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

GULFNET GPS Network - HAMM-Hammond P.S.
Start: 12-Feb-2001
End: 02-Jun-2019
Dokka, Roy K., 2001, GULFNET GPS Network - HAMM-Hammond P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T53B5X6Z