Please complete the protocol for Session 3 "Representation of the ITGRF with gravity networks".
Date
Presentation by Martin Lederer and Vojtech Palinkas
Replacing IGSN71: ~2000 stations
ITGRS: “Acceleration of frefall” (metrology) and Zero Tide, Standard atmosphere, Earth rotation axis, IERS reference pole (geodesy)
General rules/guidelines for Absolute stations of ITGRF and Connected stations to ITGRF
Scheme: Reference stations and traceable absolute stations (the frame, ITGRF) disseminate to ITGRF “Connected” stations (not part of frame. ITGRF.XY)
Traceable Absolute Stations (TAS):
Compatible with ITGRF definition
Geodetic traceability (link to comparison ) demonstrated
Uncertainty based on repeated measurements. < 10 uGal? Includes (inflated by) e.g. environmental signals
Reference Stations
Same compatibility as TASs
+ Gravity variations have to be monitored
Connected Stations
Tie to AG points satisfying above-mentioned conditions
Physical monumentation
Data processing standards (adjustment, archiving, documentation)
Accuracy requirements <20uGal?
General Discussion
Ezequiel: no need to for numbering or epochs with new ITGRF. Just need traceable instrument participation. Question on how to include/initialize existing national networks?
Derek: look to GNSS perhaps as an example of how stations are included (or added or removed) over time and still have a well defined frame
Vojtech: if existing networks are established with AGs that have been shown to be in equivalence, then they are “automatically” consistent with the new ITGRF
Sylvain: we have not mentioned Field Stations yet. Vojtech: such stations fall under “Connected” . Sylvain: but they can also be part of the Frame as well
Mirjam: their network has traceable absolute observations, but because of uplift, requires an epoch
Alex: agreed, but stresses traceability
Derek: agrees with Sylvain: a standalone point in the middle of nowhere with a traceable instrument is an extension / addition to the frame.
Vojtech brings up IHRF definition and seems to include local/regional densifications in addition to core stations – all of which contribute/define IHRF.
Ezequiel: Field stations are Implementation / Densification of the ITGRF
Derek: imagine an application that requires a global fit of all surface gravity. They would not discriminate by the station category: they would simply perform a fit weighted by some station uncertainty
Andreas: DTU relies on field stations to anchor their airborne surveys. Ideally traceable and should be part of the frame.
Derek: role of the data coordinator is to assess and weight of each station’s data. Possible requirement for a “Reference Site” is routine, standard format delivered by the local coordinator (?)
Ezequiel: important to keep as much information as possible and keep the guidelines as simple as possible for the widest, easiest implementation via IUGG resolution.
Derek: agreeing with Hartmut that everything in Agrav is compatible with (or could be part of?) the ITGRF.
Hartmut: still undiscussed / undecided: how to include or not existing relative networks. Need guidelines. Possibly support such inclusion via new absolute measurements.
Martin: next session we need to establish formally the role of data coordinators.
Vojtech is worried about someone blindly measuring gravity of poor quality that will be part of the frame’s definition.