François Fund

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Observations GPS et retards troposphériques : modélisations et application aux effets de surcharge océanique dans l'ouest de la France

L’Ouest de la France est soumis a des deplacements lithospheriques dont l’une des origines est la... more L’Ouest de la France est soumis a des deplacements lithospheriques dont l’une des origines est la maree oceanique. Les effets sont notamment importants dans le Finistere et dans la baie du Mont-Saint-Michel, ou les coefficients des marees sont parmi les plus eleves dans le monde. Ces deplacements periodiques qui sont observes aussi bien dans la direction verticale qu’horizontale, affectent la lithosphere continentale sur de grandes longueurs d’onde. Les deplacements du sol peuvent atteindre des amplitudes de l'ordre de 2 cm au Mans et jusqu’a 10 cm a Brest. Aujourd’hui, le developpement des reseaux GPS temps reel permanents comme TERIA complete les reseaux permanents existants et represente un outil indispensable pour l’observation precise des deplacements d’origine crustale. La densite geographique de ces reseaux, mais aussi la quantite des donnees enregistrees depuis leurs mises en place, permettent d’ores et deja d’entamer des recherches prometteuses dans ce sens. Neanmoins, ...

Modélisations des retards troposphériques pour les observations GPS et impacts sur l'estimation de la hauteur ellipsoïdale

Assessment of ionospheric and tropospheric corrections for PPP-RTK

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Ocean Loading in Brittany, Northwest France: Impact of the GPS Analysis Strategy

In this contribution, we analyze the impact of different GPS processing strategies on ocean tide ... more In this contribution, we analyze the impact of different GPS processing strategies on ocean tide loading estimation. We use continuous GPS data acquired during a 4-month campaign performed in 2004 in Brittany, Northwest France. Since the expected geodynamical signal in the estimated positions is exceeding the typical GPS data analysis noise, this data set can be used to compare the results obtained with different analysis software packages. Moreover, in this specific case we need short sub-daily solutions to study short-period signals instead of classical 24 h-solutions. The GPS capability for measuring 3D ocean tide loading deformation has already been assessed, but since we are looking for the finest signal as the one induced by the shallow water constituents, it is essential to be sure that the position time series represent a geodynamical signal and are not biased by the data processing strategy used. To analyze the possible effect of the methodology used on the geodynamical res...

A New GNSS-PPP/INS Data Fusion for Global Infrastructure-less Safe Train Positioning

Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019), 2019

In France, 33 000 kilometers of tracks are used daily by 15 000 trains, inducing extraordinary ma... more In France, 33 000 kilometers of tracks are used daily by 15 000 trains, inducing extraordinary maintenance costs. A new approach for train localization is mandatory by railway operators as part of European standardization European Rail Traffic Management System. Physical railway signaling has to be removed and capacity of existing lines has to be increased by reducing the distance between the trains. That objectives require the right identification of the railway track and the capacity to localize the train with an along-track accuracy of less than 5m, with a high level of safety. The NRTK technique provides an accurate positioning but has several drawbacks to answer to the other requirements. Mainly, it is based on a high number of CORS and a complex bidirectional process inducing a problem of certification. Geoflex is a new operator of global real-time and post-processed corrections based on the PPP CNES technology. It can provide positions with a horizontal accuracy up to 4cm (95...

Assessment of the FES2004 Derived OTL Model in the West of France and Preliminary Results About Impacts of Tropospheric Models

Ocean Tide Loading displacements in the West of France are among the largest in the world. In ord... more Ocean Tide Loading displacements in the West of France are among the largest in the world. In order to contribute to the improvement of tidal models for GPS processing, we estimate ocean tides in this area with static GPS. Observations recorded over at least 1.5 years are used from ~60 stations with typical separation distances of 50–80 km. Previous studies showed the consistency of the FES2004 model of OTL displacements with GPS estimates of the main semi-diurnal tides in the North of Brittany. We extend this study over a larger spatial scale and investigate the ten main tides. The largest differences between GPS estimates and modeled values are obtained for the M2, K1, and K2 tides. We attribute the discrepancies of K1 and K2 tides to multipath effects. Preliminary results about the impact of using current annual empirical tropospheric models instead of 6 h-period data derived from ECMWF data and provided by TU Vienna are presented.

Influence of SSR atmospheric corrections in PPP-RTK processing parameters

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Modeling tropospheric wet delays with dense and sparse network configurations for PPP-RTK

Precise Point Positioning (PPP) is a well-known technique of positioning by Global Navigation Sat... more Precise Point Positioning (PPP) is a well-known technique of positioning by Global Navigation Satellite Systems (GNSS) that provides accurate solutions. With the availability of real-time precise orbit and clock products provided by the International GNSS Service (IGS) and by individual analysis centers such as Centre National d’Etudes Spatiales through the IGS Real-Time Project, PPP in real time is achievable. With such orbit and clock products and using dual-frequency receivers, first-order ionospheric effects can be eliminated by the ionospheric-free combination. Concerning the tropospheric delays, the Zenith Hydrostatic Delays can be quite well modeled, although the Zenith Wet Delays (ZWDs) have to be estimated because they cannot be mitigated by, for instance, observable combinations. However, adding ZWD estimates in PPP processing increases the time to achieve accurate positions. In order to reduce this convergence time, we (1) model the behavior of troposphere over France usi...

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Estimation des déplacements causés par la surcharge océanique dans l'Ouest de la France à l'aide des réseaux GPS permanents

Validity and behaviour of tropospheric gradients estimated by GPS in Corsica

Advances in Space Research

Estimation of tropospheric gradients in GNSS data processing is a well-known technique to improve... more Estimation of tropospheric gradients in GNSS data processing is a well-known technique to improve positioning (e.g. Bar-Sever et al., 1998; Chen and Herring, 1997). More recently, several authors also focused on the estimation of such parameters for meteorological studies and demonstrated their potential benefits (e.g. Champollion et al., 2004). Today, they are routinely estimated by several global and regional GNSS analysis centres but they are still not yet used for operational meteorology.

Impact of loading phenomena on velocity field computation from GPS campaigns: application to ResPyr GPS campaign in the Pyrenees

To quantify the present-day tectonic deformation in the Pyrenees mountain range area where the se... more To quantify the present-day tectonic deformation in the Pyrenees mountain range area where the seismic activity is continuous and moderate, different GPS ResPyr campaigns were performed between 1995 and 2008. Considering the expected rate of deformation of about 1 mm/yr, we can wonder what would be the impact of the different loading effects on velocity field computed from GPS campaigns and therefore on the characterization of the deformation.

Improved Constraints on Models of Glacial Isostatic Adjustment: A Review of the Contribution of Ground-Based Geodetic Observations

Surveys in Geophysics, 2010

The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority ne... more The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority need in climate studies, largely due to the potential of the Gravity Recovery and Climate Experiment (GRACE) data to be used to determine accurate and continent-wide assessments of ice mass change and hydrology. However, modelled GIA is

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