Access to IGS Data

W. Gurtner
Astronomical Institute, University of Berne
gurtner@aiub.unibe.ch

Summary

These guidelines summarize the data organization of the IGS and describe the procedures on how to access the data of the IGS tracking sites.

1. IGS Data Organization

The main components of the International GNSS Service, formerly the International GPS Service, are:

  • Tracking stations
  • Operational Centers
  • Data Centers
  • Analysis Centers and Associate Analysis Centers
  • Central Bureau with the Central Bureau Information System

1.1 Tracking Stations

The IGS is based not only on components set up and operated for the use and benefit of IGS but takes as much as possible profit from existing stations and centers. Many contributing tracking sites are part of some local network (e.g CORS of the U.S. National Geodetic Survey, the Australian permanent network of AUSLIG). Data of such sites are usually collected by the Operational Center (i.e. the organization responsible for running the network), reformated into the RINEX format and made available to the (local) user through a Local Data Center. Only the data of those sites being declared as IGS sites are then sent to an IGS Data Center.

In some areas a network of permanent sites covering a whole region has been organized that consists of a selection of local network stations plus a number of individual stations. The data of the individual stations are sent directly to the Regional Data Center, those of the other sites through their Local Data Center. An example of a regional network is EUREF covering the whole of the European continent. (EUREF also has its own Analysis Centers, Information System, and Network Coordinator).

The IGS network finally consists of individual tracking stations sending their data directly to an IGS Global Data Center and a selection of the regionally or locally organized sites that send their data to the IGS through the Regional or Local Data Centers.

For the purposes of rapid, global products, the IGS consequently distinguishes between Global, Regional, and Local Sites. Global sites are those sites that are analysed by more than two IGS Analysis Centers, at least one of which as to be on a different continent. The data of such sites of global interest have to be available at the Global Data Centers.

IGS keeps track of all sites of global and regional interest.

Site logs:

The Central Bureau Information System (CBIS) maintains site logs for each one of the acknowledged IGS tracking sites. Site logs contain the full history of the station, e.g. the dates of all changes of receivers or antennas. The Information System also contains a summary file of the currently valid most important parameters of the stations and a similar summary file with the full history of those parameters.

A global map of the IGS tracking sites can be found at the Central Bureau Information System.

1.2 Operational Centers

Operational Centers are those institutions reponsible for the operation of a (local) network of tracking stations, usually doing the reformating of the raw data, ensuring administrative and technical support of the sites, etc.

Individual stations perform these duties themselves.

1.3 Data Centers

Data Centers make available the tracking data of the respective stations to the users, usually by anonymous or username/password protected ftp access.

IGS distinguishes between Global, Regional, and Local Data Centers.

Within IGS there are three Global Data Centers that each collect and redistribute (at least) the data of the global sites and a number of Regional Data Centers acting under the guidelines of IGS.

Global Data Centers

  • CDDIS: Crustal Dynamics Data Information System at NASA, Greenbelt MD, USA
  • SIO : Scripps Institution of Oceanography, UCSD, La Jolla CA, USA
  • IGN : Institut Geographique National, Paris, France

Regional (and Special Networks) Data Centers

  • BKG : Bundesamt fuer Kartographie und Geodaesie, Frankfurt, Germany: European Data Center
  • GA: Geosciences Australia, formerly AUSLIG
  • NRCAN (formerly EMR): Natural Resources of Canada
  • NGS: NOAA-National Geodetic Survey (US)
  • JPL: Jet Propulsion Laboratory: NASA's Global Network

IGS keeps track of all Global and Regional Data Centers. It may also make available information of Local Data Centers.

  • The IGS Central Bureau Information System contains all the informations about the data centers, such as contact addresses, data and disk organization, access information (if public).
  • The IGS Data Centers daily generate/update standardized files of the actual data holdings, where the user can find which observation files have been received (and when) by the center (see below).
  • The CBIS generates monthly and yearly summary files showing the data of which stations have been collected by the IGS Data Centers during the respective time period (see below).

1.4 Analysis and Associate Analysis Centers

The IGS Analysis Centers perform routine analysis of at least the global sites and generate the requested products such as precise orbits, Earth rotation parameters, station coordinates and velocities, etc. The individual solutions of the products are combined into official IGS products and made available to the users through the IGS Analysis Centers and the Information System.

Associate Analysis Centers perform specific analysis, regional densification or combinations of products.

1.5 The Central Bureau Information System (CBIS)

The IGS Central Bureau maintains an information system (CBIS) containing all information a user of the services provided by IGS needs to know. It consists of a Web site as well as an ftp server. The ftp server is mirrored by the Global Data Center in Europe at IGN.

It also makes available some of the IGS products, such as precise orbits and Earth rotation parameters.

2. Data Format and Data Flow

The tracking data is made available in daily RINEX files. All tracking sites generate at least a daily RINEX observation and navigation message file. Some of the stations additionally generate a RINEX meteorological data file provided they are equipped with high-precision weather sensors and/or a summary file with quality check information.

2.1 Observation Files

Naming conventions:

Unix VMS
   
ssssdddf.yyD.Z ssssdddf.yyD_Z
   
ssss: 4-character station code  
ddd : day of the year  
f : file sequence number (0 for 24-hour file)  
yy : two-digit year  

.Z and _Z: Files are compressed using the UNIX Z compression scheme. For DOS and VMS systems decompression software is available at the CBIS.

The D in the filename extension denotes observation files that are additionally compressed using the Hatanaka obs file compression scheme.

There might still be observation files available that have not yet been compressed with the Hatanaka scheme. Their filename extension is .yyO.Z and .yyO_Z respectively.

The four-character station code is at least within the IGS network a unique identifier of the currently used IGS antenna marker at a tracking site. A worldwide and over the time unique identifier is the so-called DOMES number to be found in the station log and the MARKER NUMBER field of the RINEX file headers.

File contents:

Currently the standard data rate is 30 seconds. Data files contain observations for a 24 hour period, from 00:00:00 till 23:59:30 GPS time. Every effort is taken to show actually valid information in the RINEX file headers. However, it is strongly recommended to consult the station log files, as these files are supposed to contain the official site information.

2.2 Navigation Message Files

The navigation message files contain the broadcast messages collected by the respective tracking stations between 00:00 and 23:59 GPS time.

Naming conventions:

Unix VMS
   
ssssdddf.yyN.Z ssssdddf.yyN_Z
   
ssss: 4-character station code  
ddd : day of the year  
f : file sequence number (0 for 24-hour file)  
yy : two-digit year  

.Z and _Z: Files are compressed using the UNIX Z compression scheme.

Global Navigation Message File:

The Global Data Center CDDIS daily generates a file containing one copy of all broadcast messages collected by all IGS sites:

Unix VMS
   
BRDCdddf.yyN.Z BRDCdddf.yyN_Z

It can be accessed at CDDIS and IGN in the usual navigation message file directories.

2.3 Meteorological Files

Some of those stations equipped with high-precision weather sensors daily submit RINEX met files, too. It is recommended that all IGS stations implement and operate precision met equipment wherever possible.

Naming conventions:

Unix VMS
   
BRDCdddf.yyM.Z BRDCdddf.yyM_Z

2.4 Summary Files

Some of the stations run their daily data through a quality check program the output of which is reported in the files

Naming conventions:

Unix VMS
   
BRDCdddf.yyS.Z BRDCdddf.yyS_Z

2.5 Data Flow

Depending on the status of a tracking stations the daily RINEX files are sent by binary ftp from the stations/Operational Centers (via Local Data Centers) to the nearest Regional or one of the Global Data Centers. A diagram of the actual data flow can be found in the CBIS.

The data of those stations used for daily orbit and ERP computation is usually available within half a day at all three Global Data Centers.

Data of regional interest only can be found at the respective Regional Data Centers.

3. How to Access IGS Tracking Data

3.1 Identification of the Tracking Sites

  • Check the global map or the global site list for the location of the IGS tracking sites. Note the 4-character station abbreviations of the suitable sites.

    Note:

    In some areas there are permanent GPS networks with sites not necessarily kept track of by IGS and hence not included into the IGS maps, lists and directories.

    Examples:

  • Download the currently valid site log files from CBIS.

    Filename convention:

    ssssmmyy.log
     
    ssss: 4-character station code
    mm : month of log file creation/update
    yy : year

3.2 Identification of the Data Center

3.3 Data Download

  • Contact the Data Center by phone, fax or e-mail to get confidential access information if necessary
  • Connect to the center by ftp or http, go to the data directories according to the DC's data organization, download the data files by binary ftp.
  • Decompress the files using the utilities provided by IGS.

Before using the data verify the contents of the RINEX headers with the station log files or the summary history file.

3.4 Receiver/antenna information

For the generation of IGS products, the IGS Analysis Centers use a standard file containing phase center information for the GPS antennas used on the tracking sites. This file igs_01.pcv can also be accessed at the CBIS.

3.5 ITRF Coordinates of the Tracking Sites

The Subbureau for Reference Frames of the International Earth Rotation Service (IERS/ITRF) periodically generates new global solutions of station positions and velocities based on VLBI, SLR, and GPS (IGS) data analysis. These solutions, called ITRF-yy (International Terrestrial Reference Frame, yy = year of the solution), are available at the IERS Subbureau. The unique identifier and cross reference for the markers is the DOMES number.

Please forward questions to IGSCB


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This page last updated: 19 Dec 2006
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