Co-location usings Clocks and New Sensors

Chair: Ulli Schreiber (Germany)


Terms of Reference

The establishment of accurate local ties of different space geodetic techniques at fundamental geodetic observatories poses a long-standing problem. While geometric ties can be determined at sub-millimeter-level, the relation to physical phase centers of the instruments and temporal stability of such offsets are usually known with significantly lower precision. Novel ways for inter-technique calibration at a geodetic site need to be developed using existing and new sensors and technologies, such as highly accurate time and frequency transfer, ultra-stable clocks, and co-location targets. Complementary to such development the tying of techniques shall be exploited to their limits at the analysis level e.g. to using common clock and troposphere parameters.


The main objective of the working group is the investigation of new methods and technologies to cross-calibrate space geodetic sensors at geodetic observatories and to exploit common parameters at the analysis level. The working group will

  • Investigate new technologies for inter-technique calibration of sensors at geodetic observatories;
  • Investigate the capabilities of accurate time and frequency distribution between sensors at geodetic observatories and between observatories;
  • Investigate the long-standing discrepancy in scale coming from VLBI and SLR;
  • Address the use of new sensors such as ring lasers, quantum sensors, etc.;
  • Further assess the contribution of estimation of common parameters at analysis level to the stability and accuracy of geometric local ties and the consistency of combined global reference frames.

To this purpose it closely interacts with the IERS WG on Site Survey and Co-location and the Joint WG 1.1.6 on Tropospheric Ties.