Monitoramento e avaliação de processos erosivos marginais em reservatórios de usinas hidrelétricas por meio de varredura a laser

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Integridade no posicionamento RTK e RTK em rede

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Integridade, disponibilidade e acurácia no posicionamento RTK e RTK em rede: Investigação no contexto da rede GNSS ativa do Estado de São Paulo

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

GPS/VRS positioning using atmospheric modeling

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Monitoramento das irregularidades ionosféricas e cintilação dos sinais GNSS: em tempo real e pós-processado

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Metodologia para avaliação do desempenho de receptor de GPS de uso agrícola em condição cinemática

Activities that use Global Navigation Satellite System (GNSS) are countless and the most used one is the Global Positioning System (GPS) developed by the United States. In precision agriculture there are demands for static and cinematic positioning with distinct levels of accuracy for different applications; nevertheless cinematic performance data are not available as manufacturers of GPS receivers present only static performance information. For this reason it was developed an instrumented vehicle to test a methodology of performance evaluation of GPS receivers in kinematic conditions, which is representative to agricultural operations. A set of instrumentation was composed and used for collecting data under variable speed and rotation direction. Tests were conducted showing that the methodology allows to measure accuracy and precision, but improvements have to be implemented on the instrumentation equipment for long term tests.

Transformação de Helmert generalizada no posicionamento de alta precisão: fundamentação teórica e exemplificações

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Mitigating systematic errors for single frequency GPS receivers employing a penalized least squares methodology

Among the positioning systems that compose GNSS (Global Navigation Satellite System), GPS has the capability of providing low, medium and high precision positioning data. However, GPS observables may be subject to many different types of errors. These systematic errors can degrade the accuracy of the positioning provided by GPS. These errors are mainly related to GPS satellite orbits, multipath, and atmospheric effects. In order to mitigate these errors, a semiparametric model and the penalized least squares technique were employed in this study. This is similar to changing the stochastical model, in which error functions are incorporated and the results are similar to those in which the functional model is changed instead. Using this method, it was shown that ambiguities and the estimation of station coordinates were more reliable and accurate than when employing a conventional least squares methodology.

Geração de VRS a partir de modelos atmosféricos: Conceito, implementação e resultados

Nowadays, with the implantation of GNSS (Global Navigation Satellite System) reference station networks, several positioning techniques have been developed and/or improved. Using such kind of network data it is possible to model the GNSS distance dependent errors and to compute correction terms for the network region. Several methods have been developed to formulate the corrections terms from network stations data. A method that has been received a great attention is the Virtual Reference Station (VRS). The idea is that the VRS data resemble as much as possible a real receiver data placed in the same local. Therefore, the user has the possibility of using the VRS as if it were a real reference station in your proximities, and to accomplish the relative positioning with a single frequency receiver. In this paper it is described a different methodology applied to implement the VRS concept, using atmospheric models developed by Brazilian researchers. Besides, experiments for evaluating the quality of generated VRS are presented, showing the efficiency of the proposed method.

GPS ambiguity resolution and validation under multipath effects: Improvements using wavelets

Integer carrier phase ambiguity resolution is the key to rapid and high-precision global navigation satellite system (GNSS) positioning and navigation. As important as the integer ambiguity estimation, it is the validation of the solution, because, even when one uses an optimal, or close to optimal, integer ambiguity estimator, unacceptable integer solution can still be obtained. This can happen, for example, when the data are degraded by multipath effects, which affect the real-valued float ambiguity solution, conducting to an incorrect integer (fixed) ambiguity solution. Thus, it is important to use a statistic test that has a correct theoretical and probabilistic base, which has became possible by using the Ratio Test Integer Aperture (RTIA) estimator. The properties and underlying concept of this statistic test are shortly described. An experiment was performed using data with and without multipath. Reflector objects were placed surrounding the receiver antenna aiming to cause multipath. A method based on multiresolution analysis by wavelet transform is used to reduce the multipath of the GPS double difference (DDs) observations. So, the objective of this paper is to compare the ambiguity resolution and validation using data from these two situations: data with multipath and with multipath reduced by wavelets. Additionally, the accuracy of the estimated coordinates is also assessed by comparing with the ground truth coordinates, which were estimated using data without multipath effects. The success and fail probabilities of the RTIA were, in general, coherent and showed the efficiency and the reliability of this statistic test. After multipath mitigation, ambiguity resolution becomes more reliable and the coordinates more precise. © Springer-Verlag Berlin Heidelberg 2007.

Estimativa e análise de índices de irregularidades da ionosfera utilizando dados GPS de redes ativas

Observable GNSS (Global Navigation Satellite System) are affected by systematic errors due to free electrons present in the ionosphere. The error associated with the ionosphere depends on the Total Electron Content (TEC), which is influenced by several variables: solar cycle, season, local time, geomagnetic activity and geographic location. The GPS (Global Positioning System), GLONASS (Global Orbiting Navigation Satellite System) and Galileo dual frequency receivers allow the calculation of the error that affects the GNSS observables and the TEC. Using the rate of change of TEC (ROT - Rate of TEC) indices that indicate irregularities of the ionosphere can be determined, allowing inferences about its behavior. Currently it is possible to perform such studies in Brazil, due to the several Active Networks available, such as RBMC/RIBaC (Rede Brasileira de Monitoramento Contínuo/Rede INCRA de Bases Comunitárias) and GNSS Active Network of São Paulo. The proposed research aimed at estimating and analysing of indexes of irregularities of the ionosphere, besides supplying the geosciences of information about the behavior of the ionosphere.

Análise de wavelets para detecção e correção do multicaminho no posicionamento relativo GNSS estático e cinemático

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Modelagem neutrosférica sobre a América do Sul baseada em PNT e assimilação de dados locais e robusta avaliação utilizando observações GNSS

Pós-graduação em Ciências Cartográficas - FCT

Método dos mínimos quadrados com penalidades: aplicação no posicionamento relativo GPS

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)