Specific action Rénag / Permanent national GNSS network

Outline

Epos-France’s Action Spécifique Rénag is part of the Groupe Thématique Géodésie GNSS. It corresponds to the Epos-France IR contribution of the Service National d’Observation Rénag, SNO of the Action Nationale d’Observation (ANO) 3 “Géodésie-Gravimétrie” of CNRS-Insu. This SNO brings together academic and non-academic partners who operate and use a set of permanent GNSS stations in mainland France, as well as a network of semi-permanent markers. AS Rénag is responsible for coordinating the implementation and maintenance of these instruments.

In addition to data from its own network, Rénag hosts and distributes data from the private Orphéon network under an agreement with “Geodata diffusion”. The distribution, conservation and scientific use of data from these networks are managed by Rénag, in particular within the GNSS Information System transverse thematic action for aspects of data distribution in the broadest sense.

A number of products (notably position time series and secular velocities of network stations) are computed from observation data, some of which are disseminated via EPOS-GNSS services. Scientific discussions and actions are organized around these products, in particular through benchmarking exercises for data analysis in a low-deformation context.

Objectives

The network maintained by Rénag is dedicated to scientific research and Earth observation in the fields of internal and external geophysics and geodesy. The scientific objectives of the Rénag specific action are in line with those of the SNO of the same name, namely :

• to quantify the slow tectonic deformation in France, to establish the link with the moderate seismicity recorded and to constrain the geological and physical models explaining the current deformation. These measurements help to assess the seismic hazard in France; 
• to measure variations in sea level by separating vertical displacements on land from climatic contributions in tide gauge records using GNSS stations co-located with tide gauges, particularly in mainland France; 
• to measure the water vapour content of the troposphere to analyse heavy rainfall events and to assimilate these measurements in operational weather forecasting models. These stable measurements over long periods also contribute to the study of climate change; 
• to characterise transient movements linked to oceanic and atmospheric overloads, as well as hydrological loads;
• to explore new GNSS applications such as measuring snow height or soil moisture content using reflectometry, measuring ionospheric activity, etc; 
• to contribute to a stable, high-frequency reference framework for monitoring rapid geophysical phenomena: earthquakes, glaciers, landslides, offshore positioning, etc.