The products hosted at the IGETS data centers are:
- Level-1: Raw gravity and local air pressure records sampled at 1 or 2 seconds, in addition to the same records decimated at 1-minute samples;
- Level-2: Gravity and local air pressure data corrected for instrumental perturbations, ready for tidal analysis,
- Level-3: Gravity residuals after particular geophysical corrections, including solid Earth tides, polar motion, tidal and non-tidal loading effects.
Level-2 data products are obtained from the Level-1 raw gravity and pressure data, with a correction of the major instrumental perturbations using classical remove/restore techniques.
Level-3 gravity residuals are computed from the Level-2 data, after subtracting major geophysical contributions:
- Solid Earth tides and ocean tidal loading,
- Atmospheric loading,
- Polar motion and length-of-day induced gravity changes,
- Instrumental drift.
Tidal gravity variations are computed differently for the long-period tides and for the diurnal and sub-diurnal bands: at high frequency, a local tidal model, adjusted by least-squares, is used. At low frequencies the tidal signal is modeled based on the tidal potential and gravimetric factors from theory for the solid Earth tides, adding ocean tidal loading based on FES2014b.
Atmospheric loading is computed using MERRA2 hourly surface pressure, and assuming an inverted barometer ocean response to pressure.
The polar motion and length-of-day induced gravity variations are modeled using the pole coordinates the IERS, and assuming a gravimetric factor of 1.16, with an ocean pole tide as a self-consistent equilibrium response.
Depending on the sensor, the instrumental drift is generally modeled as a polynomial or an exponential function. When available, we use time series from absolute gravimeters for the adjustment.