by W. Gurtner, Astronomical Institute - University of Bern - May 1995

1. Introduction

At the EUREF Symposium in Warsaw, 8-11 June 1994, the Technical Working Group presented a proposal for the establishment of a network of permanent GPS stations in Europe. This network should in fact consist of a selection of those permanent stations that have been or will be installed

  • as part of local networks established for the purpose of Realtime Differential GPS (DGPS)
  • as part of local or regional networks established for monitoring geodynamical phenomenae
  • as permanent reference stations for national reference systems
  • for global tracking purposes and global reference system definition in the framework of the International GPS Service for Geodynamics (IGS)
  • for any other purposes

and the data of which are made available to EUREF by the responsible organizations.

Apart from the stations themselves such a permanent network needs the following components :

Operational Centres (OC) :

They perform data validation, data conversion to RINEX, data compression, data upload to a data centre through Internet. For some sites the OC are identical with the institution responsible for the respective sites.

Local Data Centres (LDC) :

They collect the data of all stations of the respective network and distribute them to the (local) users. For many of the local networks the Local Data Centre will be identical with their Operational Centre. If the local network takes part of the regional or global network (EUREF, IGS), the LDC will forward (a selection of) the data to the Regional Data Centre.

Regional Data Centre (RDC) :

It collects all the data needed for the regional processing and makes it available to the users, especially to the European Analysis Centre(s)

Regional Analysis Centres :

They process part or all of the European data to generate a continuous record of positions and other parameters (e.g. troposphere or ionosphere)

A Network Coordinator

responsible for the coordination of all activities related to this EUREF Permanent Network

With the exception of the Network Coordinator all components more or less already exist, either within the organizations for the primary objectives of the local network, or as part of the International GPS Service for Geodynamics.

This paper describes the requirements the stations and Operational Centres have to meet to be included into the EUREF Permanent Network.

2. Requirements for Permanent GPS Stations

As the user of the network will be mainly interested in the data and the necessary auxiliary informations about the tracking sites, we do not distiguish too strictly between the activities and responsibilities of the Stations and the Operational Centres.

As EUREF would like to make use of existing networks it is of course not possible to set up very strict rules and guidelines. This paper is rather intended to be used to check if a station or part of a local network can actually be used for the EUREF Network.

Many of these guidelines are identical with those in use within the International GPS Service for Geodynamics.

2.0 Sites

It is recommended to collocate permanent GPS sites with observatories of other physical phenomenae such as

  • observatories of other space techniques (SLR, VLBI, DORIS, PRARE)
  • other geodetic permanent observations (gravimetry)
  • time and frequency reference stations
  • tide gauges
  • sites of meteorological networks.

Although modern receivers can run unattendedly and remotey controlled, stations regularly manned with staff are nevertheless preferable.

Because geodetic links over several kilometers can be done by GPS with millimeter accuracy, it is not absolutely necessary that the permanent station is put to an existing geodetic marker. Other criteria like the colocation with other techniques or the connection to host computers are more important.

2.1 Instrument

The GPS receivers should

  • track both codes and phases on both frequencies under non-AS as well as AS conditions
  • track at least 8 satellites
  • track at least with 30 seconds sampling rate. If the sampling rate is faster, the data should be decimated to 30 seconds prior to upload to the Regional Data Centre
  • synchronize the actual instant of observation with true GPS time within (1 millisecond to the full second safety measures against mains power failures are highly recommended. If the data is downloaded in realtime to an external PC without being stored in the receiver for a certain time, the same safety measures have to include the PC, too
2.2 Antenna
  • The antenna should be protected against heavy snow load if necessary.
  • The manufacturer-proposed orientation of the antenna should be guaranteed.
  • The antenna should be used with the ground plane if available.
  • Elevation- (azimuth-) dependent phase centre variations should be known if necessary.
2.3 Marker

The marker should fulfill standard requirements for a first order geodetic monument with respect to stability, durability, long-term maintenance, documentation, and access.

Obstruction should be minimal above 15 degrees elevation.

Signal reception quality has to be verified, especially with respect to interference of external signal sources like radars, and with respect to multipath.

The antenna height corresponds to the vertical distance of the agreed-upon physical reference point (see antenna diagrams) on the antenna above the marker.

Local ties to other markers on the sites have to be determined in a coordinate system parallel enough to ITRS to guarantee the millimeter in all three directions. They are given in delta-x, delta-y, delta-z, x,y,z being the geocentric cartesian coordinates (ITRS).

2.4 Documentation

A standard IGS site description file should be filled out and sent to the EUREF Network Coordinator :


Blank forms are available through anonymous ftp at IGS Central Bureau Information System (CBIS) :

        File: igscb/station/log/BLNKFORM.LOG


IGN Institut Geographique Nationale (CBIS mirror site) :

        File: /pub/igscb/station/log/BLNKFORM.LOG

Additional site descriptions (photos, maps, etc) should be sent to the Network Coordinator.

3. Operational Centres

3.1 Responsibilities

The Operational Centres are the institutions controlling the sites of a particular (local) network from the operational point of view.

They are the link between the sites and the Data Centre that makes available the data to the Analysis Centres, other Data Centres or individual users.

The Operational Centres are responsible for

  • the downloading of the raw data from the receivers of the local network
  • the archiving of the raw data
  • the reformating of the data into the agreed-upon exchange format
  • quality check of the data on a station by station basis
  • the generation of status messages (abnormal conditions)
  • the alert/engagement of onsite personnel (abnormal conditions)
  • the upload of the data to the Data Centre at agreed-upon times

Within the International GPS Service for Geodynamics there are many independent tracking sites (e.g. Zimmerwald, Herstmonceux) that are not part of a local / special network and as such not connected to an actual Operational Centre. In this case the organization operating the site of course also performs the tasks outlined above.

3.2 Data Download From the Stations

The downloading from the receiver to the Operational Centre's computer system can either be done directly or indirectly through a small on-site computer, e.g. a PC :

     ----------        ------------
    | receiver |------| on-site PC |-----
     ----------        ------------      |      -------------------- 
                                         |-----| Operational Centre |
     ----------                          |      --------------------
    | receiver |-------------------------

The PC could even download the data from the receiver continually, using e.g. some manufacturer-provided download software.

The communication between the Operational Centre and the stations is done through dialup modem, Internet, special-purpose data links, Inmarsat, etc.

3.3 Data Archive

As the exchange data format does not conserve all information found in the raw data it should not be used for the primary data archiving. The Operational Centre is responsible for the long-term data archiving unless this task has been delegated to the sites. Usually the original raw data files or compressed (e.g. zipped) raw data files are archived.

The EUREF Regional Data Centre does archive the RINEX files for the general benefit of EUREF only.

3.4 Data Format

The data has to be prepared in daily (24 hours) RINEX files, both for observations and broadcast navigation messages.

The daily observation files contain the observations collected between 00:00:00 and 23:59:30 GPS time. The sampling rate (observation interval) has to be 30 seconds. In case of a higher original observation rate a decimation of the data to the currently adopted 30 seconds is mandatory.

The header information, especially the station name, receiver and antenna information, antenna height has to be up-to-date and has to strictly follow the agreed-upon conventions (see blank log forms for the stations).

The navigation message file contains all messages with TOC/TOE (time of clock, time of ephemeris) between 00:00 and 23:59 GPS time of the respective day.

It is recommended to generate a combined daily RINEX navigation file containing non-redundantly all navigation messages collected by all sites of the local network. The filename (part "ssss", see below) should then contain a 4-character code of the Operational Centre.
The RINEX files are prepared in a compressed form using the standard UNIX compress program. Compress and decompress programs for other platforms (PC/DOS, VAX and Alpha VMS) are available at the IGS CBIS (directory /igscb/software/compress).

The files are to be named according to the following table:

|  File Type        ASCII File                Compressed File                 | 
|                                     Unix           VMS           DOS        |
|Observation File  ssssdddf.yyO  ssssdddf.yyO.Z  ssssdddf.yyO_Z  ssssdddf.yyY |
|Navigation File   ssssdddf.yyN  ssssdddf.yyN.Z  ssssdddf.yyN_Z  ssssdddf.yyX |

ssss: 4-character station code	      
ddd : day of the year of the first record
yy  : year
f   : file sequence number within the day
      (0: containing all data of the day)

Files sent to another host have to be named on the target system in accordance with the target operating system:


      Put a file from a Unix to a VMS system:  binary
                                               put zimm1230.94O.Z zimm1230.94o_z
3.5 Data Validation

Data should be checked before sent to a Data Centre. A minimum verification should consist of a check of

  • the total number of observations
  • the total number of observed satellites
  • the date of the first observation record in the file
  • the station name, receiver/antenna types, antenna height

The use of a true quality check program is highly recommended, e.g. UNAVCO's QC program (available through the IGS Central Bureau Information System or at its mirror site at IGN, directory /igscb/software/qc).

3.6 Data Handling

It is highly recommended that all steps in the data handling (download from the receiver, reformatting, data validations, generation of statistics, data archving and transmissions be fully automated. Data failing to pass the validation step should be kept back for manual treatment.

3.7 Data Upload

The data has to be sent daily to the Regional Data Centre (Institute for Applied Geodesy, Frankfurt), via a Local Data Centre if appropriate, by anonymous ftp using binary (image) "put" :

           System: Unix
           Directory: /indata

For initial contacts and additional information write to :

           Heinz Habrich, IfAG :
3.8 Timeliness of the Data Transfer

Currently (March 1995) there is one EUREF Analysis Centre only (CODE in Berne) that routinely processes the data of the European Permanent Stations. As this data analysis is performed more or less simultaneously with the global IGS analysis the data has to be available within 48 hours after observation at the Analysis Centre, or 72 hours for Friday data.

As soon as other Analysis Centres are operating, this schedule might be changed.

Early 1995 CODE will change its procedure to allow for later arrival of the data. It is planned to process data that arrives at CODE within 7 days after observation.

Data that is not guaranteed to be processed should not be accumulated at the Regional Data Centre.

(Depending on the future number of stations and Analysis Centres it might well be that the processing of some stations is limited to certain time periods (e.g. two weeks every two months)).

3.9 Documentation

The IGS Central Bureau Information System makes available a blank form for an Operational Centre description file (blankform.ocn in /igscb/center/oper). This form should be filled out by the Operational Centre or by the agency operating an independent permanent GPS station and sent to the Network Coordinator.

4. Local Data Centres

4.1 General

Depending on the policy of the respective agencies the tracking data and the auxiliary station information of the local network can be openly made available through computer networks or bulletin boards etc. This task would be the responsibility of a Local Data Centre.

4.2 Data Access

It is recommended to allow access to (all or part of) the data through Internet's anonymous ftp, currently being the most effective and easy to use access method, especially for automated data download. Another access procedure on Internet is through World Wide Web (WWW) servers with easy to use browsers such as Mosaic or Lynx.

4.3 Available Information

It is recommended to make available at least the following information :

  • Station information (site log files)
  • Data Centre information (blank forms and examples can be found in the IGS CBIS (/igscb/center/dcn).
  • Other network information: Data flow, Operational Centre description, reference and access to other networks (EUREF, IGS, ...), ...
  • Daily tracking data (RINEX files), including results of quality checks
  • Data holding information (i.e. a machine-readable summary of the available tracking data). Examples can be found in the IGS CBIS (/igscb/data/holding). A program to generate such a data holding file can be obtained through the IGS Central Bureau.
  • Status information about the network and GPS in general and cross-references to other information systems
       	****** B B G H H J K K K L M M M M M N O O P T U V W W Z
         IFAG  O R R E F O I I O A A A A D E Y H N O R P I E T I
        ****** R U A R L Z R T S M D S T V T A I S T O A L T Z M
               1 S Z S K E U 3 G A R 1 E O S L G A S M D L T R M
	******* Last Update :  8-MAR-95 20:20 (Day 067) ********
	95-066 . 1 1 1 1 1 1 1 1 1 1 1 . . 1 1 1 1 1 1 . 1 1 . 1
	95-065 2 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 . 1 1 1 1
	95-064 2 1 1 1 1 2 1 1 1 2 1 1 1 2 1 1 1 1 1 1 2 1 1 1 1
	95-063 3 1 1 2 1 1 2 1 1 1 1 2 1 2 1 1 1 1 1 1 3 2 1 1 2
	95-062 1 1 1 1 1 1 3 1 1 1 1 3 1 2 1 3 1 1 1 1 4 3 1 1 1
	95-061 . 1 1 1 1 1 1 1 2 1 6 1 1 3 1 1 1 1 1 1 1 1 1 1 1
	95-060 2 1 1 1 1 1 1 1 . 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1
	95-059 2 1 1 1 1 2 1 1 . 2 2 1 1 2 1 1 2 1 1 1 . 1 1 1 1
	95-058 2 1 1 2 1 1 1 1 . 1 8 1 1 . 1 1 1 1 1 1 1 1 1 1 1
	95-057 2 1 1 1 1 1 1 1 1 1 3 1 1 . 1 1 1 1 1 1 1 1 1 1 1
	95-056 3 1 1 1 1 1 1 2 1 2 4 1 1 . 1 1 1 1 1 1 1 1 1 1 1

            Example of a data holding file for IfAG.
4.4 Data Organization

It is recommended to organize at least the tracking data in a hierarchical directory structure. From the user's point of view it is usually preferable to combine all the data of one day (or one week) into one directory than to have station-dependent directories. Examples of directory organizations can be found in the IGS Data Centre description files (CBIS, directory /igscb/station/dcn).
All the other information of course can be made available either through ASCII files in a directory tree or through more advanced means like data bases or hypertext documents or, preferably, through both.

The Local Data Centre description file and the daily updated data holding file should be made available to the IGS Central Bureau Information System.

4.5 Data Transfer to the Regional Data Centre

The tracking data of stations that are also part of an upperlevel network (EUREF, IGS) have to be forwarded through Internet to the Regional Data Centre (Institute for Applied Geodesy, Frankfurt), by anonymous ftp using binary (image) "put" :

            System: Unix
            Directory: /indata

For initial contacts and additional information write to :

           Heinz Habrich, IfAG :

5. Analysis Centres

All 7 IGS Analysis Centers process routinely at least some of the European permanent tracking stations. The Centre for Orbit Determination in Europe (CODE) currently processes all European sites made available to the European Regional Data Centre. With the growing number of permanent stations that could be used for the benefit of the European Reference System it might be necessary to distribute the processing to several Analysis Centres.

Such distributed processing is also in discussion in the IGS. The procedures of how to combine partial solutions (including an exchange format for solution exchanges) are currently developed.

The EUREF Analysis Centre(s) should generate a (combined) time series of coordinates of all permanent sites included in the EUREF Network with a resolution of 3 months or better.

The solutions are primarily based on the reference frames used within IGS, namely ITRF-yy, yy being some yearly realization. The transformation of the solutions to the European Reference System have to be performed according to the EUREF guidelines issued and updated by IGN.

6. Network Coordinator

The Network Coordinater coordinates and supervises all activities within the EUREF permanent network.

He/she is in permanent and close contact with

  • the local networks, either the through the Operational Centres or the Local Data Centres
  • the Regional Data Centre
  • the EUREF Analysis Centres
  • the EUREF Information Centre
  • the IGS Central Bureau

He/she proposes to the EUREF TWG the topology of the EUREF permanent network, i.e. the stations to be included/excluded, their data flow and coordinates their data analysis.

He/she monitors the data flow through the EUREF network.

He/she coordinates the flow of information within the EUREF network and towards the International GPS Service (IGS) and other organizations.

He/she prepares, in collaboration with all participating agencies, a yearly report.

       Dr. Carine BRUYNINX	        Tel.	+32 2 373 0292
       Observatoire Royal de Belgique	Fax:	+32 2 374 9822
       Avenue Circulaire 3		E-Mail:
       B - 1180 Brussels

has been appointed as EUREF Network Coordinator.

7. Information Exchange

The distribution of information within the network (i.e. between Operational, Data, and Analysis Centres) is preferably assured through e-mail. Stations operated by an independent Operational Centre do not have to be directly on the distribution lists. The information from and to these stations will flow through their Operational Centre.

The e-mail addresses should point to mailboxes that are checked at least once per working day. Fax and phone communication should be available, too.

It is recommended to subscribe to the IGSMail service run by the IGS Central Bureau (send e-mail to

8. Check List For Becoming a Permanent EUREF Station

  1. Contact the EUREF Network Coordinator concerning the intent to install the station, the schedule for implementation, and a statement of desire for the station to be considered as part of the permanent EUREF network.
  2. Follow the EUREF and IGS standards in installing the station.
  3. Once the station is installed and operational, a communication should be addressed to the EUREF Network Coordinator indicating data availability. Describe the planned data flow (including schedules) in details. Send a copy of the mail to the Regional Data Centre and to the EUREF Analysis Centre(s).
  4. The EUREF Network Coordinator will assist in the designation of the 4-character station identifier to prevent duplication
  5. The new station or its responsible Operational Centre has to create an IGS station log (blank formats are available at the IGS Central Bureau Information System and at its mirror site at IGN) :
    IGN mirror site :
        File: /pub/igscb/station/log/BLNKFORM.LOG
    IGS Central Bureau Information System (CBIS) :
        File: igscb/station/log/BLNKFORM.LOG
  6. Send the EUREF log file to the Institut Geographique Nationale (IGN) :
    and ask for the assignment of a DOMES number, and, if not yet known, a EUREF number. If appropriate, update the IGS log file with the DOMES number and send it to the EUREF Network Coordinator :
  7. Whenever modifications of the log files are necessary, first download the currently valid file from the Information System and send the updated file back through e-mail
  8. A sample file of each RINEX file type should be sent to the EUREF Regional Data Centre for verification.