Browsing by Author "Santos, Marcelo"

Now showing 1 - 11 of 11
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    A comparison of geopotential models using GPS observations on first order orthometric benchmarks
    (University of New Brunswick, 2006) Lunn, Johnathan; Santos, Marcelo
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    Accuracy of the classical height system
    (University of New Brunswick, 2018) Foroughi, Ismael; Santos, Marcelo; Vaníček, Petr
    Measuring the quality of the classical height system through its self-consistency (congruency) is investigated in this dissertation. Measuring the congruency is done by comparing the geoidal heights determined from a gravimetric geoid model with test geoidal heights derived at GNSS/Leveling points. The components of this measurement are computed as accurately as possible, e.g., the Stokes-Helmert approach is used to determine the geoid model, gravimetric and topographic corrections are applied to the spirit leveling observations to derive rigorous orthometric heights at test points, and finally, the geodetic heights are taken from GNSS observations. Four articles are included in this dissertation, one is discussing a modification to the Stokes-Helmert approach for using the optimal contribution of the Earth gravitational models and the local data. The second paper applies the methodology presented in the first paper and presents the detail results for a test area. The third paper is a discussion on the accuracy of the classical height system against Molodensky’s system and presents a numerical study to show that the classical system can be computed as accurately as Molodensky’s. The last paper presents a methodology to find the most probable solution of the downward continuation of surface gravity to the geoid level using the least-squares technique. The uncertainties of the geoidal heights are estimated using least-square downward continuation and a priori variance matrix of the input gravity data. The total estimation of the uncertainties of the geoidal heights confirms that geoid can be determined with sub-centimetre accuracy in the flat areas when, mainly, the effect of topographic mass density is taken into account properly, the most probable solution of downward continuation is used, and the improved satellite-only global gravitational models are merged with local data optimally.
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    Atmospheric delay modelling for ground-based GNSS reflectometry
    (University of New Brunswick, 2020) Nikolaidou, Thalia; Santos, Marcelo; Geremia-Nievinski, Felipe
    Several studies have demonstrated the utility of global navigation satellite system reflectometry (GNSS-R) for ground-based coastal sea-level altimetry. Recent studies evidenced the presence of atmospheric delays in GNSS-R sea-level retrievals and by-products such as tidal amplitudes. On the one hand, several ad-hoc atmospheric correction formulas have been proposed in the literature. On the other hand, ray-tracing studies applied for GNSS-R show little information about the methods and algorithms involved. This dissertation is based on three articles which establish the theoretical framework of the atmospheric delay experienced in ground-based GNSS-R altimetry. In the first article, we defined the atmospheric interferometric delay in terms of the direct and reflected atmospheric delays as well as the vacuum distance and radio length. Then, we clarified the roles of linear and angular refraction, derived the respective delays and combined them in the total delay. We also introduced for the first time two subcomponents of the atmospheric geometric delay, the geometric-shift and the geometric-excess, unique for reflected signals. The atmospheric altimetry correction necessary for unbiased sea-level retrievals was defined as half the rate-of-change of the atmospheric delay with respect to the sine of satellite elevation angle. We developed a ray-tracing procedure to solve rigorously the three-point boundary value problem involving transmitting satellite, reflecting surface, and receiving antenna. We hence evaluated the atmospheric bias in sea-level retrievals for a range of typical scenarios, showing its dependence on elevation angle and reflector height. In the second article, we demonstrated that rigorous ray-tracing of the bent ray can be simplified by a judicious choice of rectilinear wave propagation model. This facilitates the adaptation by existing GNSS ray-tracing procedures, besides numerical and speed advantages. Further it was emphasized that mapping functions developed for GNSS positioning cannot be reused for GNSS-R purposes without adaptations. In the third article, we developed closed-form expressions of the atmospheric delay and altimetry correction for end-users without access or expertise in ray-tracing. These expressions rely only on direct elevation bending and mean refractivity at the site. Finally, we determined cut-off elevation angle and reflector height, for neglecting atmospheric delays. These limiting conditions are useful in observation planning and error budgeting of the GNSS-R altimetry retrievals.
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    Demarcation and registration of indigenous land in Brazil
    Hutchison, Meredith; Nichols, Sue; Santos, Marcelo; Onsrud, Hazel; Paixao, Silvane
    11 years after the demarcation deadline mandated by Brazil’s 1988 promulgated constitution, over 45% of indigenous territories have still not been demarcated. To explore how the demarcation process continues to be physically obstructed the current framework under which indigenous territories are demarcated and registered, and the conflicting interests that impede this process will be explored. Later, to illustrate the magnitude of this problem, a historical overview of the government’s prioritisation of indigenous issues will also be examined. In sum, this report will explore why Brazil’s demarcation delay has persisted, despite the fact that indigenous people desperately require secure land tenure to protect their unique lifestyles.
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    Demarcation and registration of indigenous land in Brazil
    Hutchison, Meredith; Nichols, Sue; Santos, Marcelo; Onsrud, Hazel; Paixao, Silvane
    11 years after the demarcation deadline mandated by Brazil’s 1988 promulgated constitution, over 45% of indigenous territories have still not been demarcated. To explore how the demarcation process continues to be physically obstructed the current framework under which indigenous territories are demarcated and registered, and the conflicting interests that impede this process will be explored. Later, to illustrate the magnitude of this problem, a historical overview of the government’s prioritisation of indigenous issues will also be examined. In sum, this report will explore why Brazil’s demarcation delay has persisted, despite the fact that indigenous people desperately require secure land tenure to protect their unique lifestyles.
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    Evaluation of precise point positioning derived zenith total delays from the Nigerian GNSS reference network
    (University of New Brunswick, 2019) Mayaki, Anthony Omeiza; Santos, Marcelo
    The Zenith Total Delay (ZTD) from ground-based Global Navigational Satellite System (GNSS) observations is a valuable information source for studying the Earth’s troposphere. Since almost all weather is formed in the troposphere, an analysis of a collection of ZTD time series can provide insight about the behavior of the weather of a place. Several institutions around the world involved in meteorological operations assimilate the ZTD from networks of GNSS continuously operating reference stations (CORS) into Numerical Weather Models (NMW) for better weather forecasting. In Nigeria however, there are no operational GNSS networks used for meteorological purposes. The focus of this thesis is to determine the suitability of the Nigerian GNSS Reference Network (NIGNET) stations for meteorological applications by evaluating the ZTDs obtained from it through precise point positioning (PPP). PPP derived ZTDs from surrounding International GNSS Service (IGS) stations are also included for comparison. These PPP derived ZTDs, spanning from 2011 to 2016, are compared with ZTDs computed from the National Centre for Environmental Prediction reanalysis II (NCEP II) global NWM and from the IGS. A comprehensive time series analysis (least-squares spectral analysis) is performed to determine the spatio-temporal variations of the ZTDs of stations across Nigeria and to evaluate the level of agreement between the three (3) ZTD sources. The comparisons generally show good agreement between the 3 sources with the mean differences lower than 24.2 mm and root mean square errors lower than 45.8 mm. The spectral analyses reveal the various periodic oscillations in the ZTD and how they are influenced by pressure and temperature through the component hydrostatic and wet delays of the ZTD. This research contributes to the characterization of the nature of the troposphere over Nigeria and affirms the relevance of the NIGNET as a tool for meteorology in Nigeria.
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    Implementation and validation of a UNB Vienna Mapping Functions service
    (University of New Brunswick, 2013) McAdam, Matthew; Santos, Marcelo
    The mitigation of space borne radio signal perturbations in the neutral atmosphere is necessary for high precision position applications. Over the years there have been many methods for dealing with these perturbations, but the most popular modern method to deal with such effects is to model the signal delay at zenith with a corresponding mapping function that describes the elevation angle dependancy of the signal. There have been many formulations and realizations of mapping functions, but the Vienna Mapping Functions (VMF) have proven to be most accurate to date. The Vienna Mapping Functions (VMF) are unique in that they rely solely on information from an external data source, namely a numerical weather prediction model (NWP). The development of the VMF represents a shifting paradigm in which geodetic corrections are moving from simple mathematical closed form type solutions to solutions based on large amounts of external data. However, there have been many differing institutions creating many differing corrections based on many differing underlying models and datasets. The intent of this work is to investigate the influence of differing external datasets and modelling algorithms with a new realization of the VMF1. This is accomplished with the creation of a UNB Vienna Mapping Functions Service (VMF1) where several VMF1 products have been created with an independent data source (NCEP and CMC) and independent ray-tracing algorithms (UNB Ray tracer). The new service will not only improve the redundancy of currently available corrections, stimulate the use of the VMF1 corrections and add to the creation of a consistent set of corrections based on the same underlying external datasets, but the new service will help to appreciate the influence of the application of these external datasets. The resulting UNB-VMF1 service has been validated against the existing service operated at TU Vienna. Three realizations have been created: (a) an NCEP based product, (b) CMC (GDPS) based product, and a (c) forecast products based on 24-42h hour forecast from the CMC. The validation of the NCEP based product has been conducted over an 11-year period and the remaining products have been evaluated over an 8-month period. All products have been evaluated in the gridded domain and the position domain with the comparison of PPP solutions. With respect to the existing VMF1 service, all products are considered equivalent at the 1σ level, but the NCEP based product exceeds the accuracy of the VMF1 at the 3σ level. In particular, the NCEP based product performs poorly in regions of steep topography due to limitations of the model’s integration of the underlying orography. In addition to the validation of the service, the NCEP and CMC numerical weather prediction models (NWP), and an empirical model known as the GPT, have been assessed against measured in-situ meteorological measurements (pressure, temperature and humidity) and hydrostatic zenith delays computed by in-situ measurements. The NCEP dataset performed the worst out of the selected NWPs and the GPT performed worse in general. The GPT and NCEP exhibited a latitude dependent bias in the RMS of the difference in pressure and hydrostatic zenith delay. The CMC results did not exhibit any noticeable latitude dependancy for these parameters. Each dataset exhibited a seasonal trend where the RMS of the difference is larger during the winter months for the pressure parameter. Both the CMC and NCEP models exhibited a trend where the RMS of the difference in humidity correlated with the season and latitude. In regions and times of the year when water vapour content is largest, both NWPs experienced a degradation in their ability to model the humidity parameter.
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    Improvements to satellite global gravity field modelling
    (University of New Brunswick, 2019) Sheng, Michael Baier; Santos, Marcelo; Vaníček, Petr
    Modelling the gravity field of the Earth is important for many scientific disciplines. Global gravity models allow for the investigation of long-wavelength properties of the gravity field. Global models derived from satellite observations provide an additional benefit: they are uncorrelated with any error contaminating regional terrestrial gravity information; this makes them ideal for combination with terrestrial gravity data in order to formulate high-precision regional geoid models. This dissertation investigates several possible areas of improvement to both the formulation and evaluation of satellite-only global gravity models. The first major barrier is due to what is known to the geodetic community as the “polar-gap problem”: the lack of data collected by the satellites over the poles due to the inclination angle of their orbit. The second is the rigorous application of these models inside of the topographical masses (and most pertinent, on the surface of the geoid). These problems are addressed in three articles. The first presents a mathematical tool that can be used in order to address the polar-gap problem by performing the global integration making use of the additivity property of Riemann integrals. The second article presents a computational scheme that allows for the evaluation of various quantities derived from global gravity models inside the topographical masses. Finally, the third article describes the production and validation of a 2D global topographical density model that is required for the rigorous evaluation of the gravity field as prescribed in the second article.
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    Measurement-based geospatial data management
    (University of New Brunswick, 2019) Bremner, Michael; Santos, Marcelo
    Most land surveying firms use ad hoc data management systems that inhibit the reuse of existing data and make it difficult to identify redundant work. This causes systematic inefficiencies in land survey operations. This project aims to provide a solution to this inefficiency by researching data management methods for land survey data. Measurement-Based GIS (MBGIS) is selected as the avenue for this research because of previous literature discussing the potential benefits of its use as a land survey data management system. Unfortunately, existing implementations have issues with processing times and flexibility of data integration. Further research requires a MBGIS prototype to be implemented. A conceptual design of a full data management system is created to provide context for the design and implementation of the prototype. The prototype is developed as a geodetic library and a suite of data integration tests. Each of the tests integrates a series of discrete datasets into a network using a different data integration strategy. The processing times, precision of the resulting networks, and flexibility of the strategies are compared. Two of the strategies provide very similar, positive results. It appears that a MBGIS performing rigorous geodetic reductions of measurements and using one of the two successful integration strategies could be used as a data management system and could improve the efficiency of land survey operations.
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    Simulation and prototyping of integration methods between GNSS, INS, and signals-of-opportunity sources
    (University of New Brunswick, 2020) Mendonça, Marco; Santos, Marcelo
    Seamless positioning and navigation are a recurring academic and industrial challenge due to single sensor solutions' limitations. Modern technologies allow developers to work with multiple sensors and signals in parallel, solving systems of equations that a decade ago would not be handled in real-time. In this context, this research aims to explore the plausible integration between absolute GNSS positioning, inertial systems, and two signal-of-opportunity candidates: Wi-Fi and 5G mmWave signals. The integration of different signals and sensors is explored in a low computational power filter context, such as the extended Kalman filter (EKF), particle filter (PF), and one of the most efficient machine learning algorithms: the support vector machine (SVM). All three methods have been used for a long time in the most different applications. In this thesis, their loosely and tightly integration will be explored to design, implement, and develop novel positioning algorithms using the strengths of different sensors and filters. Currently, literature is not settled on this integration's potential, therefore, creating a need for more comprehensive developments and tests in this scope. Furthermore, this thesis presents a framework for simulation and validation of sensor integration algorithms and novel contributions for multi-sensor navigation, including integration at the post-filter constraint level and machine-learning aided filtering. The methods proposed in this thesis were implemented with real-time application considerations and shown to be beneficial in challenging urban areas scenarios. Improvements in accuracy ranging from 90.1% in horizontal accuracy compared to the GNSS-only solution and 36.4% when compared to GNSS and Inertial System (INS) solution are achieved in real-world data. Integrity metrics are also shown to be improved between 1 and 14% when utilizing signal-of-opportunity information. With simulated mmWave ranging methods, the GNSS solution is shown to be significantly more robust, improving accuracy by up to 69.4% in the horizontal axis and an improved error and uncertainty estimation with values up to 12% better. The results and analysis are presented considering the scientific and industrial standards, leading to the conclusion that cost-effective methods built with off-the-shelf equipment can improve the current standard in sensor integration for navigation.
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    The gravimetric geoid for Mexico: xGGM23
    (University of New Brunswick, 2024-03) Avalos-Naranjo, David; Santos, Marcelo
    The work presented in this thesis deals with the construction of a new gravimetric geoid model for Mexico. A large amount of terrestrial gravimetry collected up to year 2020 was processed in spectral combination with the satellite-derived geopotential model GOCO06s using the UNB’s Stokes-Helmert technique. The geoid model complies with international standards of the regional geoid for North and Central America and its resolution of 2.5 arc minutes is coherent with the actual spacing in gravimetry data holdings for the country. It was found that the new geoid model agrees with the national vertical datum by 10 cm in standard deviation, which implies a significant improvement from previous models. Improvements are mainly due to the recent densification of terrestrial gravity surveys, refinements in the software code of the SHGeo package, and an optimization process to select the frequency on which the terrestrial input data takes over from the satellite source.