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

MAGNET - HRTM-HRTM P.S.
Start: 25-Feb-2015
End: 16-Jun-2021
Blewitt, Geoff, Hammond, William C., Kreemer, Corne, 2015, MAGNET - HRTM-HRTM P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T56971ZD