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IERS Message No. 47                                       November 07, 2003
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Summary of the IERS workshop on site co-location surveys


A workshop devoted to „site co-location survey objectives, methods and
issues“ has been organized by the International Earth rotation and
Reference Systems Service (IERS). It took place in Matera / Italy on
October 23 / 24, 2003.

Presently the quality of the station coordinates results from the various
space techniques is in the order of a few millimetres in the horizontal and
about 1 cm in the vertical component. Precise local ties are the perfect
link to enable a rigorously combination of all space observing techniques
by their common parameters in order

  - to study the systematics going along with each space technique and,
  - to establish a unique, high-precision terrestrial reference frame.

In previous analysis one of the major limiting factors is the
characteristic and the availability of accurate local tie information for
all the co-located sites around the globe. In 5 sessions attention has been
given to:

  - Co-location sites and their importance for the ITRF
  - Site surveys
  - Analysis and SINEX
  - Reporting and Archiving
  - Planning for 2004

More than 30 participants from Australia, South Africa, USA and Europe
discussed various examples, analysis methods and survey strategies. Finally
guidelines for co-location site surveys and report templates have been
proposed. The potential availability of survey teams as well as the
planning for surveys in 2004 have been investigated.

The important recommendations are the following:

  - Local ties between co-located instruments should be determined with an
    accuracy of 1 mm, with full variance/covariance information, available
    in SINEX format.
  - Local survey measurements should have the same importance as and should
    be treated like any of the space geodetic techniques.Site coordinates
    (VLBI, GPS, SLR, DORIS) should be better tied to the ground. The local
    ties quality should be such that they can be assumed true for the
    combination.
  - All GPS sites close to other geodetic techniques should be part of the
    IGS routine processing.
  - A database will be established at IERS (Central Bureau and ITRS Product
    Centre) for all information in connection with site co-location (list
    of co-location sites, local ties in SINEX, co-location instruments,
    site maps and pictures, survey reports, survey status, site events and
    history …).

To support the local tie activities an IERS Working Group on Local Survey
will be suggested for adoption by the IERS Directing Board. The charter of
the working group will be the coordination and assistance in local tie
analysis as well as SINEX file generation.

The workshop information (programme, presentations and recommendations) is
available at the IERS web-page

            http://www.iers.org/workshop_2003_matera/

The proceedings will be published as IERS Technical Note No. 33.

With best regards
Bernd Richter
IERS Central Bureau, Director


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