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

MAGNET - SHEP-SHEP P.S.
Start: 28-Jun-2011
End: 27-Jul-2017
Blewitt, Geoff, Hammond, William C., Kreemer, Corne, 2011, MAGNET - SHEP-SHEP P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5ZS2TP3