Dear Colleagues,

This email is addressed to the owners, operators and surveyors of ITRF Co-location sites.



I hope that you are all safe and healthy in this unprecedented and terrible pandemic situation.



In building and operating Core co-location sites, your contribution is fundamental to


global geodesy and to the ITRF in particular.



The four IAG services (IDS, IGS, ILRS and IVS) are currently reprocessing their data

in preparation for their contribution to the ITRF2020. The ITRF2020 Call for Participation


is available here: http://itrf.ign.fr/doc_ITRF/CFP-ITRF2020.pdf



Recent and past results of local surveys at ITRF co-location sites are solicited for inclusion

in ITRF2020 analysis. Local ties should be provided in SINEX format, with full variance covariance

information, together with a report if available.

If more than one local surveys were operated, at different epochs, we kindly ask you to make all

the results available: one SINEX per local survey results.

In the scope of the activity of the IAG working group WG 1.2.1 Methodology for surveying geodetic

instrument reference points (joint with IERS), co-location site survey and survey product metadata

are being collected. When submitting your local tie SINEX file(s), we kindly ask you to fill in and


send the excel sheet/form available at the following link:



http://itrf.ign.fr/local_surveys.php



Please submit your files to:

ITRS Center: itrf@ign.fr

and

IERS Central Bureau: central_bureau@iers.org



The IERS ITRS Product Center is particularly grateful to all the institutions that provide the necessary investment for the space geodetic observatories which constitute the main ITRF foundation.

Counting on your valuable contributions.

Sincerely Yours

Zuheir Altamimi

Head, ITRS Center

President, International Association of Geodesy