Estimation of tropospheric wet delay from GNSS measurements

The determination of the zenith wet delay (ZWD) component can be a difficult task due to the dynamic nature of atmospheric water vapour. However, precise estimation of the ZWD is essential for high-precision Global Navigation Satellite System (GNSS) applications such as real-time positioning and Numerical Weather Prediction (NWP) modelling.The functional and stochastic models that can be used for the estimation of the tropospheric parameters from GNSS measurements are presented and discussed in this study. The focus is to determine the ZWD in an efficient manner in static mode. In GNSS, the estimation of the ZWD is directly impacted by the choice of stochastic model used in the estimation process. In this thesis, the rigorous Minimum Norm Quadratic Unbiased Estimation (MINQUE) method was investigated and compared with traditional models such as the equal-weighting model (EWM) and the elevationangle dependent model (EADM). A variation of the MINQUE method was also introduced. A simulation study of these models resulted in MINQUE outperforming the other stochastic models by at least 36% in resolving the height component. However, this superiority did not lead to better ZWD estimates. In fact, the EADM provided the most accurate set of ZWD estimates among all the models tested. The EADM also yielded the best ZWD estimates in the real data analyses for two independent baselines in Australia and in Europe, respectively.The study also assessed the validity of a baseline approach, with a reduced processing window size, to provide good ZWD estimates at Continuously Operating Reference Stations (CORS) in an efficient manner. Results show that if the a-priori station coordinates are accurately known, the baseline approach, along with a 2-hour processing window, can produce ZWD estimates that are statistically in good agreement with the estimates from external sources such as the radiosonde (RS), water vapour radiometer (WVR) and International GNSS Service (IGS) solutions. Resolving the ZWD from GNSS measurements in such a timely manner can aid NWP model in providing near real-time weather forecasts in the data assimilation process.In the real-time kinematic modelling of GNSS measurements, the first-order Gauss- Markov (GM) autocorrelation model is commonly used for the dynamic model in Kalman filtering. However, for the purpose of ZWD estimation, it was found that the GM model consistently underestimates the temporal correlations that exist among the ZWD measurements. Therefore, a new autocorrelation dynamic model is proposed in a form similar to that of a hyperbolic function. The proposed model initially requires a small number of autocorrelation estimates using the standard autocorrelation formulations. With these autocorrelation estimates, the least-squares method is then implemented to solve for the model’s parameter coefficients. Once solved, the model is then fully defined. The proposed model was shown to be able to follow the autocorrelation trend better than the GM model. Additionally, analysis of real data at an Australian IGS station has showed the proposed model performed better than the random-walk model, and just as well as the GM model. The proposed model was able to provide near real-time (i.e. 30 seconds interval) ZTD estimates to within 2 cm accuracy on average.The thesis also included an investigation into the several interpolation models for estimating missing ZWD observations that may take place during temporary breakdowns of GNSS stations, or malfunctions of RS and WVR equipments. Results indicated marginal differences between the polynomial regression models, linear interpolation, fast-Fourier transform and simple Kriging methods. However, the linear interpolation method, which is dependent on the two most recent data points, is preferable due to its simplicity. This result corresponded well with the autocorrelation analysis of the ZWD estimates where significant temporal correlations were observed for at most two hours.The study concluded with an evaluation of several trend and smoothing models to determine the best models for predicting ZWD estimates, which can help improve real-time kinematic (RTK) positioning by mitigating the tropospheric effect. The moving average (MA) and the single-exponential smoothing (SES) models were shown to be the best-performing prediction models overall. These two models were able to provide ZWD estimates with forecast errors of less 10% for up to 4 hours of prediction

Interpolation of the GNSS Wet Troposphere Delay

Troposphere delay is one of the main distance-dependent errors in Global Navigation Satellite Systems (GNSS) observations. Precise estimation of the troposphere wet delay is necessary to aid ambiguity resolution and for positioning in network Real-Time Kinematic (RTK) and Precise Point Positioning. Wet tropospheric estimates can also serve as a source of atmospheric information to facilitate weather forecasting. Interpolation of the troposphere wet delay is thus required when its estimation is interrupted for short periods or when data are processed at higher intervals from that of available data. The objective of this research is to compare the performance of several interpolation methods that can be used in order to suggest the most appropriate technique. Six interpolation models were considered. The models ranged from the easy-to-implement linear model, to the more sophisticated Kriging model. Other models considered are the cubic spline interpolation, cubic Hermite polynomial interpolation, Lagrange polynomial interpolation, and Fast Fourier transform interpolation. The performance of these methods was assessed by comparing their results with actual troposphere wet delay data collected at the station Onsala (ONSA) in Sweden. As the number of observations used to generate the interpolation process affects the determination of the model coefficients; the use of different lengths of observations was investigated. The number of missing wet delay values considered for interpolation during testing ranged from one to four in a row.Test results showed that the linear interpolation, the cubic Hermite polynomial and fast Fourier transform models produce better estimates than splines and ordinary Kriging. The Lagrange polynomials method was the poorest performer. The paper provides explanation of the interpolation results achieved by linking them with autocorrelation of the troposphere wet delays

Dynamic Modelling of Zenith Wet Delay in GNSS Measurements

Proper modelling of the temporal correlations of the zenith wet delay (ZWD) is important in some of the Global Navigation Satellite Systems (GNSS) applications such as estimation of the Perceptible Water Vapour (PWV), and methods such as Precise Point Positioning (PPP). The random walk (RW) and the first-order Gauss- Markov (GM) autocorrelation model are commonly used for the dynamic modelling of ZWD in Kalman filtering of GNSS measurements. However, it was found that the GM model consistently underestimates the temporal correlations that exist among the ZWD estimates. Therefore, a new autocorrelation dynamic model is proposed in a form similar to that of a hyperbolic function. The impact of the proposed dynamic model on the near-real time estimation of the ZWD was tested and its results were compared to that of the GM model as well as the RW model. In this test, GPS dual-frequency data collected on the 25th Jan 2010 at two Western Australian IGS stations, namely, Yarragadee and Karratha, were used. Results showed that the proposed model outperformed the GM model, and when added to hydrostatic models were able to provide near real-time (with 30 seconds intervals) ZTD estimates to within a few cm accuracy

Work-integrated learning builds student identification of employability skills: Utilizing a food literacy education strategy

© 2020 International Journal of Work-Integrated Learning. All rights reserved. Enterprising students who understand the work environment are considered more employable. It is accepted that higher-education has a responsibility to produce career-ready-graduates. Practicum experience provides a critical role in this preparation. This study describes the development and implementation of the WIL instrument and WIL experience to assess the perceived skill development of students (n=19). This research utilized three data capture points; 1) employability skills cluster matrix-self-assessment tool (ESCM-SAT), 2) industry feedback from supervisors to develop a deeper understanding of the value of WIL; 3) students used the Gibbs reflective cycle (Gibbs 1988). There were improvements in all skills clusters, main gains were in career management (p \u3c 0.01). Supervisor feedback gave direction for improvement for; communication, preparation and organization skills. Student reflection suggests career management skills were strengthened, confidence increased, as did their value of academics. The ESCM-SAT, industry feedback and student reflection were deemed a suitable combination to measure the WIL experiences from a student perspective

Impact of stochastic modelling on GPS height and zenith wet delay estimation

Most stochastic modelling techniques assume the physical correlations among the raw observations to be negligible when forming the variance covariance matrix of the GPS observations. Such an assumption may, however, lead to significantly biased solutions. The Minimum Norm Quadratic Unbiased Estimation (MINQUE) method is an iterative technique that can be used to estimate spatial correlation among GPS measurements. Studies by previous authors have shown that MINQUE improves the accuracy and the reliability of the ambiguity resolution, and ultimately, the geodetic solution. However, its effect on the estimation of zenith wet delay (ZWD) is somewhat unknown. In this paper, an investigation into its impact on ZWD, as well as heighting, is carried out using simulated data. The results obtained from MINQUE for an observation window of five-days in static mode indicate an average improvement of 51% and 71% in the station height precision when compared against elevation-angle dependent and equal weighting models, respectively. This development, however, did not translate into better ZWD estimation, for which the differences between each respective stochastic model are generally at the sub-millimetre level

Assessing the efficacy of TNF-alpha inhibitors in preventing emergency and emergent colectomies

Background and Aim: Severe ulcerative colitis (UC) is potentially life threatening and is associated with significant morbidity. TNF-∝ inhibitors (Infliximab) were introduced in Australia for the management of medically resistant, acute, severe flares of UC in 2008. The aim of this study is to assess the efficacy of Infliximab in preventing emergent and emergency colectomies for patients with moderate to severe UC by comparing colectomy rates before and after its introduction at our institution. Methods: This was a retrospective cohort study of all patients who were admitted to the Royal Perth Hospital with a flare of UC between 2002 and 2017. Patients were divided into two cohorts: those admitted prior to the introduction of Infliximab (pre-2008) and those admitted after. We compared data between these two groups, including age, gender, length of admission, use of Infliximab, colectomy, and complications of surgery. We defined emergency surgery as requiring surgery during the index admission and emergent surgery as an operation within 54 weeks. Results: A total of 313 UC cases from 2002 to 2017 were analyzed. There was a decrease in emergency and emergent colectomies from 19.4 to 8% in the post-2008 cohort (P = 0.008). Furthermore, there was a decrease in the proportion of operations performed as emergencies, from 36 to 20%. This resulted in a significantly reduced length of stay (13.4–9.7 days, P \u3c 0.05) and complication rate (36 to 20%, P \u3c 0.05). Conclusion: Overall, the need for emergency and emergent operations has drastically reduced at our institution with the introduction of Infliximab. This study has confirmed the efficacy of Infliximab in reducing colectomy rates at our institution. © 2019 The Authors. JGH Open: An open access journal of gastroenterology and hepatology published by Journal of Gastroenterology and Hepatology Foundation and John Wiley & Sons Australia, Ltd

Compliance, palatability and feasibility of paleolithic and Australian guide to healthy eastin diets in healtthy women: A 4-week dietary intervention

The Paleolithic diet has been receiving media coverage in Australia and claims to improve overall health. The diet removes grains and dairy, whilst encouraging consumption of fruits, vegetables, meat, eggs and nuts. Our aim was to compare the diet to the Australian Guide to Healthy Eating (AGHE) in terms of compliance, palatability and feasibility; (2) Subjects/Methods: 39 healthy women (age 47 ± 13 years, BMI 27 ± 4 kg/m2) were randomised to an ad-libitum Paleolithic (n = 22) or AGHE diet (n = 17) for 4-weeks. A food checklist was completed daily, with mean discretionary consumption (serves/day) calculated to assess compliance. A 12-item questionnaire was administered post intervention to assess palatability and feasibility; (3) Results: The AGHE group reported greater daily consumption of discretionary items (1.0 + 0.6 vs. 0.57 + 0.6 serves/day, p = 0.03). Compared to the AGHE group, the Paleolithic group reported a significantly greater number of events of diarrhoea (23%, 0%, p = 0.046), costs associated with grocery shopping (69%, 6% p \u3c 0.01) and belief that the diet was not healthy (43%, 0% p \u3c 0.01); (4) Conclusions: Compliance to both diets was high but the potential side effects and increased cost suggest that the Paleolithic diet may not be practical in clinical/public health settings. Further studies are required to assess longer term feasibilit

A framework for cryptography algorithms on mobile devices

Mobile communication devices have become a popular tool for gathering and disseminating information and data. With the evidence of the growth of wireless technology and a need for more flexible, customizable and better-optimised security schemes, it is evident that connection-based security such as HTTPS may not be sufficient. In order to provide sufficient security at the application layer, developers need access to a cryptography package. Such packages are available as third party mobile cryptographic toolkits or are supported natively on the mobile device. Typically mobile cryptographic packages have reduced their number of API methods to keep the package lightweight in size, but consequently making it quite complex to use. As a result developers could easily misuse a method which can weaken the entire security of a system without knowing it. Aside from the complexities in the API, mobile cryptography packages often do not apply sound cryptography within the implementation of the algorithms thus causing vulnerabilities in its utilization and initialization. Although FIPS 140-2 and CAPI suggest guidelines on how cryptographic algorithms should be implemented, they do not define the guidelines for implementing and using cryptography in a mobile environment. In our study, we do not define new cryptographic algorithms, instead, we investigate how sound cryptography can be applied practically in a mobile application environment and developed a framework called Linca (which stands for Logical Integration of Cryptographic Architectures) that can be used as a mobile cryptographic package to demonstrate our findings. The benefit that Linca has is that it hides the complexity of making incorrect cryptographic algorithm decisions, cryptographic algorithm initialization and utilization and key management, while maintaining a small size. Linca also applies sound cryptographic fundamentals internally within the framework, which radiates these benefits outwards at the API. Because Linca is a framework, certain architecture and design patterns are applied internally so that the cryptographic mechanisms and algorithms can be easily maintained. Linca showed better results when evaluated against two mobile cryptography API packages namely Bouncy Castle API and Secure and Trust Service API in terms of security and design. We demonstrate the applicability of Linca on using two realistic examples that cover securing network channels and on-device data.Dissertation (MSc (Computer Science))--University of Pretoria, 2007.Computer ScienceMScunrestricte

Increasing food expenditure in long daycare by an extra $0.50 per child/day would improve core food group provision

Early childhood education and care services are a significant feature of Australian family life, where nearly 1.4 million children attended a service in 2019. This paper reports on the cost of food provided to children in long day-care (LDC) services and extrapolates expenditure recommendations to support food provision compliance. A cross-sectional audit of LDC services in metropolitan Perth was conducted to determine food group provision by weighing raw ingredients of meal preparation—morning tea, lunch, and afternoon tea (MT, L, AT). Ingredients were costed at 2017 online metropolitan pricing from a large supermarket chain. Across participating services, 2 days of food expenditure per child/day ranged between $1.17 and$4.03 across MT, L, AT, and averaged $2.00 per child/day. Multivariable analysis suggests that an increase of$0.50 per child/day increases the odds of a LDC service meeting \u3e 50% of Australian Dietary Guideline (ADG) recommendations across ≥ 4 core food groups by fourfold (p = 0.03). Given the fact that the literature regarding food expenditure at LDC services is limited, this study provides information about food expenditure variation that impacts planning and provision of nutritionally balanced menus recommended for children. An average increase of food expenditure of $0.50 per child/day would increase food provision compliance

Can we predict expected adenoma weight preoperatively with reference to the correlation of preoperative biochemical tests with parathyroid adenoma weight?

Background: Primary hyperparathyroidism is a prevalent disease with proven benefits for appropriately selected patients who undergo parathyroidectomy. The ability to accurately predict expected single adenoma gland weight as the cause based on preoperative biochemical tests could improve cure rates in a minimally invasive approach. Objective: To assess the correlation between parathyroid weight and preoperative parathyroid hormone and calcium levels in patients with primary hyperparathyroidism with a solitary adenoma and determine if these could be used to predict expected parathyroid weight. Methods: Patients with primary hyperparathyroidism who underwent curative parathyroidectomy from 2013 to 2018 was retrospectively analysed. Results: There is a strong positive correlation r = 0.602 between preoperative PTH levels with respect to parathyroid weight (p \u3c 0.001). There was a moderate correlation r = 0.474 between preoperative adjusted Calcium and PTH weight (p \u3c 0.001). An algorithm was developed to calculate predicted weight of a single adenoma but when tested against cases with hyperplasia and double adenomas during the period, the variability of predicted weight meant it was impossible to differentiate between the causes. Hyperplasia was excluded and 95% of double adenomas excluded however, when parathyroid weight exceeded 1200 mg. Conclusion: There is a strong correlation between preoperative PTH levels and calcium levels with parathyroid weight. The large variability of predicted parathyroid weight however, precludes the use of biochemical tests alone preoperatively in being able to differentiate between a single adenoma, double adenoma or hyperplasia as the cause in primary hyperparathyroidism. At parathyroid predicted weights above 1200 mg however, all cases of hyperplasia, and 95% of double adenomas excluded