GRACE-FO RL04 GNV1B frame and origin for 2025–2026 dates

[nijanthan]

Hello PO.DAAC and GRACE-FO team,

I am comparing GRACE-FO C orbit positions from JPL's Level-1B RL04 GNV1B products with TU Graz orbit products and would appreciate clarification on the coordinate conventions for these dates:

2025-02-17

2025-03-04

2025-03-18

2025-04-17

2026-06-04

The collection is GRACEFO_L1B_ASCII_GRAV_JPL_RL04, DOI 10.5067/GFL1B-ASJ04. Section 3.2.3 of the September 2019 Level-1 handbook identifies ITRF2014 at the time of writing and notes that the realization may change.

Could you please confirm:

Which terrestrial reference-frame realization was used for each of these dates, and whether any processing transitions or reprocessing affect that identification?

The terrestrial origin convention, including whether a geocentre translation is applied when producing GNV1B coordinates from the underlying GNSS/network solution.

Whether the reported satellite positions refer to the spacecraft centre of mass, and which applicable offset/calibration documentation defines that reference point.

Where we can find the corresponding dated processing notes or transformation documentation, including the Earth-orientation inputs needed if using the associated GNI1B product.

This relates to PO.DAAC support ticket #114696. We have retained the exact daily files and checksums and can provide them to the processing team if needed. A documentation link or referral to the GRACE-FO Level-1 orbit-processing team would be very helpful.

Thank you,
Nijanthan Vasudevan
West Virginia University