A dense GNSS meteorological network for observing deep convection in the Amazon

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

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)

Tackling ionospheric scintillation threat to GNSS in Latin America

Scintillations are rapid fluctuations in the phase and amplitude of transionospheric radio signals which are caused by small-scale plasma density irregularities in the ionosphere. In the case of the Global Navigation Satellite System (GNSS) receivers, scintillation can cause cycle slips, degrade the positioning accuracy and, when severe enough, can even lead to a complete loss of signal lock. Thus, the required levels of availability, accuracy, integrity and reliability for the GNSS applications may not be met during scintillation occurrence; this poses a major threat to a large number of modern-day GNSS-based applications. The whole of Latin America, Brazil in particular, is located in one of the regions most affected by scintillations. These effects will be exacerbated during solar maxima, the next predicted for 2013. This paper presents initial results from a research work aimed to tackle ionospheric scintillation effects for GNSS users in Latin America. This research is a part of the CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project, co-funded by the EC Seventh Framework Program and supervised by the GNSS Supervisory Authority (GSA), which aims to develop and test ionospheric scintillation countermeasures to be implemented in multi-frequency, multi-constellation GNSS receivers.

Enabling Techniques and Algorithms for Integrated Communication and Navigation Satellite Systems

This thesis presents the outcomes of my Ph.D. course in telecommunications engineering. The focus of my research has been on Global Navigation Satellite Systems (GNSS) and in particular on the design of aiding schemes operating both at position and physical level and the evaluation of their feasibility and advantages. Assistance techniques at the position level are considered to enhance receiver availability in challenging scenarios where satellite visibility is limited. Novel positioning techniques relying on peer-to-peer interaction and exchange of information are thus introduced. More specifically two different techniques are proposed: the Pseudorange Sharing Algorithm (PSA), based on the exchange of GNSS data, that allows to obtain coarse positioning where the user has scarce satellite visibility, and the Hybrid approach, which also permits to improve the accuracy of the positioning solution. At the physical level, aiding schemes are investigated to improve the receiver’s ability to synchronize with satellite signals. An innovative code acquisition strategy for dual-band receivers, the Cross-Band Aiding (CBA) technique, is introduced to speed-up initial synchronization by exploiting the exchange of time references between the two bands. In addition vector configurations for code tracking are analyzed and their feedback generation process thoroughly investigated.

GNSS interference management techniques against malicious attacks

This thesis collects the outcomes of a Ph.D. course in Telecommunications Engineering and it is focused on the study and design of possible techniques able to counteract interference signal in Global Navigation Satellite System (GNSS) systems. The subject is the jamming threat in navigation systems, that has become a very increasingly important topic in recent years, due to the wide diffusion of GNSS-based civil applications. Detection and mitigation techniques are developed in order to fight out jamming signals, tested in different scenarios and including sophisticated signals. The thesis is organized in two main parts, which deal with management of GNSS intentional counterfeit signals. The first part deals with the interference management, focusing on the intentional interfering signal. In particular, a technique for the detection and localization of the interfering signal level in the GNSS bands in frequency domain has been proposed. In addition, an effective mitigation technique which exploits the periodic characteristics of the common jamming signals reducing interfering effects at the receiver side has been introduced. Moreover, this technique has been also tested in a different and more complicated scenario resulting still effective in mitigation and cancellation of the interfering signal, without high complexity. The second part still deals with the problem of interference management, but regarding with more sophisticated signal. The attention is focused on the detection of spoofing signal, which is the most complex among the jamming signal types. Due to this highly difficulty in detect and mitigate this kind of signal, spoofing threat is considered the most dangerous. In this work, a possible techniques able to detect this sophisticated signal has been proposed, observing and exploiting jointly the outputs of several operational block measurements of the GNSS receiver operating chain.

A consistent combination of GNSS and SLR with minimum constraints

In this article, the realization of a global terrestrial reference system (TRS) based on a consistent combination of Global Navigation Satellite System (GNSS) and Satellite Laser Ranging (SLR) is studied. Our input data consists of normal equation systems from 17 years (1994– 2010) of homogeneously reprocessed GPS, GLONASS and SLR data. This effort used common state of the art reduction models and the same processing software (Bernese GNSS Software) to ensure the highest consistency when combining GNSS and SLR. Residual surface load deformations are modeled with a spherical harmonic approach. The estimated degree-1 surface load coefficients have a strong annual signal for which the GNSS- and SLR-only solutions show very similar results. A combination including these coefficients reduces systematic uncertainties in comparison to the singletechnique solution. In particular, uncertainties due to solar radiation pressure modeling in the coefficient time series can be reduced up to 50 % in the GNSS+SLR solution compared to the GNSS-only solution. In contrast to the ITRF2008 realization, no local ties are used to combine the different geodetic techniques.We combine the pole coordinates as global ties and apply minimum constraints to define the geodetic datum. We show that a common origin, scale and orientation can be reliably realized from our combination strategy in comparison to the ITRF2008.

Characterization of Cavities Using the GPR, LIDAR and GNSS Techniques

The study of the many types of natural and manmade cavities in different parts of the world is important to the fields of geology, geophysics, engineering, architectures, agriculture, heritages and landscape. Ground-penetrating radar (GPR) is a noninvasive geodetection and geolocation technique suitable for accurately determining buried structures. This technique requires knowing the propagation velocity of electromagnetic waves (EM velocity) in the medium. We propose a method for calibrating the EM velocity using the integration of laser imaging detection and ranging (LIDAR) and GPR techniques using the Global Navigation Satellite System (GNSS) as support for geolocation. Once the EM velocity is known and the GPR profiles have been properly processed and migrated, they will also show the hidden cavities and the old hidden structures from the cellar. In this article, we present a complete study of the joint use of the GPR, LIDAR and GNSS techniques in the characterization of cavities. We apply this methodology to study underground cavities in a group of wine cellars located in Atauta (Soria, Spain). The results serve to identify construction elements that form the cavity and group of cavities or cellars. The described methodology could be applied to other shallow underground structures with surface connection, where LIDAR and GPR profiles could be joined, as, for example, in archaeological cavities, sewerage systems, drainpipes, etc.

Avaliação da qualidade das medições fotogramétricas da versão integrada do software livre E-FOTO.

Na década de 90 com o aumento da capacidade de processamento e memória dos computadores, surgiu a fotogrametria digital, que tem como objetivo principal o mapeamento automático das feições naturais e artificiais do terreno, utilizando a imagem fotogramétrica digital como fonte primária de dados. As soluções fotogramétricas se tornaram mais compactas e versáteis. A estação fotogramétrica digital educacional E-FOTO é um projeto multidisciplinar, em desenvolvimento no laboratório de Fotogrametria Digital da Universidade do Estado do Rio de Janeiro, que se baseia em dois pilares: autoaprendizado e gratuidade. Este trabalho tem o objetivo geral de avaliar a qualidade das medições fotogramétricas utilizando a versão integrada 1.0β do E-FOTO. Para isso foram utilizados dois blocos de fotografias de regiões distintas do planeta: um bloco de fotografias (2005) do município de Seropédica-RJ e um bloco de fotografias antigas (1953) da região de Santiago de Compostela, na Espanha. Os resultados obtidos com o E-FOTO foram comparados com os resultados do software comercial de fotogrametria digital Leica Photogrammetry Suite (LPS 2010) e com as coordenadas no espaço-objeto de pontos medidos com posicionamento global por satélite (verdade de campo). Sendo possível avaliar as metodologias dos softwares na obtenção dos parâmetros das orientações interior e exterior e na determinação da exatidão das coordenadas no espaço-objeto dos pontos de verificação obtidas no módulo estereoplotter versão 1.64 do E-FOTO. Os resultados obtidos com a versão integrada 1.0β do E-FOTO na determinação dos parâmetros das orientações interior e exterior e no cálculo das coordenadas dos pontos de verificação, sem a inclusão dos parâmetros adicionais e a autocalibração são compatíveis com o processamento realizado com o software LPS. As diferenças dos parâmetros X0 e Y0 obtidos na orientação exterior com o E-FOTO, quando comparados com os obtidos com o LPS, incluindo os parâmetros adicionais e a autocalibração da câmara fotogramétrica, não são significativas. Em função da qualidade dos resultados obtidos e de acordo com o Padrão de Exatidão Cartográfica, seria possível obter um documento cartográfico Classe A em relação à planimetria e Classe B em relação à altimetria na escala 1/10.000, com o projeto Rural e Classe A em relação à planimetria e Classe C em relação à altimetria na escala 1/25.000, com o Projeto Santiago de Compostela. As coordenadas tridimensionais (E, N e H) dos pontos de verificação obtidas fotogrametricamente no módulo estereoplotter versão 1.64 do E-FOTO, podem ser consideradas equivalentes as medidas com tecnologia de posicionamento por satélites.

Automated identification and tracking of polar-cap plasma patches at solar minimum

A method of automatically identifying and tracking polar-cap plasma patches, utilising data inversion and feature-tracking methods, is presented. A well-established and widely used 4-D ionospheric imaging algorithm, the Multi-Instrument Data Assimilation System (MIDAS), inverts slant total electron content (TEC) data from ground-based Global Navigation Satellite System (GNSS) receivers to produce images of the free electron distribution in the polar-cap ionosphere. These are integrated to form vertical TEC maps. A flexible feature-tracking algorithm, TRACK, previously used extensively in meteorological storm-tracking studies is used to identify and track maxima in the resulting 2-D data fields. Various criteria are used to discriminate between genuine patches and "false-positive" maxima such as the continuously moving day-side maximum, which results from the Earth's rotation rather than plasma motion. Results for a 12-month period at solar minimum, when extensive validation data are available, are presented. The method identifies 71 separate structures consistent with patch motion during this time. The limitations of solar minimum and the consequent small number of patches make climatological inferences difficult, but the feasibility of the method for patches larger than approximately 500 km in scale is demonstrated and a larger study incorporating other parts of the solar cycle is warranted. Possible further optimisation of discrimination criteria, particularly regarding the definition of a patch in terms of its plasma concentration enhancement over the surrounding background, may improve results.

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.

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.

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

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Grade ionosférica para aplicações em posicionamento e navegação com GNSS

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

O entroncamento das políticas agrárias no Maranhão: encontros e desencontros institucionais na Microrregião Geográfica de Itapecuru Mirim

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)