemented by local government. The regulatory measures at these levels of government promote the protection of the environment and further prohibit the illegal dumping of waste and littering. They also encourage communities to reduce, re-use and recycle waste. Additionally, the national government further commits itself to adopting regulations to x plastic carrier bags and plastic flat bags. These regulations will urge the plastic industry to produce recyclable plastic bags which will further encourage consumers to recycle and therefore, decrease the entry of plastic into the marine environment. The conclusion in Chapter Five is inferred from Chapter One to Chapter Four of the dissertation. Several shortcomings were observed in the regulatory measures discussed in Chapter Three and Chapter Four, most of which relate to a legal framework weakened by a lack of knowledge on MPP and therefore, an inability to firstly develop measures that expressly deal with the issue, or secondly, develop comprehensive legislative measures that address various types of marine pollution. It is therefore submitted that although South Africa‘s pollution laws in general are exceptional and do address marine pollution, they fail to address MPP sufficiently. As such, Chapter Five presents several policy recommendations in reaction to the findings. , Thesis (LLM) -- Faculty of Law , Public Law, 2021
- Full Text:
- Date Issued: 2021-12
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