Data processing

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Antennas on the ground receive raw telemetry from satellites. These raw data must be processed by applying corrections and combining them with complementary data before they are usable. Data are processed to different levels:
Level 0: raw telemetry
Level 1: time-tagged data located and corrected for perturbing effects (level 1, 1.5 and 1b data fall into this category)
Level 2: geophysical data (GDR-M) time-tagged, precisely located and corrected for environment effects. Data at this level are used by specialists with a close knowledge of their subject.
Level 3: data ready for immediate use in applications, crrected and/or inter-calibrated.
Level 4: gridded or model output data.
Depending on the mission, retracking is performed at level 1 or 2.