title: Design of a Pseudo-Holographic Distributed Time-of-Flight Sonar Range-Imaging System

authors: Streeter, Lee

subjects: Science & Technology

abstract: The design of an audible sonar distributed sensor time-of-flight range imaging system is investigated, sonar being chosen as a substitute for optical range imaging due to cost and simplicity of implementation. The distributed range imaging system proposed is based on the holographic principle where the sensors detect the self interference of the reflected sound from the scene, and the Fourier analysis computes the reflected object profile. An approximate linearised model used in related holographic imaging techniques is found to be inappropriate for the design, and qualitative assessment of simulations show that removing the linearisation dramatically improves image reconstruction. Quantitatively the nonlinear reconstruction improves the RMSE by a factor of 1.3-2.1 times. The full nonlinear reconstruction is slow, and mathematical development lead to 15 fold reduction in computation time.

text: Design of a Pseudo-Holographic Distributed Time-of-Flight Sonar Range-Imaging System The design of an audible sonar distributed sensor time-of-flight range imaging system is investigated, sonar being chosen as a substitute for optical range imaging due to cost and simplicity of implementation. The distributed range imaging system proposed is based on the holographic principle where the sensors detect the self interference of the reflected sound from the scene, and the Fourier analysis computes the reflected object profile. An approximate linearised model used in related holographic imaging techniques is found to be inappropriate for the design, and qualitative assessment of simulations show that removing the linearisation dramatically improves image reconstruction. Quantitatively the nonlinear reconstruction improves the RMSE by a factor of 1.3-2.1 times. The full nonlinear reconstruction is slow, and mathematical development lead to 15 fold reduction in computation time.

year: 2016

title: Enhancing rainfall measurement using microwave links at three scales

authors: Esmaeil Nia, Saeid

abstract: The application of microwave signals in telecommunication has advanced in recent decades. Hence the CMLs (Commercial Microwave Links) have been spread all over the lands. Meanwhile, the decrease in power of the signal due to rainfall has raised the idea of measuring rainfall with microwave attenuation. This PhD research delves into the challenges of these techniques and investigates potential solutions to enhance the accuracy of measuring rainfall. The objectives of the study set to three levels of raindrops’ impact, signal characteristics, and catchment evaluations.  

In the first stage, the cross-sections of different sizes of raindrops are calculated by solving Maxwell’s differential equations in COMSOL software. Rainfall is calculated from different Drop Size Distribution (DSD) models. Then, the correlation between the resulting attenuation and rainfall provided different coefficients for the power correlation between rainfall and attenuation. Regarding the variability in DSD with rainfall intensity, alterations in extinction cross-section play a role in establishing a fluid relationship between attenuation and rainfall. This necessitates adjusting constants for the correlation across different rainfall intensities. 

The results support the idea of having varying coefficients for different rainfall intensities.  At the second level, the signal characteristics were investigated to find a robust method for extracting attenuation from the received power. The study led to defining a reference signal level through signal denoising methods of moving average, Butterworth, and Chebyshev methods. The study showed the superior performance of the moving average in predicting rainfall, especially in 38 GHz links (H and V) indicated by NSE and KGE. Overall, the moving average also resulted in 2%, 16%, and 14% lower RMSE than the conventional method in microwave links 26H, 38H, and 38V, respectively. Butterworth and Chebyshev filters exhibited higher NSE and lower RMSE in 38 GHz links, with competitive accuracy in the 26 GHz link compared to conventional methods.  The effect of wet antenna also decreased and even vanished in some cases. 

At last, the catchment runoff was used to calibrate the relationship between rainfall and attenuation. In a study in 15 catchments in Melbourne, the suggested method established a relation between attenuation and the quick flow of 15 flow stations. Meanwhile, the coefficients of the rainfall-attenuation formula were calibrated to reach the highest accuracy of runoff prediction. The results indicate a more robust connection between attenuation and quick flow in contrast to conventional rain gauge data. The new suggested method achieved a maximum NSE of 0.78 and KGE of 0.86. Compared to rain gauges, the conventional CML model improved NSE by an average of 197%, while the new model showed an additional 50% enhancement. RMSE optimisation also demonstrated improvement, with a 15% enhancement using the conventional CML model and an additional 4% on average with the new model. Moreover, the revised flow calibration technique reduces the wet antenna effect by an average of 49%.

text: Enhancing rainfall measurement using microwave links at three scales The application of microwave signals in telecommunication has advanced in recent decades. Hence the CMLs (Commercial Microwave Links) have been spread all over the lands. Meanwhile, the decrease in power of the signal due to rainfall has raised the idea of measuring rainfall with microwave attenuation. This PhD research delves into the challenges of these techniques and investigates potential solutions to enhance the accuracy of measuring rainfall. The objectives of the study set to three levels of raindrops’ impact, signal characteristics, and catchment evaluations.  

In the first stage, the cross-sections of different sizes of raindrops are calculated by solving Maxwell’s differential equations in COMSOL software. Rainfall is calculated from different Drop Size Distribution (DSD) models. Then, the correlation between the resulting attenuation and rainfall provided different coefficients for the power correlation between rainfall and attenuation. Regarding the variability in DSD with rainfall intensity, alterations in extinction cross-section play a role in establishing a fluid relationship between attenuation and rainfall. This necessitates adjusting constants for the correlation across different rainfall intensities. 

The results support the idea of having varying coefficients for different rainfall intensities.  At the second level, the signal characteristics were investigated to find a robust method for extracting attenuation from the received power. The study led to defining a reference signal level through signal denoising methods of moving average, Butterworth, and Chebyshev methods. The study showed the superior performance of the moving average in predicting rainfall, especially in 38 GHz links (H and V) indicated by NSE and KGE. Overall, the moving average also resulted in 2%, 16%, and 14% lower RMSE than the conventional method in microwave links 26H, 38H, and 38V, respectively. Butterworth and Chebyshev filters exhibited higher NSE and lower RMSE in 38 GHz links, with competitive accuracy in the 26 GHz link compared to conventional methods.  The effect of wet antenna also decreased and even vanished in some cases. 

At last, the catchment runoff was used to calibrate the relationship between rainfall and attenuation. In a study in 15 catchments in Melbourne, the suggested method established a relation between attenuation and the quick flow of 15 flow stations. Meanwhile, the coefficients of the rainfall-attenuation formula were calibrated to reach the highest accuracy of runoff prediction. The results indicate a more robust connection between attenuation and quick flow in contrast to conventional rain gauge data. The new suggested method achieved a maximum NSE of 0.78 and KGE of 0.86. Compared to rain gauges, the conventional CML model improved NSE by an average of 197%, while the new model showed an additional 50% enhancement. RMSE optimisation also demonstrated improvement, with a 15% enhancement using the conventional CML model and an additional 4% on average with the new model. Moreover, the revised flow calibration technique reduces the wet antenna effect by an average of 49%.

year: 2024

title: Grounding the state of exception in New Zealand: A case study of racial segregation in Pukekohe, Whiteness and the Carceral State

authors: Martin, Jessica

subjects: State of exception

abstract: Indigenous scholars in settler-colonial contexts have highlighted the hyper-imprisonment of Indigenous people, locating it as an extension of the colonial project. Although research on this issue in New Zealand is emerging, there is a notable gap in understanding how the carceral state has developed within this particular context. This study aims to address the following research question: How does the historical context of racial segregation in Pukekohe contribute to our understanding of the mechanisms of the carceral state in New Zealand?
To thoroughly examine the hyper-imprisonment of Māori, it is essential to unpack the historical origins of state violence. Despite existing research establishing a link between Māori over-representation in prisons and the enduring effects of colonisation, there is a lack of studies exploring the complex interplay among the carceral state, whiteness, policy, policing, and law, which collectively shape the current landscape of incarceration. This study focuses on the racial segregation in Pukekohe between 1920 and 1960 and utilises reflexive thematic analysis within a case study framework, drawing on the insights offered by Robert Bartholomew's book, No Māori Allowed (2020). The analysis centres on the theoretical concept of the state of exception, shedding light on how power was wielded by the white racial polity. Thus, providing a unique perspective on the carceral state and state-sanctioned violence.
The findings highlight the interconnectedness of various systemic control mechanisms employed by the carceral state. Housing, policing, and whiteness emerge as crucial factors in the control and confinement of Māori in Pukekohe. By emphasising the role of whiteness in suppressing this history, this study underscores the need for critical examination and recognition of white cultural imperialism as a fundamental pillar of the carceral state. Overall, this research offers significant insights into the construction of a targeted population and the enduring consequences of state-sanctioned violence, emphasising the importance of a comprehensive examination of New Zealand's racialised history in discussions on the hyper-imprisonment of Māori.

text: Grounding the state of exception in New Zealand: A case study of racial segregation in Pukekohe, Whiteness and the Carceral State Indigenous scholars in settler-colonial contexts have highlighted the hyper-imprisonment of Indigenous people, locating it as an extension of the colonial project. Although research on this issue in New Zealand is emerging, there is a notable gap in understanding how the carceral state has developed within this particular context. This study aims to address the following research question: How does the historical context of racial segregation in Pukekohe contribute to our understanding of the mechanisms of the carceral state in New Zealand?
To thoroughly examine the hyper-imprisonment of Māori, it is essential to unpack the historical origins of state violence. Despite existing research establishing a link between Māori over-representation in prisons and the enduring effects of colonisation, there is a lack of studies exploring the complex interplay among the carceral state, whiteness, policy, policing, and law, which collectively shape the current landscape of incarceration. This study focuses on the racial segregation in Pukekohe between 1920 and 1960 and utilises reflexive thematic analysis within a case study framework, drawing on the insights offered by Robert Bartholomew's book, No Māori Allowed (2020). The analysis centres on the theoretical concept of the state of exception, shedding light on how power was wielded by the white racial polity. Thus, providing a unique perspective on the carceral state and state-sanctioned violence.
The findings highlight the interconnectedness of various systemic control mechanisms employed by the carceral state. Housing, policing, and whiteness emerge as crucial factors in the control and confinement of Māori in Pukekohe. By emphasising the role of whiteness in suppressing this history, this study underscores the need for critical examination and recognition of white cultural imperialism as a fundamental pillar of the carceral state. Overall, this research offers significant insights into the construction of a targeted population and the enduring consequences of state-sanctioned violence, emphasising the importance of a comprehensive examination of New Zealand's racialised history in discussions on the hyper-imprisonment of Māori.

year: 2024