Network description
IERS Station list
The initial definition of the IERS network
The IERS network was initially defined through all tracking instruments used by the various individual analysis centers contributing to IERS. Therefore, all SLR, LLR and VLBI systems were included. Then, GPS stations from IGS were added as well as DORIS tracking network.
The network also included, since its inception, a selection of ground markers, specifically those used in case of mobile equipments and those currently included in local surveys performed for monitoring local eccentricities between instruments in case of collocation sites or for site stability checks.
Each point is currently identified by the attribution of a DOMES number. The explanation of the DOMES numbering system is given below.
Neighboring points are clustered into a site. The current rule is that all points which could be linked by a collocation survey (up to 30 km) should be included into a single site of the IERS network having a single DOMES site number.
Co-locations
In the frame of IERS, the concept of co-location can be defined as the fact that two instruments simultaneously or sequentially occupy very close locations which are very precisely surveyed in three dimensions. In more details, several cases can be of interest:
- simultaneous or non simultaneous measurements
- instruments referring to the same technique or not
As typical illustrations of the potential use of such data, we can mention:
- calibration of mobile systems, for instance SLR or GPS antennas, using simultaneous measurements of instruments referring to the same technique
- repeated measurements on a marker with mobile systems (for instance mobile SLR or VLBI), using non simultaneous measurements of instruments referring to the same technique
- changes in antenna location for GPS or DORIS
- co-locations between instruments referring to different techniques, which implies eccentricities, except in the case of successive occupancies of a given marker by various mobile systems
Usually, co-located points should belong to a single IERS site.
Extensions of the IERS network
Recently, due to the requirements of various user communities, the initial IERS network has been expanded to include new types of systems which are of potential interest. Consequently, the present types of points allowed in IERS and for which a DOMES number can be assigned are (IERS uses a one letter code for each type):
- satellite laser ranging (SLR) (L)
- lunar laser ranging (LLR) (M)
- VLBI (R)
- GPS (P)
- DORIS (D) also Doppler NNSS in the past
- optical astrometry (A) - formerly used by BIH -
- PRARE (X)
- tide gauge (T)
- meteorological sensor (W)
For instance, the cataloguing of tide gauges co-located with IERS instruments, in particular GPS or DORIS is used for the GLOSS program under the auspices of UNESCO.
Another advantage is to collect accurate meteorological surface measurements, in particular atmospheric pressure, in order to derive raw tropospheric parameters, such as the integrated profiles of precipitable water vapor, from tropospheric propagation delays that can be estimated during the processing of radio measurements, e.g. made by the GPS, VLBI, or DORIS space techniques.
Other systems could also be selected if they were considered helpful (for instance systems for time transfer, super-conducting or absolute gravimeters...)
These improvements were developed to support the conclusions of the CSTG Working Group on Fundamental Reference and Calibration Network.
Another important extension is the hope of some continental or national organizations to see their fiducial networks included in the IERS network, either to be computed by IERS (for instance the EUREF permanent GPS network) or at least to get a DOMES number (for instance the CORS network in USA). Such extensions are supported by the IAG Commission X on Global and Regional Geodetic Networks (GRGN) in order to encourage the use of ITRS.