Variance component estimation for co-estimated noise parameters in GRACE Follow-On gravity field recovery

Temporal gravity field modelling from GRACE Follow-On deals with several noise sources polluting the observations and the system of equations, be it actual measurement noise or mis-modellings in the underlying background models. One way to collect such deficiencies is to co-estimate additional pseudo-stochastic parameters in the least-squares adjustment which are meant to absorb any kind of noise while retaining the signal in the gravity field and orbit parameters. In the Celestial Mechanics Approach (CMA) such pseudo-stochastic parameters are typically piece-wise constant accelerations set up in regular intervals of e.g., 15 min, and an empirically determined constraint is added to confine the impact of the additional quantities. As the stochastic behaviour of these parameters is unknown because they reflect an accumulation of a variety of noise sources, Variance Component Estimation (VCE) is a well established tool to assign a stochastic model to the pseudo-stochastic orbit parameters driven by the observations.
In the simplest case the magnitude of the constraints of the pseudo-stochastic orbit parameters can be determined fully automatically.

We present results for GRACE Follow-On gravity field recovery when extending the CMA by stochastic models for the piece-wise constant accelerations computed with VCE and provide noise and signal assessment applying the quality control tools routinely used in the frame of the Combination Service for Time-variable gravity fields (COST-G).