GOCE Gravity Field Model

Time-Wise Solution - First generation

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Model Characteristics
----------------------
GOCE Input Data:
- Gradients: EGG_NOM_2
- Orbits: SST_PKI (kinematic orbits); SST_PCV (variance information of kinematic orbit 
  positions)
- Attitude: EGG_IAQ_2C
- Data period: 20091101T000000:20100111T000000

A-priori Information used:
- No a-priori gravity field information applied (neither as reference model, nor
for constraining the solution)

Processing Procedures:
- Gravity from orbits (SST):
- energy integral applied to kinematic orbits, degree/order 100
- orbit variance information included as stochastic model
- Gravity from gradients (SGG):
- parameterization up to degree/order 224
- realistic stochastic modelling by applying cascaded digital filters to the observation
equations

Combined solution:
- addition of normal equations (SST D/O 100, SGG D/O 224)
- Constraints: Kaula-regularization applied to (near-)zonal coefficients,
  and to coefficients of degrees/orders 170 - 224 (contraints towards zero)
- Optimum weighting based on variance component estimation

Specific Features of resulting Gravity Field:
- Gravity field solution is independent of any other gravity field information
- Constraint towards zero starting from degree/order 170 to improve signal-to-noise ratio
- Related variance-covariance information represents very well the true errors of the 
  coefficients
- Solution can be used for independent comparison and combination on normal equation level 
  with other satellite-only models (e.g. GRACE), terrestrial gravity data, and altimetry
- Since in the low degrees the solution is based solely on 2 months of kinematic GOCE 
  orbits, but no external (GRACE) information, it is not competitive with a GRACE model in 
  this frequency range.

References:
- GOCE gravity field model derived from orbit and gradiometry data applying the time-wise
method; Roland Pail (1), Helmut Goiginger (2), Reinhard Mayrhofer (2), Wolf-Dieter
Schuh (3), Jan Martin Brockmann (3), Ina Krasbutter (3), Eduard Hoeck (4), Thomas
Fecher (1);
(1) TU Muenchen, Institute of Astronomical and Physical Geodesy, Arcisstrasse 21,
80333 Muenchen, Germany
(2) Graz University of Technology, Institute of Navigation and Satellite Geodesy,
Steyrergasse 30, 8010 Graz, Austria
(3) University of Bonn, Institute of Geodesy and Geoinformation, Nussallee 17,
53115 Bonn, Germany
(4) Austrian Academy of Sciences, Space Research Institute, Schmiedlstrasse 6,
8042 Graz, Austria
Proceedings of the ESA Living Planet Symposium, 28 June - 2 July 2010, Bergen, Norway, 
See also: earth.esa.int/GOCE
- Wolf-Dieter Schuh (1), Jan Martin Brockmann (1), Boris Kargoll (1), Ina Krasbutter (1), 
Roland Pail (2); Refinement of the stochastic model of GOCE scientific data and its effect 
on the in-situ gravity field solution
(1) Institut of Geodesy and Geoinformation, Department of Theoretical Geodesy, University 
of Bonn, 53115 Bonn, Germany
(2) Institute for Astronomical and Physical Geodesy, TU Muenchen, 80333 Munich, Germany
Proceedings of the ESA Living Planet Symposium, 28 June - 2 July 2010, Bergen, Norway; 
See also: earth.esa.int/GOCE