Personne :
Cocard, Marc

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Université Laval. Département des sciences géomatiques
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Résultats de recherche

Voici les éléments 1 - 10 sur 12
  • Publication
    A sequential network approach for estimating GPS satellite phase biases at the PPP-AR producer-side
    (Springer, 2018-04-11) Santerre, Rock; Kamali, Omid; Cocard, Marc
    Ambiguity resolution (AR) in precise point positioning (PPP) requires precise satellite orbit, clocks, and phase biases corrections. Satellite phase biases are fractional hardware corrections which help to retrieve the un-differenced integer carrier phase ambiguities. Satellite corrections can be obtained from the international GNSS service (IGS) or estimated by correction providers called producer-side. We introduce a new PPP-AR observation model and a new sequential network algorithm (SNA) to estimate satellite phase biases. The new model is fully compatible with standard IGS satellite correction products, and it takes advantage of currently available IGS global ionosphere maps to improve the stability of corrections estimation. Furthermore, the proposed model is full-rank per-frequency and per-site and this method simplifies the integration of any additional frequency or site observables in the system of equations. The per-site satellite phase biases method allows users to customize their network solution. In many cases, users only have to estimate the phase biases of a few satellites estimated by few stations to resolve ambiguities of their observed satellites. The novel two-step algorithm provides a good balance between the computational burden, the computer memory load, the efficiency of handling parameters, and the precise estimation of correction parameters. The proposed PPP-AR model and the SNA performance is then validated by estimating satellite phase biases with 1 year of GPS data from a sub-network of IGS stations. A rigorous a posteriori statistical test is performed using data from an independent GPS network. As a result, the precision of WL and L1 ambiguities was improved significantly with the confidence level of P > 99.99% by applying the estimated phase bias corrections to phase observables.
  • Publication
    GPS interactive time series analysis software
    (John Wiley & Sons, 2012-10-12) Santerre, Rock; Goudarzi, Mohammad Ali; Cocard, Marc; Woldai, Tsehaie
    Time series analysis is an important part of geodetic and geodynamic studies, especially when continuous GPS observations are used to explore areas with a low rate of deformation. In this domain, having precise and robust tools for processing and analyzing position time series is a prerequisite. To meet this requirement, a new software package called GPS Interactive Time Series Analysis was developed using the MATLAB language. Along with calculating basic statistics and quality parameters such as mean and variance, the software is capable of importing and visualizing different time series formats, determining and removing jumps and outliers, interpolating data, and producing numerical and publication quality graphical outputs. Furthermore, bivariate statistical analysis (such as correlation coefficients, curvilinear and nonlinear regression), residual analysis, and spectral analysis (such as auto-spectrum, Lomb–Scargle spectrum, evolutionary power spectrum, and wavelet power spectrum) form the main analysis features of the software.
  • Publication
    La formation et la recherche en acquisition et traitement de données géomatiques au Département des sciences géomatiques de l’Université Laval
    (Association canadienne des sciences géomatiques, 2007-09-01) Boulianne, Michel; Santerre, Rock; Mostafavi, Mir Abolfazl; Daniel, Sylvie; Viau, Alain; Cocard, Marc
    De nombreux projets de recherche en acquisition et traitement de données géomatiques ont cours au Département des sciences géomatiques de l’Université Laval. Les projets se sont particulièrement diversifiés ces dernières décennies. Une description des principaux projets passés et actuels est présentée. Ceux-ci se rapportent principalement aux domaines du positionnement par satellites, de la photogrammétrie, de l’imagerie numérique et de la télédétection. Ces projets couvrent autant les aspects fondamentaux en géomatique que des applications concrètes et novatrices dans divers domaines (agriculture, architecture, archéologie, auscultation topographique, performances sportives, etc.). Finalement, quelques projets intégrateurs qui allient plusieurs disciplines de la géomatique sont présentés et démontrent la synergie de ces disciplines d’acquisition et de traitement de données géomatiques.
  • Publication
    EPC : Matlab software to estimate Euler pole parameters
    (John Wiley & Sons, 2013-11-22) Santerre, Rock; Goudarzi, Mohammad Ali; Cocard, Marc
    The estimation of Euler pole parameters has always been an important issue in global tectonics and geodynamics studies. In addition, the increasing number of permanent GPS stations and the ease of access to their data, along with advances in computers, promise new methods and tools for the estimation and the quantitative analysis of Euler pole parameters. Therefore, we developed the Euler pole calculator software using a set of mathematical algorithms based on the model of tectonic plate motion on a spherical surface. The software is able to calculate the expected velocities for any points located on the earth’s surface given the relevant Euler pole parameters and to estimate the Euler pole parameters given the observed velocities of a set of sites located on the same tectonic plate. Mathematical algorithms and functions of the software are explained in detail.
  • Publication
    Research activities in precise positioning at Laval University
    (Canadian Institute of Geomatics, Vol. 66, (2), 89-101 (2012 ), 2012-03-01) Santerre, Rock; Lamothe, Philippe; Macias-Valadez, Daniel; Kamali, Omid; Bourgon, Stéphanie.; Kirouac, Valérie; Prat, Yann; Cocard, Marc
    This review paper summarises the recent, on-going, and future research activities in precise positioning at Laval University. The projects undertaken by the GPS and Geodesy Research Group are presented following three main research topics. The first one deals with the use of precise positioning for deformation monitoring of engineering structures. The study of ice forces on dams using a robotic total station and the improvement of GPS height determination using multiple GPS antennas linked to a single receiver with calibrated fiber optics are presented. A second topic of research is the crustal deformation of the Charlevoix seismic zone in Quebec. This study uses GPS and levelling techniques and involves an investigation of the temporal stability of the GPS permanent stations available in the surrounding area. Finally, research on single GPS receiver positioning techniques is presented, namely, Precise Point Positioning (PPP) and Time Relative Positioning (TRP).
  • Publication
    A crustal deformation study of the Charlevoix seismic zone in Quebec.
    (Canadian Institute of Geomatics., 2010-09-01) Santerre, Rock; Lamothe, Philippe; Cocard, Marc; Mazzotti, Stéphane
    First order spirit levelling and high precision GPS measurements have been used to quantify local deformations caused mainly by postglacial rebound in the Charlevoix seismic zone, the region with the highest concentrated seismic activity in eastern Canada. In this paper, part of the Canadian first order vertical network, measured from 1909 to 1991, is analyzed for repeating levelling lines. In addition, a part of a first order geodetic network along the Saint Lawrence River surveyed by GPS in 1991 and 2005, is processed. The coordinate changes of these geodetic points allows for the determination of horizontal and vertical velocities leading to information about the crustal deformation of this region. The results show a southeast drift trend in the horizontal, and general uplift trend in the vertical. These agree well with previous GPS surveys conducted on Canadian Base Network (CBN) pillars in eastern Canada and with geophysical postglacial rebound (PGR) models.
  • Publication
    3D modeling of the tropospheric refractivity using a permanent GPS network.
    (Canadian Institute of Geomatics., 2007-12-01) Santerre, Rock; Macias-Valadez, Daniel; Cocard, Marc
    Tropospheric delay inherent to GPS signals negatively impacts positioning precision. However, it can also provide information about the state of the troposphere, which may be useful for several meteorological applications. With a permanent GPS network, and using the estimated slant wet delays (SWD) between receivers and satellites, it is possible to develop a 3D model of the wet refractivity within the network and, for this purpose, we propose to use a 3D Taylor’s series development. To test this approach, a permanent network of 43 GPS stations in Switzerland has been used to estimate the SWD and use these values as input data to the proposed model. Using this model, it is possible to estimate zenith wet delay (ZWD) for a random 3D location within the network. The resulting ZWD can then be used to correct tropospheric delays of any additional roving GPS receiver not being part of the network. The wet refractivity values obtained with the model were validated against meteorological data gathered at independent meteorological stations within Switzerland.
  • Publication
    Single GPS receiver time-relative positioning with loop misclosure corrections.
    (Springer, 2005-10-06) Santerre, Rock; Bourgon, Stéphanie.; Balard, Nicolas.; Cocard, Marc
    Time-relative positioning makes use of observations taken at two different epochs and stations with a single global positioning system (GPS) receiver to determine the position of the unknown station with respect to the known station. The limitation of this method is the degradation over time of the positioning accuracy due to the temporal variation of GPS errors (ionospheric delay, satellite clock corrections, satellite ephemerides, and tropospheric delay). The impact of these errors is significantly reduced by adding to the one-way move from the known to the unknown station, a back move to the known station. A loop misclosure is computed from the coordinates obtained at the known station at the beginning and at the end of the loop, and is used to correct the coordinates of the unknown station. The field tests, presented in this paper, show that using the loop misclosure corrections, time-relative positioning accuracy can be improved by about 60% when using single frequency data, and by about 40% with dual frequency data. For a 4-min processing interval (an 8-min loop) and a 95% probability level, errors remain under 20 cm for the horizontal components and 36 cm for the vertical component with single frequency data; and under 11 cm for the horizontal components and 29 cm for the vertical component with dual frequency data.
  • Publication
    Estimating Euler pole parameters for eastern Canada using GPS velocities
    (Taylor & Francis, 2015-12-17) Santerre, Rock; Goudarzi, Mohammad Ali; Cocard, Marc
    Eastern Canada is characterized by many intraplate earthquakes mostly concentrated along the Saint Lawrence River and Ottawa River valleys. After the rigid plate rotation of North America, the glacial isostatic adjustment (GIA) is by far the largest source of geophysical signal in eastern Canada. We estimate a set of Euler pole parameters for this area using a velocity field of 19 continuously operating GPS stations out of 112, and show that they are different from the overall rotation of the North American plate. This difference potentially reflects local stresses in this seismic region, and the difference in intraplate velocities between the two flanks of the Saint Lawrence River valley accumulate stress along the river.
  • Publication
    Accès libre
    Noise behavior in CGPS position time series : the eastern North America case study
    (Versita, 2015-09-07) Santerre, Rock; Goudarzi, Mohammad Ali; Cocard, Marc
    We analyzed the noise characteristics of 112 continuously operating GPS stations in eastern North America using the Spectral Analysis and the Maximum Likelihood Estimation (MLE) methods. Results of both methods show that the combination ofwhite plus flicker noise is the best model for describing the stochastic part of the position time series. We explored this further using the MLE in the time domain by testing noise models of (a) powerlaw, (b)white, (c)white plus flicker, (d)white plus randomwalk, and (e) white plus flicker plus random-walk. The results show that amplitudes of all noise models are smallest in the north direction and largest in the vertical direction. While amplitudes of white noise model in (c–e) are almost equal across the study area, they are prevailed by the flicker and Random-walk noise for all directions. Assuming flicker noise model increases uncertainties of the estimated velocities by a factor of 5–38 compared to the white noise model.