EarthExplorer Help Index is now located at: https://www.usgs.gov/centers/eros/science/earthexplorer-help-index
GloVis Help Index is now located at: https://www.usgs.gov/centers/eros/science/glovis-help-index
HDDS Explorer Help Index is now located at: https://www.usgs.gov/centers/eros/science/hdds-explorer-help-index
All Data Dictionaries have been moved to the USGS site, usgs.gov or https://www.usgs.gov/search?keywords=data+dictionary
If you have any further questions, please contact the helpdesk as custserv@usgs.gov