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

GPS Soil Moisture Network - MFLE-Marshall Field East P.S.
Start: 17-Dec-2011
End: 14-May-2020
Braun, John, 2011, GPS Soil Moisture Network - MFLE-Marshall Field East P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5GT5K9D