Local Geometric and Gravimetric Datum and its Relation to the Global Terrestrial Reference System

Abstract

In active tectonic zones relative earth surface displacements of mm-order and relative gravity disturbances of 0.1 mgal size may be expected between two survey epochs. To monitor and separate these small effects significantly special local free networks have to be designed which are measured by relative observations of highest accuracy (mm-and μgal-level). For the connection of the local nets to a global terrestrial reference system a suitable local datum for point coordinates (geometric datum) and gravity field parameters (gravimetric datum) has to be defined within the terrestrial reference system.

The definition of the local datum is given and its dependency on the relative observation type discussed. For the datum realisation mainly satellite techniques are proposed. The tolerance interval of the datum parameters with respect to the global terrestrial system are analysed. Adjustment results referred to the local datum can directly be transformed into the terrestrial system without loss of significance, if the datum does not exceed the tolerance intervals. As a consequence requirements for the fundamental stations establishing the terrestrial reference system are discussed.