The following information obtained from UNAVCO's online DOI system:
(https://www.unavco.org/data/doi/search/search.html)

MAGNET - GRAV-GRAV P.S.
Start: 10-Aug-2006
End: 29-Mar-2022
Blewitt, Geoff, Hammond, William C., Kreemer, Corne, 2009, MAGNET - GRAV-GRAV P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5BZ647N