Analysis of Global Positioning System (GPS) data demonstrates that ongoing three-dimensional crustal deformation in Fennoscandia is dominated by glacial isostatic adjustment. Our comparison of these GPS observations with numerical predictions yields an Earth model that satisfies independent geologic constraints and bounds both the average viscosity in the upper mantle (5 x 10(20) to 1 x 10(21) pascal seconds) and the elastic thickness of the lithosphere (90 to 170 kilometers). We combined GPS-derived radial motions with Fennoscandian tide gauge records to estimate a regional sea surface rise of 2.1 +/- 0.3 mm/year. Furthermore, ongoing horizontal tectonic motions greater than approximately 1 mm/year are ruled out on the basis of the GPS-derived three-dimensional crustal velocity field.

Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube-and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of 39 nm/s 2 and long-term stability of 0.5 nm/s 2 , short-term noise of 96 nm/s 2 / √ Hz. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related fields, such as continuous absolute gravity monitoring with a single instrument under rough environmental conditions. arXiv:1512.05660v1 [physics.atom-ph]

[1] Data collected under the auspices of the BIFROST GPS project yield a geographically dense suite of estimates of present-day, three-dimensional (3-D) crustal deformation rates in Fennoscandia [Johansson et al., 2002]. A preliminary forward analysis of these estimates has indicated that models of ongoing glacial isostatic adjustment (GIA) in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3-D velocity field. In this study we revisit our previous GIA analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the BIFROST rate estimates. To establish insight into the physics of the GIA response in the region, we begin by decomposing a forward prediction into the three contributions associated with the ice, ocean, and rotational forcings. From this analysis we demonstrate that recent advances in postglacial sea level theory, in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin, involve peak signals that are larger than the observational uncertainties in the BIFROST network. The forward analysis is completed by presenting predictions for a pair of Fennoscandian ice histories and an extensive suite of viscoelastic Earth models. The former indicates that the BIFROST data set provides a powerful discriminant of such histories. The latter yields bounds on the (assumed constant) upper and lower mantle viscosity (n UM , n LM ); specifically, we derive a 95% confidence interval of 5 Â 10 20 n UM 10 21 Pa s and 5 Â 10 21 n LM 5 Â 10 22 Pa s, with some preference for (elastic) lithospheric thickness in excess of 100 km. The main goal of the (Bayesian) inverse analysis is to estimate the radial resolving power of the BIFROST GPS data as a function of depth in the mantle. Assuming a reasonably accurate ice history, we demonstrate that this resolving power varies from $200 km near the base of the upper mantle to $700 km in the top portion of the lower mantle. We conclude that the BIFROST data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer. However, these data provide little constraint on viscosity in the bottom half of the mantle. Finally, elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity.INDEX TERMS: 1208 Geodesy and Gravity: Crustal movements-intraplate (8110); 1236 Geodesy and Gravity: Rheology of the lithosphere and mantle (8160); 8107 Tectonophysics: Continental neotectonics;

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The gravity anomalies at sea level can be used to validate the satellite gravity gradiometry data. Validation of such a data is important prior to downward continuation because of amplification of the data errors through this process. In this paper the second-order radial derivative of the extended Stokes' formula is employed and the emphasis is on least-squares modification of this formula to generate the second-order radial gradient at satellite level. Two methods in this respect are proposed: a) modifying the second-order radial derivative of extended Stokes' formula directly, b) modifying extended Stokes' formula prior to taking the second-order radial derivative. Numerical studies show that the former method works well but the latter is very sensitive to the proper choice of the cap size of integration and degree of modification.

S U M M A R Y An observation model for earth tide displacements in application to Very Long Baseline Interferometry and similar precise geodetic techniques is developed. It incorporates effects from anelasticity, ellipsoidal figure, and fluid core resonance. Based on a harmonic development of the external potential, the model follows the familiar Love number concept. The transfer function of the earth to each harmonic is formulated in terms of coupled harmonics in the space domain and fulfils the causality condition in the time domain. Solve-for parameters can be chosen flexibly. The guideline, however, has been to provide a minimum set of well-defined and well-resolvable tide response parameters for analysis of observations. The aim of accuracy for tide displacements prediction is below 1 mm.Being the major perturbation of the solid earth tide, ocean tide loading effects are computed, and the accuracy of the models involved is discussed. It appears that the major error source relates to those ocean tide frequencies for which global models are not available. These frequencies form a continuum with a power spectrum being largely a result of non-linear tide interaction. The associated loading effects cannot be reliably interpolated from global tide models, which are available only for a few distinct frequencies and which disregard tidal intermodulation. Thus, an accuracy of 1 mm for computed loading tide displacements cannot always be achieved.

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We present sea level observations derived from the analysis of Signal-to-Noise Ratio (SNR) data recorded at five coastal GPS sites. These sites are located in different regions around the world, both in the northern and the southern hemisphere, in different multipath environments, from rural coastal areas to busy harbors, and experience different tidal ranges. The recorded SNR data show periodic variations that originate from multipath, i.e. the interference of direct and reflected signals. The general assumption is that for satellite arcs facing the open sea, the SNR variations are due to reflections off the sea surface. The SNR data recorded from these azimuth intervals were analyzed by spectral analysis with two approaches, a simple analysis approach assuming static sea level during a satellite arc, and an extended analysis approach that involves a time dependent sea level during a satellite arc. The GPS-derived sea level results were compared to sea level records from co-located traditional tide gauges, both in the time and frequency domain. The sea level time series are highly correlated with correlation coefficients on the order of 0.89 − 0.99. The root-mean-square (RMS) differences are on the order of 6.2 cm for stations with low tidal range (up to 165 cm) and 43 cm for stations with high tidal range (up to 772 cm). The relative accuracy, defined as the ratio of RMS and tidal range, is between 2.4 % and 10.2 % for all stations. The results based on the extended SNR-analysis approach agree better with the tide gauge results, than the results of the simple approach, for the stations with high tidal range. For the station with the highest tidal range (772 cm), the RMS is reduced by 47 % when using the extended approach. Furthermore, the results also indicate that the simple approach assuming a static sea level can be used for stations with a tidal range of up to about 270 cm, without performing significantly worse than the extended analysis approach. Tidal amplitudes and phases were derived by harmonic analyses of the sea level records. Again, a high level of agreement is observed between the tide gauge and GPS-results. The results based on the extended SNR-analysis approach show a higher degree of agreement with the tide gauge results, than the results of the simple approach for stations with large tidal range. Spectral analysis of the residuals after the harmonic analysis reveals remaining signal power at multiples of the draconitic day. This indicates that the observed SNR data are to some level disturbed by additional multipath signals, in particular for GPS sites that are located in harbors.