International Terrestrial Reference System

The ITRS is the agreed international, Earth-fixed, global terrestrial reference system of Cartesian coordinates that form the ITRF.

The abbreviation stands ITRS system for IERS Terrestrial Reference or (simplified) for International Terrestrial Reference System, ITRF for IERS Terrestrial Reference Frame.

It is the result of an ongoing collaboration between institutions from geodesy, space and astronomy, and an important part of Earth Rotation Service International Earth Rotation and Reference Systems Service (IERS ).

  • 2.1 External links

Definition of the reference system

Its origin is the geocenter ( the center of mass of the Earth), the position of the earth's surface resulting from the orbits of artificial satellites. The Z axis is the central axis of rotation of the earth ( the reference pole IERS ), the x-axis falls within the 0 ° meridian plane (Greenwich ), which is defined by coordinates of reference stations (see below ITRF ). The Y-axis completes the tripod of the legal system.

Since the origin and the axes of a coordinate system in nature are generally not materially realized and can be made available, the definition of which is provided by a more or less large number of fixed or fixed points. The system is then realized indirectly by the coordinates of these fixed points, and from the Reference System is a Reference Frame ( " the Framework" ) from concrete numerical values. For example, the (dormant ) inertial system of astronomy (International Celestial Reference System ICRS ) is realized by a few hundred quasars and their link with the star coordinate system of the FK5. The "System Earth" rotates within this inertial system and in turn - like a big, precise gyro - defined by its gyro axis and its rotation. So on the Earth's body - - For this, however, " points to the roundabout " itself must be defined:

Realization by measurements and ITRF

This particular shape of the ITRS is called ITRF (F -frame, " coordinate frame "). ITRF currently consists of about 400 globally distributed, high-precision measurement points ( partially at observatories and fundamental stations ), determine numerically their positions and plate tectonic movements, the ITRS. The ITRF - points are accurate and integrated land surveying in the respective (regional).

The determination of the coordinates and their longer-term changes

  • By methods of satellite geodesy - especially with GPS, supplemented (from ~ 2010, Galileo) by GLONASS
  • And the Doppler radio system DORIS
  • And laser measurements ( laser ranging ) to the moon and earth satellites (LLR, SLR)
  • And their link to the astrometric system of the most accurate star catalog FK5.

Viewed from another angle, one could also say:

  • The coordinate frame ITRF is the list of coordinates, while
  • The reference system ITRS the geometry and dynamics of the earth describes. It contains the theory and the associated constants.

Years solutions of ITRF

The earth is not a rigid body, but are external and internal forces of up to a certain degree after. Already by the tides caused by the moon "breathes " the earth by about half a meter. Influences of plate tectonics cause permanent displacements of continents by 1-10 cm per year, while the accuracy of the geoscientific measurements increases continuously.

Therefore, it is necessary to improve the system of reference by continuous measurement and refine the models. Since the 1990s, the most accurate measurement methods are partially to " years solutions " combined - an international collaboration of IUGG institutions and the IERS Earth Rotation. The largest regular contributions from Europe to IERS / ITRF / ICRF represent the VLBI and GPS measurements of BKG dar.

The rotation data of these years solutions have now ( compared to the system of quasars ) precision achieved <1 cm, over a number of years even 3 mm or 0.0001 ". , The continental drift is taken into account by specific mathematical conditions (eg no net translation / rotation). these model solutions will receive a year; particularly accurate through various projects solution was ITRF97, which served to compare different models present the ITRF2000 ( and in the future probably 2005) is used for such purposes. .

ITRF 2005

Compared to the ITRF2000 results in several improvements and new features. Firstly, it contains data until the end of 2005, so that newer stations could be considered, or old stations were significantly improved coordinates. Also for the first time non-linear movements station are taken into account by, for example, by earthquake, a new coordinate were estimated for these stations.

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