The gravity field model ITSG-Grace2018
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When using the data please cite:

Mayer-Gürr, Torsten; Behzadpur, Saniya; Ellmer, Matthias; Kvas, Andreas;
Klinger, Beate; Strasser, Sebastian; Zehentner, Norbert (2018):
ITSG-Grace2018 - Monthly, Daily and Static Gravity Field Solutions from
GRACE. GFZ Data Services. http://doi.org/10.5880/ICGEM.2018.003

Unconstrained monthly solutions
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For each month of the observation period sets of spherical harmonic coefficients for different
maximum degrees (60, 96, 120) were estimated without applying any regularization. Daily variations
are co-estimated and eliminated from the normal equations. For most applications a spectral resolution
of degree 60 is sufficient. In some cases a higher resolution is preferable but in some rare months
the orbit configuration doesn't allow to solve for high degrees (e.g. 2004-09).

Processing Details
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The ITSG-Grace2018 gravity field solutions are computed using variational equations with an arc length of 24 hours.
In addition to satellite state and instrument calibration parameters, daily gravity field variations up to degree
and order 40 were modeled in the adjustment process.

K-band range rates with a sampling of 5 seconds and kinematic orbits with a sampling of 5 minutes were used as observations.
The kinematic orbits of the GRACE satellites (Zehentner and Mayer-Gürr 2013, 2014) were processed using the GPS orbits
and clock solutions provided by CODE. Additionally, a full accelerometer scale factor matrix was estimated per day
(Klinger and Mayer-Gürr, 2016). The accelerometer bias was modelled through cubic splines with a node interval of
six hours and estimated for each axis and day.

The following background models were used during the data processing:
    Earth rotation: IERS 2010
    Moon, sun and planets ephem.: JPL DE421
    Earth tide: IERS 2010
    Ocean tide: FES2014b, co-estimated
    Pole tide: IERS 2010
    Ocean pole tide: Desai 2004 (IERS 2010)
    Atmospheric tides: AOD1B RL06
    Atmosphere and Ocean Dealiasing: AOD1B RL06
    Sub-monthly continental hydrology: LSDM
    Relativistic corrections: IERS 2010
    Permanent tidal deformation: included (zero tide)

The above models were reduced during the analysis process. They are not present in the solutions.
The models are provided as mean value over the specific time spans (daily, monthly)
in the background directory.