Crustal Dynamics Data Information System (CDDIS) of the National Aeronautics and Space Administration (NASA), Receiver Independent Exchange Format (RINEX) files CDDIS http://cddis.gsfc.nasa.gov

National Geophysical Data Center (NGDC) of the National Oceanic and Atmospheric Administration, Ionosonde Standard Archiving Output (SAO) files NGDC ftp://ftp.ngdc.noaa.gov/

Technical University Munich, German Geodetic Research Institute, An Open Altimeter Database TUM http://openadb.dgfi.tum.de

University Cooperation for Atmospheric Research (UCAR), COSMIC Data Analysis and Archive Center UCAR http://www.cosmic.ucar.edu/data.html