Please complete the protocol for Session 2 "Realization of the ITGRF".

Date

15.09.2026

Presentation by Ezequiel Antokoletz and Andreas Engfeldt    

• Reference station classifications
  • Rather the prescribe reference station requirements – perhaps start with what kind of stations we already have
  • ITGRF proposes 3 types of stations, but perhaps more are needed
• Reference Station
  • Provide a long term, stable gravity refereence function (RF)
  • SG + AG
  • Continuous AG
  • ~6 AG observations per years
• Comparison Stations
  • Multiple AGs
• Core stations
  • GGOS , GNSS, SLR, VLBI

• Need to monitor medium and long term changes in gravity. (RF) 
• Argentina example of 30uGal change over 5+ years. (Hungary yesterday, similar).   Lucky to have both FG5 and SG
• Matera Italy an example of only AG time series

• Current Station Status

• Core and comparison: 6
• Core and reference: 3
• Comparison: 12
• Reference: 9

• Comparison Status
  • CIPM and Regional Key Comparisons. CIPM every 7-8 years, RMO between
  • Additional “geodetic” comparisons? How often?
  • Need to document equivalence of all AGs

General Discussion

• Comparison site meant to measure at different places at different times
• Reference stations handle same place at different times
• A “monitor” station where you come and compare with local RF
• Mirjam/Alex: reference function is necessary when you don’t have an AG to compare with.   If you have AGs you can compare anytime/anywhere
• Vojtech: reference station simply monitors gravity – accuracy may vary widely between RSs.   (Let’s figure out comparison stations later).   This is enough to access the Frame
• Each RS may have its own “uncertainty” class
• Using local RSs as a control/check when doing a survey in another country/area is another purpose.
• Derek: list of all participating stations with attributes that users can “select” from if they need a local check/confirmation of equivalence
• Sylvain: important to distinguish Comparison stations
• Vicki: ITRF has contributors whose inputs are monitor by a coordination/analysis center.   This is how quality/uncertainty is established.
• Alex: reference function can serve as a tie to the frame (metrology)
• Vojtech: Comparisons can happen anywhere – don’t even need to be at RSs. 
• Derek: perhaps the ability to host comparisons is simply another attribute of an RS.
• Przemek: we do want as many RSs as possible!
• Ezequiel: not every nation needs an RS

Resolved to Resolve on Wednesday:   Frame is defined by  RSs and comparisons at RSs.    Define stations by collection of attributes and capabilities.