In this investigation a consistent combination of the complementary data types of satellite observations and the available terrestrial gravity field measurements in Austria is considered. For this purpose, the well known Remove-Compute-Restore technique is adapted to perform long-and short-wavelength signal reductions. The long-wavelength effect is represented by a global satellite-only model in terms of spherical harmonics. The shortwavelength are modeled by topographic masses in the spatial domain. As the topographic reduction contains also long-wavelength effects a possible double consideration has to be avoided. Alternatively to Least Squares Collocation (LSC) method (Moritz 1980a) a least squares approach with parametrization as Radial Basis Functions (RBF) is applied. The RBF approach has the advantage that an increasing number of observations can be included in the calculations and a downsampling of the available data, as it is required in LSC, will no longer be necessary. Another advantage is that RBF is to able to handle an inhomogeneous input data distribution. The very first outcomes are verified by comparing with independent GPS/leveling observations. instance, with the GOCE mission it is possible to derive a global gravity field model parametrized in terms of a spherical harmonic series expansion up to a degree and order (D/O) of 250 corresponding to a spatial resolution of approximately 80 km half wavelength. The accuracy in terms of geoid height with 100 km spatial resolution is 1-2 cm (Drinkwater et al. 2008). However, for regional applications the spatial resolution of a satellite-only gravity field model is insufficient. Many local and regional applications require a much higher spatial resolution than a satellite-only model can provide. On the other hand, local gravity field models derived from terrestrial and airborne gravity field data e.g. gravity anomalies or deflections of the vertical reflect the small scale features better as the satellite data but lack from long-wavelength information. Therefore a pure gravimetric geoid solution is affected by long-wavelength errors (Pail et al. 2009).
<p>The Swarm satellite constellation provides GPS data with sufficient accuracy to observe the large-scale mass transport processes occurring at the Earth&#8217;s surface since 2013. We illustrate the signal content of the time series of monthly gravity field models. The models are published on quarterly basis and are the result of a combination of the individual models produced by different gravity field estimation approaches, by the Astronomical Institute of the University of Bern, the Astronomical Institute of the Czech Academy of Sciences, the Institute of Geodesy of the Graz University of Technology and the School of Earth Sciences of the Ohio State University. We combine the models at the solution level, using weights derived from a Variance Component Estimation, under the framework of the International&#160;Combination&#160;Service for&#160;Time-variable&#160;Gravity Fields (COST-G).</p><p>&#160;</p><p>We estimate the monthly quality of the models by comparing with GRACE and GRACE-FO products and illustrate the improvement of the combined model as compared to the individual models. We present the high signal-to-noise ratio of this uninterrupted time series of models, smoothed to 750km radius, over large hydrological basins. Finally, we compare the behavior of degree 2 and 3 coefficients with GRACE/GRACE-FO and SLR.</p>
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