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

MAGNET - GARD-GARD P.S.
Start: 20-Mar-2007
End: 03-Jun-2018
Blewitt, Geoff, Hammond, William C., Kreemer, Corne, 2009, MAGNET - GARD-GARD P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5WW7FTN