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

GPS Soil Moisture Network - OKL1-Tower Monument Site A P.S.
Start: 01-Jun-2010
End: 02-May-2016
Larson, Kristine, 2010, GPS Soil Moisture Network - OKL1-Tower Monument Site A P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5QZ281H