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How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

How the GNSS reference stations work – C.O.R.S. ?

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Permanent stations, how does it work?

Real-time centimetric positioning is based on data collected by permanent GNSS stations, also known as C.O.R.S (Continuous Operating Reference Station)…

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All PPP, RTK, NRTK and PPP-RTK positioning methods use these permanent reference stations, alone or in networks. How are they equipped and how do they work? How can we obtain a continuous service?

High-tech equipment

Surveyors, GIS users, engineers, scientists and the general public who collect GNSS data can now use C.O.R.S. data to improve the accuracy of their positions.

In just a few years, permanent stations have been installed all over the world. They now form vast interconnected networks that have enabled immense progress to be made. This development benefits both the scientific and service sectors.

A permanent C.O.R.S. station combines :

a Choke Ring*GNSS antenna and a coaxial cable linking the GNSS antenna to the GNSS receiver,
a multi-frequencyGNSS receiver ,
one or more telecommunications devices.
remote management equipment for remote restarting of the equipment
a power supply.

This technology has undergone a profound evolution. The latest multi-frequency receivers support all the world’s GNSS constellations, with more than 550 channels. These include the GPS and GLONASS constellations, as well as GALILEO and BEIDOU. There are also regional systems such as QZSS and SBAS.

* The Choke Ring antenna is a robust antenna that minimises multipath (GNSS signal deviation) or reflections against surrounding surfaces. It also allows a small variation in the position of the phase centre, for which very high-precision calibrations are available. (see photo opposite)

PARD GNSS station of the RESIF-RENAG network, municipality of Pardailhan (Hérault) @Sandrine Baudin

UNAVCO - BERP Station, Kohler Glacier West Antarctica

Choosing the installation site

The installation site must be free of any obstacles. In other words, no masks that could prevent or attenuate GNSS signal reception or cause multipath. Generally, the GNSS antenna is installed on an open mountain site or solidly fixed to the roof of a permanent building. In other words, a building that does not have any unusual movements due to tectonic or climatic movements. (This excludes buildings with sheet metal structures, for example, which deform with changes in temperature)

The antenna site has a clear 360° horizon, above an elevation angle of 5°. Some GPS stations used for geodesy applications have their own infrastructure. This is to ensure that no movement linked to the environment interferes with data acquisition. In France, this is the case for RENAG stations, and internationally for UNAVCO network stations.

Station PBO - Earthscope Chronicles @UNAVCO

How it works

A permanent GNSS or C.O.R.S station observes all the signals emitted by the global positioning constellations 24 hours a day, 7 days a week. For Europe, this includes the American GPS constellation, the Russian GLONASS constellation, the European GALILEO constellation and the Chinese BEIDOU constellation.

The signals picked up by GNSS stations are communicated by various means of telecommunications to servers, either in real time or in delayed time (generally via the Internet). (generally via the Internet)

As far as processing by the computing centre is concerned, the navigation message data from the main positioning constellations (ephemeris, system status, etc.) are not sufficient on their own to achieve high accuracy. To achieve centimetre-precision positioning, a number of variables need to be taken into account: precise orbits and reference system as well as Earth orientation parameters.

The data corrected by the computing centre is either transmitted to users in real time (RTCM format for TERIA) or stored to be made available for post-processing. In the latter case, the data is generally in Rinex format. The IGN’s RGP website, for example, provides this type of data: http://rgp.ign.fr

The IGS(International GNSS Service) network uses GNSS data from permanent stations to define coordinate systems around the world, through the various ITRF projects. The accuracies now obtained are down to a few millimetres. What’s more, they make it possible to measure the tectonic displacements of each station very accurately, and to calculate plate displacements as a result.

Continuous service

Maintenance of permanent GNSS stations is essential . Correct use of the correction calculation software is just as important. It provides users with a superior quality of service.

A service interruption could have major consequences for users who are working in the field. Every means must be put in place to prevent or resolve any disruption to the service.

M.C.O: Maintenance in Operational Condition

At TERIA, the M.C.O. (Maintenance in Operational Conditions) service is a priority. Engineers and experts are dedicated to ensuring that reference stations operate to the highest quality standards. A veritable ” task force “, this team is dedicated to providing a rapid solution in all conditions. Numerous IT interfaces provide real-time visibility of the status of the stations on site. These immediately alert the technical teams as soon as there is a change in status.

A troubleshooting protocol is then launched to quickly determine what action needs to be taken:

remote restarts
urgent on-site intervention
(replacement, configuration…)

99.8%

The density of reference stations in the TERIA GNSS network, combined with the efforts of our technical teams, have guaranteed an availability rate of over 99% since 2012. (ISO 9001 certification)

The M.C.O. indicators enable continuous improvement. They also enable us to identify possible improvements in each area. This is a necessary step in implementing preventive actions on all the sites. A global register lists all the actions and events that have occurred on the GNSS network of reference stations.

Each event is qualified according to its nature:

Electrical
Telephone network
Condition of equipment
etc.

TERIA experts constantly monitor technical developments. This includes monitoring technological developments and improvements made possible by the latest firmware versions deployed by GNSS receiver manufacturers.

The TERIA teams are committed to providing a continuous high-quality service and personalised support to each customer.