GOCE Gravity Field Model

Space-Wise Solution - First generation

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Model Characteristics
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GOCE Input Data:
- The full list of input data to the space-wise model is provided in the IHD file.
- Basically the solution makes use of both satellite tracking data derived from the 
  on-board GPS receiver and gravity gradients observed by the on-board electrostatic 
  gradiometer.
- In particular kinematic orbits with their error estimates are used for SST gravity field 
  recovery, while reduced dynamic orbits are used for geo-locating gravity gradients. The 
  information coming from the electrostatic gradiometer are gravity gradients, common mode 
  accelerations and satellite attitude quaternions.
- Data period: 20091030T005757_20100111T073815

A-priori Information used:
- The main prior information used in the space-wise solution is the first GOCE quick-look 
  model (EGM_QLK_2__20091101T000000_20091230T000000_1001), while EGM2008 is used for degree 
  variance modelling and for error calibration of the estimated gravitational potential 
  along track. The latter use affects the low degrees of the solution.

Processing procedures:
- The space-wise approach is a multi-step collocation procedure, developed in the framework 
  of the GOCE HPF data processing for the estimation of the spherical harmonic coefficients 
  of the Earth gravitational field and their error covariance matrix.
- A SST model is derived by first estimating the gravitational potential along track by 
  applying the energy conservation approach to kinematic orbits.
- Then a spherical grid of potential values is computed at mean satellite altitude by 
  collocation and the spherical harmonic coefficients are derived by numerical integration 
  from the grid values.
- The SST+SGG model is computed by applying an iterative scheme which basically consists of 
  a Wiener orbital filter to reduce the strongly time correlated noise of the gradiometer, 
  a spherical interpolation at mean satellite altitude by jointly applying a local 
  collocation to the filtered potential (T) and gravity gradients (Txx, Tyy, Tzz, Txz) and, 
  finally, a harmonic analysis procedure by integration for the computation of the 
  geo-potential coefficients. The whole procedure is iterated to recover the signal 
  frequencies cancelled out by the Wiener orbital filter and to improve the rotation from 
  gradiometer to local orbital reference frames.
- The full error covariance matrix of the estimated spherical harmonic coefficients is 
  derived by Monte Carlo simulations.

References:
- GOCE data analysis: the space-wise approach and the first space-wise gravity field model.
F. Migliaccio (1), M. Reguzzoni (1), F. Sanso (1), C.C. Tscherning (2), M. Veicherts (2).
(1) DIIAR, Politecnico di Milano, Italy.
(2) Niels Bohr Institute, University of Copenhagen, Denmark.
Proceedings of the ESA Living Planet Symposium, 28 June - 2 July 2010, Bergen, Norway. 
See also: earth.esa.int/GOCE