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

Afar GPS Network - DASM-Semera CGPS P.S.
Start: 10-Mar-2007
End: 28-Oct-2009
Calais, Eric, 2008, Afar GPS Network - DASM-Semera CGPS P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T53T9F9V