US Government security requirements no longer permit CDDIS to offer data via traditional unencrypted anonumous ftp; this service was discontinued on October 31, 2020. All data are still available, however access must be via HTTPS or ftp-ssl.

Instructions with examples and our FAQ can be found at: https://cddis.nasa.gov/Data_and_Derived_Products/CDDIS_Archive_Access.html.

If you still have difficulty after reading and attempting the examples on that page, please contact us at support-cddis@earthdata.nasa.gov.

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Space Geodesy Techniques

Geodesy is the science of the Earth’s shape, gravity and rotation, including their evolution in time. A number of different techniques are used to observe the geodetic properties of the Earth including the space-geodetic techniques of Global Navigation Satellite Systems (GNSS), like the US Global Positioning System (GPS), Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and the French Doppler Orbitography and Radio-Positioning by Integrated Satellite (DORIS) system. These space-geodetic observations also provide the basis for the reference frame that is needed in order to assign coordinates to points and objects and thereby determine how those points and objects move over time.

The Crustal Dynamics Data Information System (CDDIS) was initially developed to provide a central data bank for NASA's Crustal Dynamics Project (CDP). The system continues to support the space geodesy and geodynamics community through NASA's Space Geodesy Program as well as NASA's Earth Observing System Data and Information System (EOSDIS). The CDDIS was established in 1982 as a dedicated data bank to archive and distribute space geodesy related data sets. Today, the CDDIS archives and distributes GNSS (primarily Global Positioning System GPS and GLObal NAvigation Satellite System GLONASS), laser ranging (both to artificial satellites, SLR, and lunar, LLR), VLBI, and DORIS data for an ever increasing user community of geophysists.

The CDDIS is operational on a dedicated computer system located at the Goddard Space Flight Center in Greenbelt, MD.

The CDDIS has served as a global data center for the International GPS Service (IGS) since 1992. The CDDIS supports the International Laser Ranging Service (ILRS), the International VLBI Service for Geodesy and Astrometry (IVS), the DORIS Pilot Experiment, a precursor to the International DORIS Service (IDS), and the International Earth Rotation Service (IERS) as a global data center.

To learn more about these space geodetic techniques and their respective CDDIS data holdings, click on the menu items at left or on the images below.

GSNSS
SLR
VLBI
DORIS