On 31 October 2020, anonymous ftp access will officially be discontinued at CDDIS. CDDIS is STRONGLY recommending all users begin to transition to using alternate method of access to the CDDIS archive. Examples of alternate methods can be found at: https://cddis.nasa.gov/Data_and_Derived_Products/CDDIS_Archive_Access.html.

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CDDIS: NASA's Archive of Space Geodesy Data
About the CDDIS GNSS data and products archive

Global Navigation Satellite Systems (GNSSs), such as the U.S. GPS, the Russian GLONASS, and the European Galileo system, provide autonomous geo-spatial positioning with global coverage. Ground (or space-based) receivers collect the signals from orbiting satellites to determine their location in three dimensions and calculate precise time. These receivers detect, decode, and process both pseudorange (code) and phase transmitted by the GNSS satellites.

Since 1992, the CDDIS has supported GNSS data and product archiving for the International GNSS Service (IGS) as one of four global data centers. In this capacity, the CDDIS provides online access to the GNSS data generated by the IGS network as well as the IGS standard, working group, and pilot project products derived from these data.

GNSS receiver
GNSS receivers detect, decode, and process signals from the GNSS satellites (e.g., GPS, GLONASS, Galileo, BeiDou, and others). The satellites transmit the ranging codes on two radio-frequency carriers, allowing the locations of GNSS receivers to be determined with varying degrees of accuracy, depending on the receiver and post-processing of the data.