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

GPS Soil Moisture Network - RAYN-Rayon P.S.
Start: 30-Mar-2015
End: 27-Jun-2016
Larson, Kristine, 2016, GPS Soil Moisture Network - RAYN-Rayon P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5ZG6QMC