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

Greenland GNSS Network - HEL2-Helheim Glacier P.S.
Start: 01-Jan-2019
End: 14-Nov-2022
SDFE, The Danish Agency, 2007, Greenland GNSS Network - HEL2-Helheim Glacier P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/S98C-T637

Greenland GNSS Network - HEL2-Helheim Glacier P.S.
Start: 24-Aug-2007
End: 14-Nov-2022
SDFE, The Danish Agency, UNAVCO Community, Bevis, Michael, 2007, Greenland GNSS Network - HEL2-Helheim Glacier P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/7PB0-2Z53

Greenland GNSS Network - HEL2-Helheim Glacier P.S.
Start: 01-Jan-2012
End: 31-Dec-2018
UNAVCO Community, 2007, Greenland GNSS Network - HEL2-Helheim Glacier P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/5FGP-SP27

Greenland GNSS Network - HEL2-Helheim Glacier P.S.
Start: 24-Aug-2007
End: 31-Dec-2011
Bevis, Michael, 2007, Greenland GNSS Network - HEL2-Helheim Glacier P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5SJ1HNK