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

Popocatepetl GPS Network - POSW-Popo Southwest P.S.
Start: 25-Apr-1996
End: 02-Jul-2003
Cabral-Cano, Enrique, 1996, Popocatepetl GPS Network - POSW-Popo Southwest P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T5ST7N2N