Dear all,

Somewhat belatedly, here we present the results of the consultation with the Services and the community on the definition of GGOS Core Sites, together with our conclusions and decisions on this topic [1].

We thank everyone who took their time to ponder the issue and provided feedback, those who facilitated and promoted the conversation with their colleagues, and of course the governing bodies of the four IAG Services we approached requesting their opinion.

As you recall, we wanted to gather your views on the question of how to define GGOS Core Sites, in preparation for the work on the update of the requirements for observatories. You can find in [1] all the explanations, a summary of the feedback received, and what we concluded. In short, we did not find consensus on a possible update of the definition, and therefore the decision is not to change anything at this point, but to clarify any issues in the soon-to-be-updated documentation.

Additionally, a number of points were raised by many respondents and the Services, such as the paramount importance of the local tie surveys, and some sort of quality criteria that observatories ought to fulfil. For this reason, other than providing clarity where it may be needed, we are recommending some additional requirements, the details of which are to be worked out by the team of experts who will contribute to the updated GGOS Requirements for Core Sites [2].

For this, a few of you have already expressed your willingness to participate in this work in your area of expertise. We would like now to formally request volunteers for the task of revisiting the GGOS Requirements for Core Sites document [2], so that we can start working on it after summer. We will be looking at an update that takes into account the conclusions from the consultation, advances in the relevant technologies and best operational practices.

While the consultation and the conclusions presented in [1] refer only to the geometric reference frame, we have already contacted colleagues from the gravity and physical heights areas, who have provided relevant documentation which, always following their lead on these topics, will be incorporated to the existing material.

Please let us know if you would be happy to collaborate on this; all the help we can get will be much appreciated and the final result will be as good as your contributions. Beyond the circumscribed issue of the mandatory requirements, there is ample room here for recommendations and best practices, which only you can provide. Please distribute this email and the linked document as you deem appropriate.

Best regards,

José Rodríguez & Martin Lidberg

GGOS Bureau of Networks and Observations

[1] https://doi.org/10.5281/zenodo.21532614

[2] https://geodesy.science/wp-content/uploads/GGOS-CoreSites-Requirements_v2_2015.pdf